Exoplanet Status Report: Observation, Characterization and

ISSN 0038�0946, Solar System Research, 2010, Vol. 44, No. 4, pp. 290–310. © Pleiades Publishing, Inc., 2010.Original Russian Text © H. Lammer, A. Hanslmeier, J. Schneider, I.K. Stateva, M. Barthelemy, A. Belu, D. Bisikalo, M. Bonavita, V. Eybl, V. Coudé du Foresto, M. Fridlund, R.Dvorak, S. Eggl, J.�M. Grieβmeier, M. Güdel, E. Günther, W. Hausleitner, M. Holmström, E. Kallio, M.L. Khodachenko, A.A. Konovalenko, S. Krauss, L.V. Ksanfomality, Yu.N. Kulikov,K. Kyslyakova, M. Leitzinger, R. Liseau, E. Lohinger, P. Odert, E. Palle, A. Reiners, I. Ribas, H.O. Rucker, N. Sarda, J. Seckbach, V.I. Shematovich, A. Sozzetti, A. Tavrov, M. Xiang�Grüβ, 2010, published in Astronomicheskii Vestnik, 2010, Vol. 44, No. 4, pp. 314–335.

290

Exoplanet Status Report: Observation, Characterization and Evolution of Exoplanets and Their Host Stars1

H. Lammer1, A. Hanslmeier2, J. Schneider3, I. K. Stateva4, M. Barthelemy5, A. Belu6, D. Bisikalo7, M. Bonavita8, V. Eybl9, V. Coudé du Foresto10, M. Fridlund11, R. Dvorak9, S. Eggl9,

J.�M. Grieβmeier12, M. Güdel9,13, E. Günther14, W. Hausleitner1, M. Holmström15, E. Kallio16, M. L. Khodachenko1, A. A. Konovalenko17, S. Krauss1, L. V. Ksanfomality18, Yu. N. Kulikov19, K. Kyslyakova22, M. Leitzinger2, R. Liseau21, E. Lohinger9, P. Odert2, E. Palle13, A. Reiners22,

I. Ribas23, H. O. Rucker1, N. Sarda24, J. Seckbach25, V. I. Shematovich7, A. Sozzetti26, A. Tavrov16, M. Xiang�Grüβ27

1 Space Research Institute (IWF), Austrian Academy of Sciences, Graz, Austria2 Institute for Geophysics and Meteorology (IGAM), University of Graz, Austria

3 Observatoire Paris�Site de Meudon LUTH, Paris, France4 European Science Foundation, Standing Committee for Physical and Engineering Sciences, Strasbourg, France

5 Laboratoire de Planétologie de Grenoble CNRS�UJF, Grenoble, France6 Université de Bordeaux, France

7 Institut for Astronomy (INASAN), Russian Academy of Sciences, Moscow, Russia8 Osservatorio Astronomico di Padova, INAF, Italy

9 Institute for Astronomy, University of Vienna, Vienna, Austria10 Observatoiré de Paris—LESIA, Paris, France

12 ASTRON, Dwingeloo, The Netherlands13 ETH Zürich Astrophysics Institute of Astronomy, Zürich, Switzerland

14 Instituto de Astrofisica de Canarias, Tenerife, Spain15 The Swedish Institute of Space Physics, Kiruna, Sweden16 Finish Meteorological Institute (FMI), Helsinki, Finland

17 Institute of Radio Astronomy in Kharkov of the Ukrainian Academy of Sciences, Ukraine18 Space Research Institute (IKI), Russian Academy of Sciences, Moscow, Russia

19 Solar Geophysical Institute (PGI), Russian Academy of Sciences, Murmansk, Russia20 Institute for Applied Physics (IAP), Russian Academy of Sciences, Nizhny Novgorod, Russia

21 Onsala Space Observatory Chalmers University of Technology, Onsala, Sweden22 Universitát Göttingen, Institut für Astrophysik, Göttingen, Germany

23 Institut d’Estudis Espacials de Catalunya, Barcelona, Spain24 Astrium Ltd, Stevenage, United Kingdom

25 The Hebrew University of Jerusalem, Jerusalem, Israel26 INAF—Osservatorio Astronomico di Torino, Torino, Italy

27 Institut für Theoretische Physik und Astrophysik, Universitát zu Kiel, Kiel, GermanyReceived February 18, 2010

Abstract—After the discovery of more than 400 planets beyond our Solar System, the characterization ofexoplanets as well as their host stars can be considered as one of the fastest growing fields in space science duringthe past decade. The characterization of exoplanets can only be carried out in a well coordinated interdiscipli�nary way which connects planetary science, solar/stellar physics and astrophysics. We present a status report onthe characterization of exoplanets and their host stars by reviewing the relevant space� and ground�basedprojects. One finds that the previous strategy changed from space mission concepts which were designed tosearch, find and characterize Earth�like rocky exoplanets to: A statistical study of planetary objects in order toget information about their abundance, an identification of potential target and finally its analysis. Spectralanalysis of exoplanets is mandatory, particularly to identify bio�signatures on Earth�like planets. Direct charac�terization of exoplanets should be done by spectroscopy, both in the visible and in the infrared spectral range.The way leading to the direct detection and characterization of exoplanets is then paved by several questions,either concerning the pre�required science or the associated observational strategy.

DOI: 10.1134/S0038094610040039

SOLAR SYSTEM RESEARCH Vol. 44 No. 4 2010

EXOPLANET STATUS REPORT: OBSERVATION, CHARACTERIZATION 291

1 INTRODUCTION

The European Science Foundation (ESF) is anassociation of 80 member organizations devoted toscientific research in 30 European countries with theaim to advance and connect European research cen�tres and to explore new directions for research at thehighest scientific level. During the year 2009 the Inter�national Year of Astronomy was celebrated. One of themost important and interesting problems in modernastrophysics is the discovery of exoplanets. Becauseexoplanet research becomes more and more impor�tant an ESF sponsored Exploratory Workshop washeld in the village of Bairisch Kölldorf, Austria, 29thNovember–1st December 2009 (see Fig. 1). The char�acterisation of these discoveries has evolved dramati�cally since the first detection of the first Jupiter�typeobject more than a decade ago. Now more than 400exoplanets are known and the near future observingfacilities become extremely powerful. After the recentdiscoveries of transiting small and low mass exoplanetslike CoRoT�7b with 1.65REarth by the CNES�ledEuropean CoRoT�space observatory and the discov�ery by the ground based MEarth�project in the USA ofthe 2.68REarth size planet GJ1214b, one can expect that

1 The article is published in the original.

potentially habitable rocky exoplanets will be discov�ered during the not so distant future.

The workshop addressed three main aspects:—The first objective focused on the discussion of

the present status related to exoplanet research, exist�ing and future mission concepts, including space andground�based projects.

—The second objective was related to the charac�terisation of the host stars of potential terrestrialexoplanets. Because it is from fundamental impor�tance—related to habitability and atmosphere evolu�tion—to observe and analyze the activity, radiationand plasma environment and the ages of exoplanetaryhost stars various methods for obtaining observationalevidence of the radiation environment, Coronal MassEjections (CMEs) and stellar winds as well as the stel�lar age were addressed.

—The third objective was a survey of exoplanet orhost star characterisation relevant projects/researchcarried out at present, in non�EU Eastern Europeancountries especially the Russian Federation and theUkraine, so that exoplanet science activities becomemore known to researchers in these countries and newscientific cooperation’s can be established.

Besides these objectives discussions and plans toestablish a coordinated effort, which bring togetherdifferent research groups and project leaders so that

Fig. 1. The workshop participants in front of the ESF�workshop location in Hotel Legenstein, in Bairisch Kölldorf, Austria. Fromleft 3th row: Alessandro Sozzetti, Alexander Tavrov, Ignasi Ribas, Enric Palle, Rene Liseau, Nicola Sarda, Martin Leitzinger,Siegfried Eggl, Ansgar Reiners, Eike Günther, Dmitry Bisikalo, Rudolf Dvorak, Jean Schneider; From left 2th row: Leonid Ksan�fomality, Ivanka K. Stateva, Elke Lohinger, Jean�Mathias Grieömeier, Kristina Kyslyakova, Helmut Lammer, Adrian Belu, MatsHolmström, Valery I. Shematovich, Mathieu Barthelemy; From left 1th row: Mariangela Bonavita, Manuel Güdel, Joseph Seck�bach, Yuri N. Kulikov, Arnold Hanslmeier.

5

292


LAMMER et al.

ground�based and space�based observations ofexoplanets and their host stars can be coordinated inthe best way, were also carried out. This status reporton exoplanet projects and research summarizes themain points of the two day workshop.

SPACE MISSIONS DESIGNED FOR THE DETECTION

AND CHARACTERISATION OF HABITABLE EXOPLANETS

We are in an era where the field of exoplanetologyevolves very rapidly in three aspects: new scientificresults, new scientific ideas, new technological ideaand development. This makes the science�politicalsituation evolving permanently. It is therefore difficultto develop a definitive roadmap; here we describe thesituation as it is in early 2010. On the US side, theDecadal Survey Astro2010 is currently working on USplans. The outcome is foreseen for late 2010. On theEuropean side, in September 2004 the EuropeanSpace Agency ESA organized its Cosmic Vision2015–2025 workshop, at UNESCO in Paris, Francewhich brought together scientists from all over Europewhere they could present and outline what theythought should be the major issues of space explora�tion during 2015–2025, focusing on four majorthemes such as:

—What are the conditions for planet formationand the emergence of life?

—from gas and dust to stars and planets;—from exoplanets to biomarkers;—life and habitability in the Solar System;—How does the Solar system work?—What are the Fundamental Physical Laws of the

Universe?—How did the Universe originate and what is it

made of?This exercise showed that Europe is richer than

ever in ideas for what should be done in space sciencein the coming years. ESAs Cosmic Vision 2015–2025programme aims at furthering Europe’s achievementsin space science and is based on a massive response bythe scientific community to ESA’s call for themes,issued in April 2004.

Finally after advises and stepwise evaluations of theESA advisory bodies such as the Astronomy WorkingGroup (AGW) one M�class exoplanet mission,namely PLATO and the low cost mission of opportu�nity contribution to the Japanease SPICA telescopewere selected 2007 and will be further studied in com�petition with other M�class missions for a possiblelaunch date around 2017. One should also mentionthat the Dark Energy Cosmology mission Euclidwhich is also studied within the Cosmic Vision pro�gramme has a so�called Extra Euclid Survey ScienceProgramme (EESSP) where a microlensing surveycould be planned during the extensions of the Euclid

mission. A 3�month extension of the Euclid missionwould be sufficient to undertake a unique microlens�ing survey of the Galactic Bulge, reaching detectionlimits which would include planets similar to those inour solar system with masses larger than Mercury.

In 2008 ESA has initiated an expert advisory teamof advising the space agency on the best scientific andtechnological roadmap to address questions related tothe characterization of terrestrial exoplanets up to thepossible detection of biomarkers on Earth�like planetsand the preparation of an exoplanet roadmap in orderto fulfill the scientific goals of the Cosmic Vision2015–2025 scientific plan with respect to exoplanetsand especially terrestrial bodies orbiting stars otherthan our Sun.

Shortly after the Exoplanet Roadmap AdvisoryTeam (EPRAT) was formed, an open Call for WhitePapers for the European science community wasissued. During August 2008 and 2010 the EPRATteam evaluates the papers as well as suggestions byinterested scientists and takes them into account in thepreparation of a final report. An open workshop orga�nized by ESA as part of the EPRAT process will beheld in UCL, London, UK during April 7–8, 2010,were the exoplanet roadmap will be discussed betweenparticipating scientist and the EPRAT team. Feed�backs from the scientific community will be includedin the final report, which is intended to be finishedduring summer 2010 and the final roadmap will bepresented to ESA, the ESA advisory bodies and theworld wide scientific community in general.

Besides the exoplanet roadmap exercises of the bigspace agencies, the exoplanet science communityestablished the so�called Blue Dots team, which isorganized around a core of coordinating groups ofexperts in several themes which cover:

—exoplanet targets and their environments;—formation and evolution of planetary systems;—habitability criteria;—observations of exoplanetary atmospheres and

relevant detection techniques:—single aperture imaging;—multiple aperture imaging;—microlensing;—radial velocities;—astrometry;—transits;—exoplanet modeling, including habitability studies.Besides these scientific subjects a main concern is

related to public outreach and education, the stepwisebuilding of a well organized and structured Europeanexoplanet community, European networking andfunding search, acting as an interface with the industryand observers/contact points for international collab�oration. In first steps scientists involved to the BlueDots team are also connected to the EU FP7 fundedEuroplanet project within the Na2 working groupsExoplanets and other planetary systems (WG5) and



Magnetic worlds, the Sun�planet connection (WG4).The Blue Dot team works, like the ExoPTF in theUSA and the EPRAT in Europe on a report, which willalso be released during the first half of 2010 to the sciencecommunity, space agencies and decision makers.

However, one of the most important aspects will beinternational cooperation with space agencies besidesESA, NASA and JAXA (e.g. in Russia, China, India,etc.). Given the budgetary limitations in any coun�tries, cooperations in larger space missions will beessential. ESA, JAXA and NASA cannot in the com�ing decade build a large mission by their own.

EXISTING, PLANNED, AND FUTURESPACE PROJECTS RELEVANT

FOR THE CHARACTERISATION OF EXOPLANETS

At present (March 2010), there are two spaceobservatories, namely CoRoT (CNES�led European)and Kepler (NASA) in orbit, which search exoplanetswith the transit method. Transits of Earth�sizeexoplanets produce a small change in the host startsbrightness of about 1/104 lasting for 2–16 hours. Thischange must be absolutely periodic if it is caused by aplanet and if possible at least three times confirmed. Inaddition, all transits produced by the same planet mustbe of the same change in brightness and last the sameamount of time, thus providing a highly repeatable sig�nal and robust detection method. The size of theplanet is found from the depth of the transit and thesize of the star.

The CoRoT and Kepler Space Observatories

The CoRoT (Convection, Rotation and planetaryTransits) space observatory is led by the French spaceagency CNES, in a cooperation with ESA, Austria,Brazil, Belgium, Germany and Spain. Initially thegoal of the CoRoT mission was the observation andstudy of variable stars via asteroseismology. After the

discovery of the first hot Jupiter in the mid 90ies—thesearch for exoplanets was included in the mission pro�gram. CoRoT was successfully launched on December27 from the Baikonour Cosmodrome, and the firstobservations started during February 2007 (Fig. 2).Besides the discovery of several exosolar gas giants(e.g., Dvorak et al., 2010; see also special issue Astron.Astrophys., Vol. 506, 1, Oct. IV, 2009; Lammer et al.,2010; article on CoRoT discoveries in this issue),CoRoT detected the first transiting rocky super�Earth�type planet with a size of about 1.68 REarth(Léger et al., 2009). The life�time of the mission wasscheduled for 3 years of observations and recently theextension for another three years was approved.

The CoRoT satellite has a length of about 4 m, adiameter of about 2 m and weights about 630 kg. Theaccuracy of the pointing is 0.5 arcsec with a capacity ofthe telemetry of 1.5 Gbit/day. Three systems are oper�ating on the satellite. CoRoTel is an afocal telescopewith 2 parabolic mirrors and aperture of 0.27 m and acylindric baffle with a length of 2 m. CoRoTcam is awide field camera consisting of a dioptric objective of6 lenses where the focal unit is equipped with 4 frame�transfer�CCD 2048 × 4096. Two of the four CCDs arefor the exoplanet program and two are for the seismol�ogy program. Finally CoRoTcase is hosting the elec�tronics and the software managing the aperture pho�tometry processing. A total number of 12000 stars andmagnitudes between 11 and 16 are observed in theexoplanet mode. CoRoT polar orbit of the satelliteallows observing 150 days, the long run, and between20 and 30 days the short run, both in the direction ofthe center respectively anticenter of the galaxy.

Radial velocity measurements to confirm planetcandidates are usually performed with the 3.6 mHARPS spectrograph in La Silla, the 1.93 m SOPHIEspectrograph in the Observatoire de Haute Provence,the CORALIE spectrograph in La Silla, the Coud’eechelle spectrograph from the 2 m telescope in Tau�tenburg (TLS), Germany and the UVES and

Meilleurs Voeux pour 2007

Best Wishes for 2007

de la pert de toute l‘equipe CoRoTfrom all the CoRoT Team

Launch

December 27 th 2006

14:23 UT

The CoRoT Soyuz Rocket on the launchpad of the Baikonour Cosmodrome

Fig. 2. Left, the CoRoT space observatory at the top of a Soyuz rocket on the launch path of the Baikonour Cosmodrome, shortbefore the launch (insert) and right an illustration of the satellite in orbit.

294


LAMMER et al.

FLAMES spectrographs in Chile, as well as spectro�graphs at McDonald observatory.

The discovery of CoRoT�7b, the first small rockyexoplanet with measured radius and mass, and there�fore with a known density, has opened up a new era, inwhich the CoRoT extended mission and Kepler arenow playing a major role. While CoRoT has demon�strated that exoplanets can be observed via transitsfrom space, due to the mission design CoRoT cannotdiscover Earth�size exoplanets within the habitablezones of their host stars. This is a task where NASAsKepler satellite will take over.

The scientific objective NASAs Kepler satellitewhich was successfully launched on March 6, 2009 isto explore the structure and diversity of planetary sys�tems. The Kepler space observatory surveys a largesample of stars with the following main scientificgoals:

—Determination of the percentage of terrestrialand larger planets there are in or near the habitablezone of a wide variety of stars;

—Determination of the distribution of sizes andshapes of the orbits of these exoplanets;

—Estimate how many planets there are in multi�ple�star systems;

—Determine the variety of orbit sizes and planetreflectivity, sizes, masses and densities of short�periodgiant exoplanets;

—Identify additional planets of each discoveredplanetary system by using other techniques;

and—Determine the properties of those stars that har�

bor planetary systems.Kepler is a 0.95 m diameter telescope which has a

very large field of view of about 105 square degrees.The fields of view of most telescopes are less than onesquare degree. Kepler needs this large a field in orderto observe continuously and simultaneously monitorthe brightnesses of more than 100 000 stars during thenominal mission life time of about 3.5 years.

The design of the entire system is such that thecombined differential photometric precision over a6.5 hour integration is less than 20 ppm (one�sigma)for a 12th magnitude solar�like star including an assumedstellar variability of 10 ppm. This is a conservative, worse�case assumption of a grazing transit. A central transit ofthe Earth crossing the Sun lasts 13 hours. And about75% of the stars older than 1 Gyr are less variable thanthe Sun on the time scale of a transit.

The science case of the Kepler fits like that ofCoRoT into the discussed exoplanet roadmap stepsand supports also the objectives of the future ExoPTF�recommended NASA Space Interferometry Mission(SIM�Lite) and the Terrestrial Planet Finder (TPF�C/I) projects. Although these future missions will notre�observe the Kepler discoveries, the CoRoT/Keplerresults can be used for the identification of commonstellar characteristics of host stars for future planet

searches, for the definition of the volume of spaceneeded for the search. Based form the mission design,planet formation models and discovered exoplanets,the Kepler team estimated that the mission may dis�cover about 50 planets with the size of the Earth, about185 exoplanets where most of them have sizes of about1.3 REarth and more than 600 exoplanets with sizesaround 2.2 REarth. Kepler’s first discoveries of 4exoplanets in the hot Jupiter/Saturn domain, and onehot Neptune was announced at the American Astro�nomical Society in Washington DC, on January 4, thisyear.

However, both telescopes, CoRoT and Kepler tar�get rather faint stars, up to mV = 15 and beyond. Theirground�based follow�up, in particular in radial veloc�ity monitoring, is made difficult by this relative faint�ness. As a consequence, ground�based confirmationand mass measurements are restricted to the largest ofthe CoRoT and Kepler planets, which impacts defi�nitely the scientific return of these two missions. Incase Kepler will discover Earth�size planets within thehabitable zones of Sun�type stars the mass determina�tion will be very difficult.

PLATO: The Next Generation Exoplanet Transit Mission

ESAs PLATO mission is proposed as a next gener�ation exoplanet transit mission with the main focus todetect and by including follow�up programs to charac�terize exoplanets and their host stars in the solarneighborhood. The main differences betweenCoRoT/Kepler and PLATO will be its strong focus onbright stellar targets, typically with mV ~ 11, includinga large number of very bright and nearby stars, withmV ~ 8. Because of this PLATO would fit into the pre�characterization aim of rocky exoplanets close enough tothe Solar System. If this is possible future missions couldspectroscopically study the atmospheres of the discov�ered planets. The prime science goals of PLATO are:

—The detection of exoplanets of all kinds reachingdown to small, terrestrial planets in the habitable zone;

—The study of the host stars (age, activity, etc.);—The pre�characterization of the discovered

exoplanetary systems, planets + host stars;—The identification of suitable targets for future,

more detailed characterization, including a spectro�scopic search for biomarkers in nearby habitableexoplanets.

During ESAs assessment study as shown in Fig. 3,three concepts for the PLATO�telescope have beenstudied. In the first concept, the chosen solution has12 reflective telescopes with a field�of�view of about1800 deg2, and a total collecting area for each observedstar of 0.15 m2, while the second concept uses54 refractive telescopes with a field�of�view of 625 deg2,and a total collecting area for each observed star of0.29 m2. The third concept proposes a different



arrangement with 42 refractive telescopes. PLATO isplanned to be launched by a Soyuz 2�1b launcheraround 2017, which will inject the spacecraft in adirect transfer orbit and transfer the telescope to thesecond Lagrange point.

These goals will be reached by ultra�high precision,long (few years), uninterrupted photometric monitor�ing in the visible band of very large samples of (pre�selected) bright stars.

The obtained space�based data will be comple�mented by ground�based follow�up observations, inparticular very precise radial velocity monitoring,which will be used to confirm the planetary nature ofthe detected events and to measure the planet masses.Planetary rings and large moons around exo�Jupiter’sor exo�Saturn’s can also be detected by their modifi�cation on the shape and duration of the transit light�curve. For example, for a Saturn�analogue at 1 AUfrom the parent star, the ingress and egress take onehour for the planet and two hours for the ring. In addi�tion, the planet ingress (egress) starts (ends) steeperfor the planet than for the ring. Finally, the projectedinclination of the ring with respect to the planet’sorbital plane and the ring optical depth can be derivedfrom the transit shape, which provides valuable infor�mation for the formation and evolution studies of thesystem.

Several host stars of discovered exoplanets will beamongst the brightest. Therefore, they will be the nat�ural targets for atmospheric studies, either through:

—transmission spectroscopy; or

—reflection spectroscopic studies.

The second program of PLATO focuses on aster�oseismology and stellar evolution. It is planed that theinstrument will perform a detailed seismic analysis ofthe planet host stars, allowing a precise determinationof their radii, masses and ages, from which the radii,masses and ages of the exoplanets will be derived. Thiswill provide a complete characterization of theexoplanetary systems, including their evolutionarystatus. The obtained results will add to the knowledgeof planets related to the age of their host star, activity,etc. If one obtains atmospheric knowledge by follow�up observations one can study the role of the host star(age) activity to particular atmosphere species duringthe evolution of the planet in time.

To fulfill the whole program the mission relies onan extensive ground�based follow up programme.PLATO discoveries should be complementary withESOs 42 m E�ELT telescope. Phase�A studies of thelikely first generation suite of instruments are cur�rently underway. This includes the Exo�Planet Imag�ing Camera and Spectrograph (EPICS), which will beoptimized for visible and near�IR photometric, spec�troscopic and polarimetric observations. Interestingdiscovered exoplanets will be considered as prime tar�gets by E�ELT follow�up characterization observa�

tions and for other future space projects/program ded�icated to the search for bio�markers.

Asteroseismic data from PLATO will be used tomeasure the stellar masses and ages, to confirm andimprove the star’s radius already known from the Gaiamission, which will be discussed in the following Sec�tion, as well as to study the internal structure andinternal angular momentum of planet host stars.

Gaia

The ESA Gaia all�sky survey space mission, due tobe launched in Spring 2012, will monitor astrometri�cally, during its 5�yr nominal mission lifetime, all pointsources (stars, asteroids, quasars, extragalactic superno�vae, etc.) in the visual magnitude range 6–20 mag, ahuge database encompassing ~109 objects. Using thecontinuous scanning principle first adopted for Hip�parcos, Gaia will determine the five basic astrometricparameters (two positional coordinates α and δ, twoproper motion components μα and μδ, and the paral�lax ) for all objects, with end�of�mission precisionbetween 6 μs (at V = 6 mag) and 200 μas (at V = 20 mag).

Gaia astrometry, complemented by on�board spec�trophotometry and (partial) radial velocity informa�tion, will have the precision necessary to quantify theearly formation, and subsequent dynamical, chemicaland star formation evolution of the Milky Way Galaxy.The broad range of crucial issues in astrophysics thatcan be addressed by the wealth of the Gaia data is sum�marized by e.g., Perryman et al. (2001).

One of the relevant areas in which the Gaia obser�vations will have great impact is the astrophysics ofplanetary systems (e.g., Casertano et al., 2008), in par�ticular when seen as a complement to other techniquesfor planet detection and characterization (e.g.,Sozzetti, 2009). For multiple systems, a trade�off willhave to be found between accuracy in the determina�

ω

Fig. 3. Illustration of the three studied PLATO�telescopeconcepts. Right (first concept) 4 groups of 3 telescopes(brown) mounted on an angled optical bench. The deploy�able sunshield is shown in yellow/orange. Middle (secondconcept) 54 telescopes mounted on the tilted base plate.The sun shield is shown in blue. FEE boxes are visible atthe bottom. Each telescope has a hexagonal radiatorattached to the barrel segment which is shown in yellow.Right (third concept) telescopes mounted in groups on astaircase shaped optical bench (courtesy of the PLATOteam).

296


LAMMER et al.

tion of the mutual inclination angles between pairs ofplanetary orbits, single�measurement precision andredundancy in the number of observations withrespect to the number of estimated model parameters.It will constitute a challenge to correctly identify sig�nals with amplitude close to the measurement uncer�tainties, particularly in the presence of larger signalsinduced by other companions and/or sources of astro�physical noise of comparable magnitude. Finally, incases of multiple�component systems where dynami�cal interactions are important, fully dynamical New�tonian fits involving an n�body code might have to beused to properly model the Gaia astrometric data andto ensure the short� and long�term stability of thesolution (Sozzetti, 2005).

All the above issues could have a significant impacton Gaia’s capability to detect and characterize plane�tary systems. For these reasons, within the pipeline ofCoordination Unit 4 (object processing) of the GaiaData Processing and Analysis Consortium (DPAC), incharge of the scientific processing of the Gaia data andproduction of the final Gaia catalogue to be releasedsometime in 2020, a Development Unit (DU) hasbeen specifically devoted to the modelling of the astro�metric signals produced by planetary systems. The DUis composed of several tasks, which implement multi�ple robust procedures for (single and multiple) astro�metric orbit fitting (such as Markov Chain MonteCarlo and genetic algorithms) and the determinationof the degree of dynamical stability of multiple�com�ponent systems.

Gaia holds promise for crucial contributions tomany aspects of planetary systems astrophysics, incombination with present�day and future extrasolarplanet search programs. For example, the Gaia data,over the next decade, will allow us to:

—significantly refine of our understanding of thestatistical properties of extrasolar planets;

—carry out crucial tests of theoretical models ofgas giant planet formation and migration;

—achieve key improvements in our comprehen�sion of important aspects of the formation and dynam�ical evolution of multiple�planet systems;

—provide important contributions to the under�standing of direct detections of giant extrasolar planets;

—collect essential supplementary information forthe optimization of the target lists of future observato�ries aiming at the direct detection and spectroscopiccharacterization of terrestrial, habitable planets in thevicinity of the Sun; and

—will enhance our knowledge on potentialexoplanet host star parameters, which is important forasteroseismic studies yielding the age of the star forinstance.

RELEVANT PROJECTS IN ORBIT, DEVELOPMENT OR STUDY: SPITZER/HST,

WSU�UV, JWST, TESS, SPICA, SIM�LITE

The Hubble Space Telescope (HST) andSPITZER space telescope detected recently atmo�spheric species in the hydrogen�rich atmospheres of afew transiting hot gas giants with a resolution of about5. The telescopes can be used for transit spectroscopyby taking a photometric measurement of the exoplanetand its host star during the transit and later anothermeasurement when the star is occulting the exoplanet.By subtracting first signal from the second, theremained signal from the planet can be analyzed.Because the signal obtained from the exoplanet is veryfaint compared to that of its host star, such observa�tions demand a very high photometric stability overthe observing time. Theoretical models indicate thattransit spectroscopy may be possible for super�Earth’sif they orbit around M�type dwarf stars which arecooler and therefore fainter than our Sun.

The HST follower, James Webb Space Telescope(JWST), currently constructed by ESA/NASA andlaunched in 2014 is a large infrared telescope with a6.5�meter primary mirror. Originally planned forobservations related to star and planet formation, oneof its key scientific objectives will be the characteriza�tion of exoplanets. This capability was recently recog�nized after the recent observations by SPITZER andHST. The JWST has three instruments which are rele�vant for exoplanet characterization. The NIRCAMcovers wavelengths between 2–5 μm, the TFI 2–5 μmand MIRI 5–28 μm. By using the transit spectroscopymethod as described above, JWST will make also acontribution to the detection of atmospheric species inexoplanet atmospheres. There are model simulationsand plans to investigate the possibility that, if transit�ing super�Earth’s orbit nearby red cool, faint dwarfstars, atmospheric spectra, including bio�markers maybe obtained.

Hydrogen�rich gas giants or exoplanets withexpanded hydrogen thermospheres (Fig. 4) can bedetected in the Lyman�α line at 121.567 nm with a UVspectrograph, as neutral hydrogen atoms absorbLyman�α photons. This is visible as a dip in the light�curve of the transit signal. The presence of an extendedhydrogen cloud around a planet can be explained byseveral scenarios, depending on the composition ofthe atmosphere. Stellar wind produces additionalabsorption features, making it possible to distinguishbetween hydrodynamic, hot atom and stellar�windinduced mass loss and additionally observing stellarwind conditions at the location of extrasolar planets.

For instance the hot Jupiter HD209458b is anexoplanet found to transit the disk of its parent star.Observations have shown a broad absorption signatureabout the Lyman α stellar line during a transit, sug�gesting the presence of a thick cloud of atomic hydro�



gen around the HD 209458b (Vidal�Madjar et al.,2003; Holmström et al., 2008; Eckenbäck et al., 2010).

These Lyman�α observations compared with ther�mospheric modeling, including hydrodynamic expan�sion and out�flow models, photochemical producedhot planetary hydrogen atoms and stellar wind plasmainteraction modeling can be a useful diagnostic for:

—exomagnetospheric modeling;—for obtaining a better understanding of the ther�

mospheric�exospheric structure of hydrogen�richexoplanets; and

—for inferring stellar wind plasma propertiesaround the exoplanets location.

However, the HST is at present time the only UVspace observatory in operation and its follower theJWST does not have the capability to observe the UVuniverse. From all near future UV projects the Rus�sian�led WSO�UV space telescope is the best suited forthe observations of hydrogen�clouds around exoplan�ets after HST stops its operation in 2013. The WSO�UV is grown out the needs of the Astronomical com�munity to have access to the Ultraviolet (UV) range ofthe spectrum and is planned to be launched in 2012.The WSO�UV project consists at present of partnersfrom Russia, Spain, Germany, China, Ukraine, andKhazakhstan. It is an international space observatoryfor observation in UV spectral range (>100–350 nm)and it includes a telescope with primary mirror of170 cm and scientific instruments—imaging fieldcameras and 3 spectrometers (resolving power rangesfrom 2000 to 55000).

The WSO�UV illustrated in Fig. 5 incorporates aprimary mirror of 1.7 m diameter which is half of thecollecting area of the HST, but taking advantage of themodern technology for astronomical instrumentation,and of a high altitude, high observational efficiencyorbit. The WSO�UV will provide UV�optical astro�nomical data quantitatively and qualitatively compa�rable to the exceptional data base collected by theHST.

The science tasks of the WSO�UV space observa�tory will be related to the study of thermal and chemi�cal evolution of the Universe, including the search fordark matter, supernovae. Besides these astrophysicalthemes the WSO�UV will be a powerful tool for stellarphysics, the study of accretion discs, stellar winddetection related to stellar activity, and finally thestudy of the outer layers of exoplanetary atmospheres.The study with the WSO�UV of transiting exoplanetswill provide most of the information related to stellar�planet interaction discussed in the previous section.

Besides the ESA�studied European transit missionPLATO, a Transiting Exoplanet Survey Satellite(TESS) is planned in the USA by scientists at MIT, theHarvard�Smithsonian Center for Astrophysics, andNASA�Ames. The TESS satellite would use a set of sixwide�angle cameras with large, high�resolution elec�tronic CCDs so that an all�sky survey of transiting

planets around the closest and brightest stars could becarried out. The scientists involved in the study of theTESS project expect that the capabilities of this spaceobservatory are such that it could discover hundreds ofrocky exoplanets from Earth�size to super�Earth�sizes. Further TESS may detect giant exolanets at largeorbital radii with a photometric precision comparableto that of CoRoT with periods up to several tens ofdays around bright stars. TESS would have the capa�bility to do an all�sky survey to study bright nearbypotential exoplanet hosts. In combination with JWSTthe detected exoplanets could then be a very good can�didate for spectroscopic follow�up.

In the laboratory of the Russian Space ResearchInstitute (IKI) a small three�dimensional commonpath interferometer for achromatic nulling is currentlyinvestigated (Fig. 6) related to problems of stellarcoronography (Tavrov, 2008). In Bracewell’s method,a long�baseline interferometer increases the resolutionby using two telescopes. In this interferometer, thelight from the background on�axis source (star) has aphase shift by π radians and interferes with a phase dif�ference of π. At the same time, the light from the off�axis source (planet) interferes with another phase dif�ference, so that the off� axis source is attenuated onlyslightly and has a signal level sufficient for photodetec�tion. The suppression of the on�axis source (star)allows the observation of the off�axis source(exoplanet). The theoretical parameters agree withtheir laboratory experiment, in which the demon�strated achromatic nulling of the on�axis signal with anulling contrast of 10–3 in a visible spectral range300 nm in width.

Fig. 4. This illustration shows the size relation of exoplan�ets with extended hydrogen coronae around G�type starsand M�dwarfs, respectively (all radii to scale). On the leftthere is a Jupiter�like exoplanet with the size of 1RJup withan extended hydrogen thermosphere of 4.3 RJup orbiting aSun�type star, on the right an Earth�analogue with anatmosphere extending up to 10 REarth around an M�star(0.35 RSun and 0.55 RSun, respectively). In the observationof HD209458b the hydrogen thermosphere�exosphereresulted in a dip in the light curve of 15%. It is reasonableto assume that Lyman�α intensity can be similar for the M�star. Hence as a rough estimate, the occultation of the0.35 RSun M�dwarf by an Earth�size exoplanet would showa dip of about 6%, and 2.5% for the 0.55 RSun M�dwarf.

298


LAMMER et al.

In astronomical observations, exosolar planetshave a total brightness that is lower than the brightnessof a star by 6–10 orders of magnitude, depending onthe wavelength range, respectively, from the IR to thevisible. The theory is developed for the dependence ofthe nulling contrast due to partial spatial coherencecaused by the finite size of an extended source. Itshows that the method of nulling interferometry in the

existing implementation could be applied in the IR,where the required nulling contrast is 10–6 (Tavrov,2008). The method is planned to be tested on a 0.6 mtelescope which will be brought to the Russian seg�ment of the ISS around 2015. Besides various scien�tific goals the ISS T�600 telescope the three�dimen�sional common path interferometer for achromaticnulling will be tested related to trial methods of coro�

External

Baffle

Light protective

coverOptical

Bench

Cover of the

Instrumental

Compartment

Instrumental

Compartment

Secondary Mirror

Module

Tube Primary Mirror

Module

External

Instrumental Panel

Fig. 5. Illustration of the Russian WSO�UV telescope. The observatory includes a single 1.7 m aperature telescope capable of highresolution spectroscopy, long slit, low resolution spectroscopy, and deep UV and optical imaging. The Russian Federal SpaceAgency ROSCOSMOS has confirmed its readiness to lead the WSO�UV project so that the project was included in the FederalSpace Program of the Russian Federation and is planned to be launched around 2012 (http://wso.inasan.ru/).

v

z

PM

Fig. 6. Left laboratory test bed of the three�dimensional common path interferometer for achromatic nulling, which is plannedto be tested on a 0.7 m telescope (right) which will be installed at the Russian ISS segment around 2015.



nagraphic observation of exoplanets and other lowcontrast targets.

The SPICA (SPace Infrared telescope for Cosmol�ogy and Astrophysics) space observatory as illustratedin Fig. 7 is a proposed Japanese JAXA mission with alarge 3 m class infrared telescope where ESA wouldcontribute within Cosmic Vision 2010–2025 by a mis�sion of opportunity to the telescope assembly, a groundstation, and the science operations. The Europeanpart of the mission is the SAFARI instrument.

Besides astrophysical and cosmological sciencequestions (formation studies on the evolution of galax�ies) SPICA also addresses solar system and exoplanetscience relates issues related to:

—the formation and evolution of planetary sys�tems (dust and gas of planetary nebulae, protoplane�tary discs, etc.);

—the study of the ice�line in other star systems;

—detailed characterization of Kuiper Belt Objectsin the solar system and exosolar systems;

—atmosphere characterization by transit spectros�copy of known exoplanets in MIR (H2O, CH4, NH3,CO2, etc.).

The SAFARI�instrument, which is to be built by aconsortium of European institutes, with Canadian andJapanese participation, is an imaging Fourier Trans�form Spectrometer designed to provide continuouscoverage in photometry and spectroscopy from 34 to210 μm, with a field of view of 2′ × 2′ and spectral res�olution modes R = 2000 (at 100 μm), R ~ few hundredand 20 < R < 50. Four detector technologies are under�going development to meet these requirements, whereseveral of these detector technologies have alreadydemonstrated that they should be capable of deliveringthe required sensitivity for SAFARI and all are under�going a development program aimed at proving their

compatibility with the SPICA system—the finaldetector selection will be made by mid 2010.

Data obtained by SPICA has several solar systemscience connections for instance related to the chem�istry of protoplanetary discs, which is the major reser�voir of key species with prebiotical relevance, such asoxygen, ammonia (NH3), methane (CH4) or water(H2O) to be found later in exoplanets, asteroids andcomets. Within SPICA’s capabilities is the study of theice�lines in early planetary systems which will enhanceour understanding how the water is delivered to theEarth, maybe early Mars, early Venus and terrestrialexoplanets within habitable zones. Information of dustand mineralogy in planetary nebulae will be obtainedvia MIR/FIR mapping. SAFARI will study KuiperBelt analogues of other planetary systems out to150 pc, during the epoch at >10 Myr when the transitionform protoplanetary to debris discs occurs. If SPICA isapproved the satellite will be launched after 2015 withJAXA’s H�IIB from the Tanegashima Space Centre andis planned as a nominal three year mission with a goal of5 years orbiting at L2.

SIM�Lite is a NASA space�based differentialastrometry project that could be launched around2015–2020. It consists of a white light interferometerwith a small aperture that could measure astrometricsignatures of less than 0.6 micro arcseconds at nearbystars. This would allow seeing the deflection in theplane of the sky caused by any accompanying Earth�mass planets for about the 60–80 nearest solar�typestars.

EXOPLANET MISSIONS BEYOND 2020

By evaluating the present space projects andplanned project until 2020, by assuming no rise inbudgets on can see that the characterization ofexoplanet, including rocky Earth�like exoplanets is a

Fig. 7. Illustration of the JAXA/ESA SPICA telescope which may be launched around 2015–2017 (JAXA/ESA).

300


LAMMER et al.

complicated task, which is dependent of various smallto medium class space observatories which have tocompete with other non�exoplanet related space mis�sions. However, it is unlikely that there will be a spacemission before 2020 for direct characterization ofexoplanet atmospheres.

As mentioned before, the Euclid mission which isdedicated to map the geometry of the dark Universewas ranked scientifically high and is studied furtherwithin the Cosmic Vision 2010–2015 projects. It isplanned that the science return of Euclid can be fur�ther enhanced through an extension of the Euclid mis�sion after 2020 which can undertake additional surveysand use microlensing for the detection of low massexoplanets. This microlensing signal originates from atemporary magnification of a galactic bulge source starby the gravitational potential of an intervening lensstar passing near the line of sight, at a distance less thenthe Einstein ring radius. A planet which orbits the lensstar generates a caustic structure in the source plane.The source star transiting or passing next to one ofthese caustics will have an altered magnification com�pared to a single lens, showing a brief flash or a dip inthe observed light curve.

The duration of such planet lensing anomaliesscales with the square root of its mass, lasting typicallyone hour for Mars�mass, a few hours for Earth�mass,and up to 2–3 days for Jupiter�mass planets. TheEuclid science team plans a 3�month extension of thenominal mission period for undertaking a uniquemicrolensing survey of the Galactic Bulge, so thatexoplanets with masses > Mercury can be detected.Euclid has high angular resolutions which will

together with the uninterrupted visibility and NIRsensitivity, be ideal for such imaging capabilities. Theywill provide detections of microlensing events using assources G and K stars for rocky exoplanets down to0.1–1 MEarth from orbits of 0.5 AU. It is expected thatsuch a space�based microlensing survey is a good wayto enhance our understanding of the nature of plane�tary systems and their host stars, which is required tounderstand planet formation and habitability.

Besides the microlensing capability of an extendedEuclid mission exoplanet projects related to spectro�scopically characterization are studied. The SuperEarth Explorer Coronagraphic Off�Axis Space Tele�scope (SEE�COAST or SEE, Fig. 8) was proposedduring ESAs Cosmic Vision 2010–2025 programme asa M�class project but was not selected by ESAs AWGfor further studies such as the exoplanet transit missionPLATO. SEE�COAST or a similar mission could beaimed for direct detection and characterizingexoplanets from the super�Earth (~5 Earth masses) togas giant regime. Such missions would be dedicated toinvestigate and study star systems known to haveexoplanets. Given the rapid advances in the methodsemployed to find exoplanets which can be character�ized by a SEE�COAST�type mission, mainly byground based RV and astrometric measurements sev�eral interesting target planets should be observable.

SEE�COAST as shown in Fig. 8 consists of a spacetelescope, a coronagraph to suppress the starlight anda spectropolarimeter to take full advantage of theinformation embedded in the light that is reflected bythe exoplanet. The photons from the exoplanets willbe submitted to an extensive analysis which shouldgive as much information as possible about the inves�tigated targets:

—spatial information from the imager;

—near�infrared spectral fluxes from the IntegralField Spectrograph;

—visible spectral fluxes and polarization from thehigh�precision polarimeter.

All that can be learnt from the faint exoplanet sig�nal will be acquired to an unprecedented level of high�contrast imaging spectro�polarimeter. One may expectthat a SEE�COAST�type mission may belong to thefirst generation of direct characterization missions forexoplanets (Fig. 9).

This first generation is expected to be in the 1.5–2 mcoronagraph class which could study atmospheres ofgiant exoplanets, Neptune�class and even super�Earthatmospheres (e.g., Schneider et al., 2009). After 2020these missions may be followed by a generation of aninterferometer (Cockel et al., 2009, Lawson et al.,2009), an external occulter (Glassman et al., 2009), alarge 8�m class coronagraph (visible), a Fresnel Inter�ferometric Imager (Koechlin et al., 2009) or a 20 msegmented coronagraph which would resample asuper�JWST for the NIR (Lillie et al., 2001).

Fig. 8. Illustration of the SEE�COAST space observatory,which is designed for direct characterization of exoplanetatmospheres. One may expect that the first generation ofsuch type of missions may be developed after 2020.



The characterization of exoplanet atmosphereswith these 2020+ space observatories will be focusedon spectroscopy and polarimetric approaches. Addi�tionally to the detection of atmospheric gases, thepolarimetric approach could also be used for the studyof clouds, surface, rings, etc. (Stam, 2008).

SEARCH A FUTURE SPACE MISSION CONCEPT?

The study of a future space mission concept withthe name SEARCH originated during the FFG�ESA�ESO�ISSI�Austrospace sponsored Summer School inAlpbach, Austria between July 21–30, 2009, whosetheme was Exoplanets: Discovering and Characteriz�ing Earth Type Planets, and further developed duringa Post�Alpbach workshop by an international team ofyoung European scientists and former SummerSchool participants at the Space Research Institute ofthe Austrian Academy of Science in Graz, Austria theweek before the ESF Exploratory workshop was held.The SEARCH mission concept is intended to study

the diversity of terrestrial exoplanets by using spectro�polarimetry (Bühl et al., 2010).

Since the host star’s light scattered from anexoplanet is going to be polarized to a certain degree,depending on surface and atmospheric features, polari�metric measurements contain valuable information onthese characteristics not accessible by other methods.Examples are cloud coverage, cloud particle size andshape, ocean coverage, atmospheric pressure amongothers. Also the change in the degree of polarizationover one orbital period contains valuable informationon the orbital inclination, which is not accessible byradio velocity measurements. By combining thismethod with a spectral measurement, it should be pos�sible to characterize the atmospheric composition andto detect molecules like H2O, O2, O3, NH3 and CH4.

In order to achieve these ambitious goals two mainobstacles have to be overcome, being the high contrastratio between the exoplanet and its host star and theneed to spatially resolve these two with the spacecraft’stelescope. To meet those two requirements, newdesign concepts have been developed an analyzed.

Transit spectroscopySPITZER/HST, JWST, SPICA

Transits (space�based)TESS

AstrometrySIM�Lite

Super EarthExplorer,

Coronographs,External occulter,

Interferometeretc.

CoRoT, Kepler Gaia PLATO2010 2012 2014 2016 2018 2020

Fig. 9. Illustration of orbiting developed and planned S� and M�class exoplanet�related space missions between 2010–2020. Onecan see that during the next ten years the characterization of exoplanet atmospheres will be a complex and time consuming inter�play between transits, astrometry and transit spectroscopy. The current budgets available to the space agencies do not allow a tech�nologically feasible direct atmosphere characterization space mission. It seems that direct characterization space missions willnot be developed before 2020–2025.

302


LAMMER et al.

The proposed mirror is an f/1 parabolic mirror withelliptical rim the size of 9 × 3.7 m2 in a Cassegrain lay�out. It is cut in half and folded towards the secondarymirror to fit into Ariane 5 as illustrated in Fig. 10.Thus, with the SEARCH�concept problems regardingthe symmetric distribution of weight at launch can beovercome. Also the on axes�configuration signifi�cantly decreases the polarization losses introduced bythe system. This design allows for an angular resolu�tion high enough to resolve planets as close to its hoststar as 0.5 AU in a distance of 10 pc and as close as1.4 AU in a distance of 30 pc, being able to actuallycharacterize Earth�type exoplanets in a significant tar�get sample. Given the possibility to overcome techni�cal problems in the manufacturing of such large mir�rors, it is thinkable to launch a 20 × 3.7 m2 mirrorwithin an Ariane 5 rocket. The mirrors surfacesmoothness is crucial to the quality of the optical sys�tem. Since it is not possible to meet the requiredsmoothness over the whole area of the mirrors, activeoptics has been introduced correcting the wave frontaberrations due to deviations on the mirror surface.

Regarding contrast ratio, it has been shown, thatpolarimetry itself can reduce the contrast ratiobetween host star and planet by 5 orders of magnitude,

because of the host star’s light being almost completelyunpolarized. For the mission discussed, a half�wave�achromatic four quadrant phase mask can be chosenas both, a coronograph and a polarimeter. In additionto that, the use of an integral field spectrograph is pro�posed for separation of light from the star and theplanet as well as the reduction of speckle noise. It isclear that there are further technological develop�ments to be made before a mission concept likeSEARCH can be realized. Nevertheless, since nearlyall of those are key developments for other planned oralready scheduled space missions, the SEARCH con�cept may be able to use these developments to achievethe ambitious goal of characterizing Earth�like planetsbeyond 2020.

PRESENT AND FUTURE GROUND BASED EXOPLANET PROJECTS

Besides the before mentioned space�basedexoplanet projects there exist many ground�basedexoplanet programs dedicated to Radial Velocity (RV)surveys/observations, transit searches, etc. where wecan only mention a few of them. From the more than400 exoplanets, more than about 80% were detected

Secondarymirror

Primarymirror

Bus

Sun shield

Fig. 10. Illustration of the SEARCH concept with its folded 9 × 3.7 m2 mirror which fit well into an Ariane 5 rocket. Bottom leftthe SEARCH team at the Space Research Institute (IWF) of the Austrian Academy of Sciences during the Post Alpbach workshop(Nov. 24–29, 2009), where they developed this mission concept.Key: 1. Secondary mirror; 2. Primary mirror; 3. Bus; 4. Sun shied



by the RV�method, mostly of them are gas giants,about a dozen are hot Neptune’s and a handful ofsuper�Earth’s. From this fact one can see that theground�based exoplanet programs are important forexample for the determination of the constraints onthe exoplanet mass function, and orbit distribution.

The most prominent present day RV�telescopes areCoralie, Sophie, HARPS, HIRES, Lick, and AAPS.These instruments are capable of long term precisionstudies with RVs of < 1 m s–1, allowing the detection ofNeptune’s and super�Earth’s on short orbital periodsand gas giants on long periods up to 10 years. Around2014, NAHUL and GTC, SPIROU and CFHTshould improve the exoplanet detection limit to about1 m s–1 around cool M�type dwarf stars.

Several instruments are being planned for largetelescopes currently in operation. Specifically, thenext generation of ultra high precision RV�instru�ments can on a dedicated 8 m telescope, take the pre�cision currently available on telescopes like the ESO3.6 m + HARPS combination (0.5–1 m s–1) and mayimprove it by a factor of 10. The main problem is theactivity of the target stars which demand more or lesscontinuous coverage of the whole phase of the orbitalrevolution of a planetary candidate and, in the case oflow mass exoplanets like super�Earth’s, many periods.However, specially developed telescopes and instru�ments will carry the present day RV�studies into a newdomain of low exoplanet masses.

The ESPRESSO and VLT may detect Earth�massexoplanets within the habitable zone of low mass Mand K stars with a velocity of about 10 cm s–1. Futureground�based RV programs such as CODEX and theELT may reach the detection of Earth�mass exoplan�ets within the habitable zones over spectral types M,K, G and F around 2020. If space observatories likeTESS or PLATO which are dedicated to detect suchlow mass exoplanets close to our solar system areapproved, the ground based RV�follow up with theseinstruments will deliver the masses of the discoveredtransiting rocky exoplanets with a high accuracy.

Besides the RV�method, projects liked the recentlystarted MEarth�project in the USA, which is a photo�metric ground�based survey of about 2000 nearest M�dwarfs are also established. The MEarth�project withan accuracy of <5 × 10–3 mag, is optimized for tosearch for transiting super�Earth’s in the habitablezone of close M�dwarfs. The project consist of a suiteof eight amateur�sized telescopes with 40 cm diametermirrors, each with a sensitive CCD light detector thatmeasures the near�infrared brightness in wavelengthrange between 700–900 nm of a star. In case thebrightness dims for about 60 minutes and repeats itsdimming periodically over days and weeks, anexoplanet candidate is discovered, which can be con�firmed after the mass determination via a RV follow�up. The MEarth�project discovered recently a sub�Uranus/super�Earth�type planet with the size of about2.7 Earth�radii with an orbital period of 1.6 days

around the small, faint star GJ 1214 (Charbonneau etal., 2009). In Europe the WTS/UKIRT survey will tar�get a large sample of low�mass stars, searching fortransiting rocky planets with periods of a few days.

Another European project related to the detectionof exoplanets around very low mass stars uses the pre�cision of measurements in the near infrared which iscompared to optical wavelength from different instru�ments (ESO VLT/UVES, Keck/HIRES) (Reiners andBasri, 2010; Reiners et al., 2010). It shows that forearly ~M stars only no advantage is existent. From~M4 type stars on, the near Infrared gains in precisiontowards cooler types. Optical together with near Infra�red high precision spectroscopy will provide a power�ful tool for the search for exoplanets orbiting very lowmass stars.

In the Russian Federation a project of exoplanetobservations is planned for the 2010–2014 period,with a new 2 m telescope (observatory Terskol, Fig. 11)and with a participation of the Crimea astrophysicalobservatory (Ukraine). Within this project knownnon�transiting exoplanets will be observed by means ofthe polarimetric method, looking for their tangentialtransits, and using the experimental and theoreticalmodels for inferring more data from these objects(Ksanfomality, 2007).

The polarimetric search method has been testedexperimentally for this purpose; the necessary astro�nomical observations and their processing have beenperformed. The results obtained allow one to assertwith caution that the suggested method yields positiveresults and can be of use both in searching and charac�terizing exoplanets and refining their masses. The highcorrelation between the polarization variations andthe revolution period of an exoplanet would suggeststhat the angle between the orbital plane of the planetand the observer’s direction is small (sini ≈ 1). Thisallows refining the exoplanet mass, since the parame�ter Msin i turns into М if the effect is actually related toa tangential transit of the exoplanet’s comet�like tail.

Single aperture imaging is another technique whereinstruments with or without coronagraphs related todirect detection surveys on the VLT, Gemini, Keck,and HST are planned. Future planet finder instru�ments on 8�m class telescopes on the VLT and GeminiS./Subaru, such as SPHERE, GPI, HiCIAO areplanned to be in operation in the near future (2010–2011). The main observations with these instrumentsare dedicated for spectral characterization of selfluminous exosolar gas giants. In the visible, theSPHERE instrument is capable to detect irradiatedgas giants with R > 1 RJup, at about 1AU around nearbybright stars.

Ground�based astrometry projects on large tele�scopes like with FORS2 instrument on the VLT canreach typically 100 arcs over a few years necessary todetect exosolar gas giants around late M�type stars andNeptune�mass objects at brown dwarfs. One canexpect that future astrometric facilities are based on

304


LAMMER et al.

the use of adaptive optics and imaging cameras at largeground�based telescopes.

Several ground�based surveys related to micro�lensing observation are currently on�going and havebeen successful in the detection of the first super�Earth’s in orbits of very distant stars. The micro�lens�ing method appears to have significant capability asthe technology evolves.

Several large facilities are being planned for thenear future. Based on adaptive optics and segmentedtelescopes, examples are the Thirty Meter Telescope(TMT), with an 30 m effective aperture, in the USAand in Europe the 42 m European Extremely LargeTelescope (E�ELT). Operating from wavelengthsranging from UV to IR, science addressed by theselarge instruments include besides star� and planet for�mation, cosmological and extra�galactic research alsothe observation of exoplanets. There are currently fourE�ELT instruments for the characterization ofexoplanets under study:

CODEX: The accuracy of the COsmic Dynamicsand Exo�earth experiment, CODEX’s radial velocitymessurement accuracy will be about 2 cm/s, whichwill allow to detect Earth�mass exoplanets at 1 AU ifthey orbit on Sun�like stars with low activity;

EPICS: The Exoplanet Imaging Camera andSpectrograph, EPICS, is an optical/NIR planetimager and spectrograph with extreme adaptive opticswhich will detect transiting “super�Earth” planetsaround K and M�stars which are brighter than about

10 mag detected with PLATO would also be detectablewith EPICS. With regard to young, forming exoplan�ets, it will be possible to study the early evolutionwhich will lead to a better understanding of the initialmass function of such objects (see Fig. 12).

Besides CODEX and EPICS two other instru�ments, namely SIMPLE and OPTIMOS�EVE arealso studied for the E�ELT. SIMPLE will have thecapability to observe atmospheres of exoplanets in thewavelength range of 0.8–2.5 μm and OPTIMOS�EVEwill be dedicated for RV�surveys of extragalaticexoplanets in the optical and IR channels.

CHARACTERISATION OF TARGET STARS AND EXOPLANET ENVIRONMENTS

Our knowledge regarding the discovered exoplan�ets is directly related by our knowledge of the parentstar. The stellar X�ray and EUV (XUV) radiation andthe stellar plasma outflow constitute a permanentforcing of the upper atmosphere of the exposedexoplanets and therefore can affect the atmosphericevolution and even habitability. The main effect ofthese forcing factors is to ionize heat, chemicallymodify, expand and slowly erode the upper atmo�sphere throughout the lifetime of an exoplanet.

The host star and its related activity can influencethe ability to detect and measure exoplanet parame�ters. This can result in systematic errors:

Fig. 11. The Russian Terskol telescope in the northern Caucasus mountains is planned to test the characterization of known mon�transiting exoplanets by a polarimetric method.



—in indirect methods, all we see is the starlight(activity, binarity/rotation);

—in direct methods, there can be challenges todetectability (zodiacal light, binarity);

—calculated planetary properties (mass, radius)are relative to those of the star (in a linear manner).

By ultimately determining the intrinsic propertiesof exoplanets, their host star is the overwhelminglylarger source of energy. The stellar radiations andplasma environment (winds and CMEs) criticallyaffect the composition, thermal properties, atmo�sphere evolution and even the mere existence of aplanetary atmosphere, or its water inventory.

The physical and fundamental properties for targetstars are, the stars mass, radius, chemical compositionand age. These properties can be determined by thefollowing methods:

—calibrations (from binaries, clusters, etc);—stellar evolution models;—asteroseismology;—age: kinematics, asteroseismology, activity,

chemical abundances (Li, Be), theoretical models.—the radiative properties of the targets can be

studied if one obtains a detailed spectral energy distri�bution from X�rays to IR, and radio. Other importantstellar parameters are related to the time variability ofthe stellar emissions. Such processes can vary from:

—minutes to hours: micro variability, flares, massejections;

—days: spot modulations, spot evolution; years:spot cycles;

—centuries: Maunder�like minima;—to billions of years: rotational spin down.

Short�term variations up to years can be studied byestablishing time�series with photometry. For longertimescales observations of stellar proxies or stars of thesame spectral class with different ages are the bestoptions.

Stellar Radiation and Plasma Environment as Function of Age

In general, the boundaries of the habitable zonechange throughout the star’s lifetime as the stellarluminosity and activity evolve (Lammer et al., 2009).Because the evolution is different for different star�types, and furthermore depends on their age and thelocation of the habitable zone around the host star onecan expect that the atmospheric evolution of Earth�like exoplanets is strongly coupled with the evolutionof the host star. This fact makes the type and the age ofexoplanet host stars very important.

From that point of view the PLATO mission con�cept is an interesting one, because the resulting highquality light curves will be used for measuring thecharacteristics, and on the other hand to provide aseismic analysis of the host stars of the detected plan�ets, from which precise measurements of their radii,masses, and ages will be derived.

Activity in late�type stars (i.e., spectral types G, K,M) has been the subject of intense studies for manyyears by various satellites such as: ASCA, ROSAT,EUVE, FUSE and IUE. The most important physicalphenomena of stellar activity include modulations ofthe stellar photospheric light due to stellar spots, inter�mittent and energetic flares, coronal mass ejections(CMEs), stellar cosmic rays, enhanced coronal X�rays, and enhanced chromospheric UV emission. For

Field Plate in reconfiguration position

Robot positioner

Movingplatform

Fixed raisedplatform

Fig. 12. Illustration of the baseline design of the Exoplanet Imaging Camera and Spectrograph (EPICS) on the left and OPTI�MOS�EVE on the right (ESO).Key: 1. Field Plate in reconfiguration position; 2. Robot positioner; 3. Moving platform; 4. Fixed raised platform

306


LAMMER et al.

solar�type stars this has been studied with high accu�racy within the “Sun in Time” project, where a sampleof single nearby G0–V main sequence stars withknown rotation periods and well�determined physicalproperties, luminosities and ages which cover 100Myr–8.5 Gyr has been analyzed. From these data onecan conclude that the solar integrated flux between 0.1�120 nm, 3.5 Gyr ago, was higher by a factor of 6, andup to 100 times more intense than that of todays Sunduring the first 100 Myr after its arrival at the zero�agemain�sequence (ZAMS) (Ribas et al., 2005).

This activity–age relation indicates that lower massstars spend more time in this highly active but satu�rated phase before beginning their activity decay. Inparticular, solar�type stars stay at saturated emissionlevels until they age to ~100 Myr, and then their X�ray,SXR luminosities rapidly decrease as a function of agefollowing a power law relationship (Ribas et al., 2005).

But low mass M�dwarfs, on the other hand, havesaturated emission periods up to 0.5–1 Gyr and possi�bly longer for late�type M stars (Scalo et al., 2007).After that the luminosity decreases in a way similar tosolar�type stars. Therefore, one may expect that theatmospheres and their evolution will be stronger—longer—affected at lower mass stars compared tomore massive solar like G�type stars of F�type stars.

Stellar winds and CME plasma outflows have alsoimportant implications for the stellar and exoplane�tary environments. The outflowing stellar plasma canlead to non�thermal losses of planetary atmospheresexposed to it, especially non� or weakly magnetizedones. Due to tidal locking and slow rotation the mag�netic dynamos of rocky exoplanets within orbits oflower mass stars may be weaker compared to fast rotat�ing planets like the Earth. Additionally close�inexoplanets are exposed by dense plasma flows close totheir host stars.

During the last years several indirect methods forstudying tenous stellar winds of Sun�like stars havebeen evaluated. The method which yielded the largestnumber of mass loss estimates so far was the search forastrospheric absorption in the region where the stellarwind meets the local interstellar medium and neutralhydrogen is formed via charge exchange. This givesrise to an absorbtion of the blue side of the stellarLyman�α line. The amount of absorption is propor�tional to the stellar wind ram pressure and thereforeyields estimates of the mass loss rate (Wood et al.,2002, 2005). By applying this method with the HubbleSTIS spectrograph the mass loss rates of about a dozensolar�like stars and cooler stars have been derived.Depending on the age of the observed star, the massloss rates are in the order of <0.2–100 times thepresent solar rate.

One needs clearly more observations in the futurewith HST, WSO�UV or IXO, etc. Although stellarwind observations are difficult to obtain, but if wedon’t understand how the stellar plasma outflowevolves with the age of the star after its arrival at the

ZAMS one will never fully understand its role in theevolution of planetary atmospheres and even habit�ability.

There are also other wavelength ranges whichinclude phenomena which are known signatures ofCMEs on the Sun. An analysis of tens of solar CMEsand temporal correlated decameter type II bursts indi�cates, that every solar decameter type II burst of thisstudy is correlated with a CME, but not every CME iscorrelated with a decametric type II burst. We areusing this context to search for stellar analogues ofthese decametric type II bursts on active late�typemain�sequence stars, especially on M�stars, due to thebefore mentioned effect on exoplanetary atmospheres.

Due to this analysis a project was initiated toobserve such decametric type II bursts on active Mdwarfs with the present time World’s largest decameterarray, the UTR�2 (Ukrainian T�shaped Radiotele�scope 2nd modification) shown in Fig. 13 and hostedby the Institute of Radio Astronomy in Kharkov of theUkrainian Academy of Sciences. The huge effectivearea of the UTR�2 is more than 150000 m2 large andensures a sensitivity of about 1 Jy or less depending onthe observing conditions. The instrument has a multi�beam capability of five simultaneously operatingbeams. Further a selection of five digital back�ends isavailable from 1024 up to 16384 frequency channels.All of them perform FFT (Fast Fourier Transforma�tion) in realtime.

First results were obtained during an observationalcampaign which took place in February of 2007 at theUTR�2. The target for this campaign, AD Leo, wasselected due to its young age of about 200 Myr, a lgLXvalue of 28.8, the close distance of 4.7 pc, and ofcourse suitable coordinates. Two digital back�endswere installed on beam 3 and 5 (beam 3 is pointing atthe target and beam 5 is pointing one degree apart forthe investigation of the background). The integrationtime was set to 100 ms in a bandwidth of 18–30 MHz.

During more than 60 hours of ADLeo observations atthe UTR�2, many structures could be detected in thedynamic spectra. After careful analysis only a handfulshows a high probability of being of stellar origin, accord�ing to their only appearance in spectra of beam 3 and fur�ther only appearance in the main lobe of the antenna pat�tern. So far structures which show a slow frequency drift(type II) could not be detected, instead structures with ahigh frequency drift (1–2 MHz s–1) similar to solar deca�meter type III bursts were detected.

A possible interpretation of the non�detection ofstellar analogues of solar decameter type II burstsmight arise from the difference of M� and G�starsatmospheres (temperature and spatial scales) and dueto the difference of convective layers.

Besides investigations of stellar plasma events, thedetection of radio emission in certain wavelengthswould convey information on the rotation of exoplan�ets, and the existence and intensity of a planetary mag�



netic field. The latter factors are important ingredientsfor studies of planetary habitability. Using knownplanetary characteristics (mass, radius, age, orbit, dis�tance, etc) Grießmeier et al. (2007) estimated the max�imum emission frequency and the radio flux for allexoplanets known as of 13.1.2007. Figure 14 gives abrief update, including all exoplanets that were discov�ered since.

The results are visualized in Fig. 14. For eachexoplanet individually, the expected maximum emis�sion frequency and the estimated maximum radio flux(maximum of the three models: magnetic energymodel, CME model, kinetic energy model) is given.The predicted planetary radio emission is denoted byopen triangles (two for potentially locked exoplanets,otherwise one per exoplanet). The typical uncertain�ties (a factor of 2–3 for the maximum emission fre�quency, and approx one order of magnitude for theflux) are indicated by the arrows in the upper right cor�ner. Due to the relatively faint signal, large antennaarrays are required. For this reason, this kind of obser�vation can only be performed by ground�based radio�telescopes as the UTR�2 shown in Fig. 13 or the futureLow Frequency Array (LOFAR). As the terrestrialionosphere is reflective for low frequencies, frequen�cies below 10 MHz are not observable from theground, which gives the lower limit for the frequencyrange of interest. Figure 14 shows that the upper limitof that frequency range appears to be around ~200MHz.

The expected sensitivity of new and future detec�tors (for 1 h integration and 4 MHz bandwidth, or anyequivalent combination) is shown for comparison.

The limit of the confusion effect sensitivity of UTR�2for the continuum point radio source (25 MHz) isabout 1 Jy. However, the sensitivity without the confu�sion effect is about 10 mJy. Horizontal line at 10 mJy:upgraded UTR�2, sloped lines: low band and highband of LOFAR. The instruments' sensitivities aredefined by the radio sky background. For a given

Fig. 13. The World’s largest decameter array operated by the Institute of Radio Astronomy in Kharkov of the Ukrainian Academyof Sciences is used also for the search of radio signals originated in exoplanet magnetospheres and decametric type II bursts whichare related to stellar CMEs.

101

10–1

10–3

10–5

10 MHz

10–7

100 MHz 1 GHz

Φ [

Jy =

10–

26W

m–

2 Hz–

1 ]

f1 MHz

Fig. 14. Estimated the maximum emission frequency andthe radio flux for all exoplanets currently known (updatedfrom Grieβmeier et al., 2007).

308


LAMMER et al.

instrument, a planet is observable if it is located eitherabove the instrument’s symbol or above and to its right.

Up to ~30 exoplanets should be observable usingeither of these instruments. It can also be seen that themaximum emission frequency of a considerable num�ber of exoplanets lie below the ionospheric cut�off fre�quency 10 MHz, making ground�based observation ofthese planets impossible. The figure also shows thatthe relatively high frequencies of the planned LOFARhigh band are probably not very well suited for thesearch for exoplanetary radio emission. These instru�ments could, however, be used to search for radio�emission generated by unipolar interaction betweenexoplanets and strongly magnetized stars.

USING VENUS, EARTH AND MARS AS EXOPLANET PROXIES WHEN THEY

EXPERIENCING EXTREME SOLAR EVENTS

Exoplanet science has a strong link to Solar Systemscience where many important data and expertise havebeen collected during the past decades. By establishinga coordinated study of the behaviour of the upperatmospheres, ionospheres, magnetospheric environ�ments and thermal and non�thermal atmospheric lossprocesses of Venus, Earth, and Mars during extremesolar events important knowledge could be establishedrelated to exoplanet atmospheres orbiting withinextreme steller environments.

Such studies can also serve as a proxy for the influ�ence of the active young Sun (G�star) with implica�tions for the evolution of planetary atmospheres (solarsystem and exoplanets), water inventories and habit�ability. Extreme events involve enhanced solar EUVand X�ray radiation, neutron fluxes, coronal massejections (CMEs) and related intense solar pro�ton/electron fluxes (e.g., SPEs), auroral phenomena,magnetic storms, etc. Responses of planetary atmo�spheres include: thermospheric and ionospheric den�sity variations, changes in atmospheric compositionincluding ozone depletion leading to changes in heat�ing/cooling, temperature and wind perturbations,photochemistry, collisional excitation, deactivationand cooling due to IR�, optical and UV�emissions,magnetospheric compression, enhancement of sec�ondary particles, etc. Studies of the evolution of thespectral irradiances (X�ray, EUV, UV) of solar�typestars of different ages will be used as a proxy for recon�structing the history of the Sun’s radiation output.Complementary information concerning solar massloss (solar wind) will be derived from studies of theenergy distributions of flare related CMEs during lowand high solar activity by estimating CME relatedsolar mass loss to the early stage of the solar systemusing solar proxies.

There are many space�based data available. Ener�getic particle data (40 keV, several 10s MeV) recordedat L1 over eleven years by the LION instrument onSOHO, data which will be obtained by the WAVE

1

instrument on board of STERO, particle, near�Earthproton fluxes can be used from GOES satellites, mag�netic field and electromagnetic data from the Phobos2 mission to Mars and its Moons, plasma data fromASPERA�3 (Mars Express/MEX) and ASPERA�4/magnetic MAG data (Venus Express/VEX), CLUS�TER and Double Star, ENA data from MEX, VEX,and NUADU (Double Star).

There are many atmospheric data available for CO2rich atmospheres beginning with the Venera missions,MEX, VEX, and other missions. Density and tempera�ture changes in the Earth’s thermosphere during extremesolar events could be analyzed by using low perigee satel�lite data (e.g., CHAMP, GOCE). Short/medium dura�tion ionospheric disturbances can be monitored by GPSand GLONASS transmissions revealing large variationsin the northern hemisphere total electron content(TEC). Europe’s GOMOS/Envisat instruments provideobservations of both short�term (days) and long�term(months) atmospheric effects caused by extreme solarevents such as SPEs.

GOMOS which was developed at the FMI mea�sures e.g. ozone, NO2, and NO3 in the stratosphere andmesosphere. Data obtained by the Millimetre�waveAirborne Receivers for Spectroscopic CHaracterisa�tion in Atmospheric Limb Sounding (MARSCHALS)project will be utilized to analyze the chemistry andcomposition in the Earth’s thermosphere. Solar andstellar data needed for the reconstruction of the his�tory of G�star (solar) radiation and particle emissionsare available as discussed before from observationsobtained aboard the SOHO, STEREO, ASCA,ROSAT, EUVE, FUSE, and IUE a satellites. Newspecific observations will be obtained by XMM/New�ton, Chandra and Suzaku. Feasibility studies toobserve the stellar hard non�thermal emission withSymbol�X will be performed.

Especially studies which set the Earth in contextwith Earth�like exoplanets under extreme stellar con�ditions could also use ground�based observations,which may include radio tomographic monitoring ofthe TEC (Total Electron Content). This can allowreconstruct the 2�D structure of the terrestrial iono�sphere/thermosphere during extreme solar events.Parameters of the ionosphere can be determined byusing the EISCAT radar network and magnetometerchain in northern Europe.

There are also many theoretical codes available forthe analysis and study of exoplanet�proxy events atVenus, Earth and Mars. Test�particle/Monte Carlo,MHD, hybrid, diffusive�photochemical, thermal bal�ance, and global circulation models are available for:investigating ionized and neutral atmospheres, solarwind/planetary interactions, and particle energy dep�osition in the upper atmospheres. The 1�D SodankylaIon and Neutral Chemistry Model will be used tostudy the ionospheric�atmosphere interaction pro�cesses, caused by e.g. proton/electron precipitation or



solar X�ray flares, which lead to changes in atmo�spheric composition.

ESTABLISHING A WELL COORDINATED EXOPLANET COMMUNITY

At the present, scientists do an excellent job in thefield of exoplanet discoveries and research. Many sci�entific studies are carried out in various institutes,research groups and single researchers. In the nextstep, exoplanet research needs to be more seen withinthe scientific community and the public. We think thatinstitutions such as the ESF together with existingexoplanet related science teams like existing ISSIteams, or networking research projects such as theGerman�based Helmholtz Alliance project PlanetaryEvolution and Life and working groups within the EUFP7 funded Europlanet project (especially Na1 andNa2) can be very useful supporters to build up a wellcoordinated and structured exoplanet research infra�structure and community in Europe.

ACKNOWLEDGMENTS

The authors acknowledge the support by tire ESF,and the International Space Science Institute (ISSI,Bern, Switzerland) and the ISSI teams Evolution ofHabitable Planets and Evolution of Exoplanet Atmo�spheres and Their Characterization. The authors alsoacknowledge also support from the Europlanet Net�working activity Na1 (Observational InfrastructureNetworking), and Science Networking Na2 workinggroup (WG4 and WG59 activities. Furthermore, weacknowledge support by the Austrian Academy of Sci�ences, Verwaltungsstelle für Auslandsbeziehungen,and by the Russian Academy of Sciences (RAS), Rus�sian Federation. We acknowledge the Austrian FWF(Wissenschaftsfond) and the Russian Fund for BasicResearch (RFBR) for support via the projects P20145�N16, FWF I 199�N16 and RFBR grant no. 09�02�91002. V. Eybel and S. Eggl also acknowledge supportfrom the FWF under projects P18930�N16 andP20216. We acknowledge also support from the Aero�nautics and Space Agency, Austrian Research Promo�tion Agency (FFG). Furthermore, we acknowledgethe Helmholtz Association through the research alli�ance Planetary Evolution and Life. Finally weacknowledge the following co�sponsors of this ESFWorkshop which are the University of Graz, Touris�musverband Bad Gleichenberg, Gemeinde BairischKölldorf, Stadtgemeinde Feldbach, RaiffeisenbankBad Gleichenberg.

REFERENCES

Bühl, J., Doherty, S., Eggl, S., et al., Opening a New Win�dow to other Worlds with Spectropolarimetry, Exp.Aston., 2010.

Charbonneau, D., Berta, Z.K., Irwin, J., et al., A Super–Earth Transiting a Nearby Low–Mass Star, Nature,2009, vol. 462, pp. 891–894.

Casertano, S., Lattanzi, M.G., Sozzetti, A., et al., Double–Blind Test Program for Astrometric Planet Detectionwith Gaia 2008, Astron. Astrophys., 2008, vol. 482,pp. 699–729.

Dvorak, R., Schneider, J., Lammer, H., and the CoRoTTeam, CoRoTs First Seven Planets: An Overview, Astro�phys. J., 2010.

Ekenbäck, A., Holmström, M., Wurz, P., et al., EnergeticNeutral Atoms around HD 209458b: Estimations ofMagnetospheric Properties, Astrophys. J., 2010,vol. 709, pp. 670–679.

Glassman, T., Newhart, L., Barber, G., Turnbull, M., andNOW Study Team, Planning an Efficient Search forExtra–Solar Terrestrial Planets: How to Find Exo–Earths with New World Observer, American Astron. Soc.(AAS), 2009.

Greiβmeier, J.�M., Zaraka, P., Spreeuw, H., et al., Predict�ing Radio Fluxes of Known Extrasolar Planets, Astron.Astrophys., 2007, vol. 475, pp. 359–368.

Holmström, M., Ekenbäck, A., Selsis, F., et al., EnergeticNeutral Atoms as the Explanation for the High–Veloc�ity Hydrogen around HD 209458b, Nature, 2008, vol.451, pp. 970–972.

Koechlin, L., Serre, D., Debra, P., et al., The Fresnel Inter�ferometric Imager, Exp. Astron., 2009, vol. 23, pp. 379–402.

Ksanformality, L.V., Transits of Extrasolar Planets, SolarSyst. Res., 2007, vol. 41, pp. 463–482.

Lammer, H., Kasting, J.F., Chassfière, E., et al., Atmo�spheric Escape and Evolution of Terrestrial Planets andSatellites, Space Sci. Rev., 2008, vol. 139, pp. 399–436.

Lammer, H., Bredehöft, J.H., and Coustenis, A., WhatMakes a Planet Habitable?, Astron. Astrophys., 2009,vol. 17, pp. 181–249.

Lammer, H., Odert, P., Leitzinger, M., et al., Determiningthe Mass Loss Limit for Close–in Exoplanets: WhatCan We Learn from Transit Observations?, Astron.Astrophys., 2009, vol. 506, pp. 399–410.

Léger, A., Rouan, D., Schneider, J., et al., TransitingExoplanets from the CoRoT Space Mission VIII.CoRoT–7b: The First Super–Earth with MeasuredRadius, Astron. Astrophys., 2009, vol. 506, pp. 287–302.

Lawson, P., Lay, O., Martin, S., et al., Terrestrial PlanetFinder Interferometer: 2007–2008 Progress and Plans,Proc. SPIE, 2008, vol. 7013, pp. 70132N–70132N–15

Lillie, C., TRW TPF Architecture. Phase 1 Study, Phase 2Final Report, 2001, Available from http://plan�etquest.jpl.nasa.gov/TPF/TPFrevue/Finl�Reps/Trw/TRW12Fnl.pdf

Perryman, M.A.C., de Boer, K.S., Gilmore, G., et al.,Composition, Formation and Evolution of the Galaxy,Astron. Astrophys., 2001, vol. 369, pp. 339–363.

Reiners, A., Bean, J.L., Huber, K.F., et al., Detecting Plan�ets around Very Low Mass Stars with the Radial Veloc�ity Method, Astrophys. J., 2010, vol. 710, no. 1.

Ribas, I., Guinan, E.F., Güdel, M., et al., Evolution of theSolar Activity over Time and Effects on Planetary

310


LAMMER et al.

Atmospheres. I. High–Energy (Irradiances (1–1700 Å),Astrophys. J., 2005, vol. 622, pp. 680–694.

Scalo, J., Kaltenegger, L., Segura, A.G., et al., M Stars asTargets for Terrestrial Exoplanet Searches and Biosig�nature Detection, Astrobiol., 2007, vol. 7, pp. 85–166.

Schneider, J., Boccaletti, A., Mawet, D., and the SEE–COAST Team, The Super Earth Explorer: A Corona�graphic Off–Axis Space Telescope, Exp. Astron., 2009,vol. 23, pp. 357–377.

Sozzetti, A., The Gaia Astrometric Survey EAS PublicationSeries, IAU Highlights Astron., 2010, vol. 15.

Sozzetti, A., Astrometric Methods and Instrumentation toIdentify and Characterize Extrasolar Planets: A Review,Publ. Astron. Soc. Pacif., 2005, vol. 117, pp. 1021–1048.

Stam, D., Spectropolarimetric Signatures of Earth–LikeExtrasolar Planets, Astron. Astrophys., 2008, vol. 482,pp. 989–1007.

Tavrov, A.V., Physical Foundations of Achromatic NullingInterferometry for Stellar Coronagraphy, J. Exp. Theor.Phys., 2008, vol. 107, pp. 942–951.

Vidal�Madjar, A., Lecavalier Des Etangs, A., Désert, J.�M.,et al., An Extended Upper Atmosphere around theExtrasolar Planet HD 209458b, Nature, 2003, vol. 422,pp. 143–146.

Watson, A.J., Donahue, T.M., Walker, J.C.G., et al., TheDynamics of a Rapidly Escaping Atmosphere: Applica�tions to the Evolution of Earth and Venus, Icarus, 1981,vol. 48, pp. 150–166.

Wood, B.E., Müller, H.�R., Zank, G., et al., MeasuredMass Loss Rates of Solar–Like Stars as a Function ofAge and Activity, Astrophys. J., 2002, vol. 574, pp. 412–425.

Wood, B.E., Müller, H.�R., Zank, G., et al., New Mass–Loss Measurements from Astrospheric Ly–α Absorp�tion, Astrophys. J., 2005, vol. 628, pp/ L143–L146.

1

2

3

4

4

SPELL: 1. Irradiances, 2. Mawet, 3. Spectropolarimetric, 4. Müller, 5. Ivanka

Documents

Exoplanet Status Report: Observation, Characterization and