Exo-Planets Press Kit

7/25/2019 Exo-Planets Press Kit

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1Explanets

Exoplanets

Press Kit


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Contents

Preface 3Early discveries 5Techniques fr detectin 7 Direct detectin 7 Imaging 7 Indirect detectin 7 Radial velcity tracking 8 Astrmetry 10 Pulsar timing 10 Transits 10 Gravitatinal micrlensing 11What can we learn frm explanets? 13What are explanets like? 14Life utside the Slar System 16Explanet research at ESo 17 ESos current explanet instruments 18 Explanet research in the future at ESo 19


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This guide prvides an verview f thehistry f explanets and f the currentstate f knwledge in this captivatingeld. It reveals the varius methds thatastrnmers use t nd new explanetsand the infrmatin that can be inferred.The last sectin summarises the impres-sive ndings f explanet research atESo and the current and near-futuretechnlgies available in the quest frnew wrlds.

Since planets were rst discvered ut-side the Slar System in 1992 (rbiting apulsar) and in 1995 (rbiting a nrmalstar), the study f planets rbiting therstars, knwn as explanets, r extraslarplanets, has becme ne f the mstdynamic research elds in astrnmy.our knwledge f explanets has grwnimmensely, frm ur understanding ftheir frmatin and evlutin t the devel-pment f different methds t detectthem.

Preface

Cver: Artists impres-sin f the explanetsHD 189733b | ESA,NASA, G. Tinetti (Uni-versity Cllege Lndn,UK & ESA) and M. Krn-messer (ESo)

Left: Artists impressinf an explanets rbitingits star | ESA, NASA, M.Krnmesser (ESo) andSTScI


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Left: ESo 3.6-m tele-scpe, La Silla observa-try | ESo

There are an innite number ofworlds, some like this world, others

unlike it.Epicurus letter t Herdtus(~ 300 BC)

A planet is an bject rbit ing a star that ismassive enugh bth t have achievedan almst spherical shape and t havecleared the rtating disc f dense gas,knwn as the prtplanetary disc, thatsurrunds a newly frmed star. Planetsdiffer in this frm dwarf planets (such asPlut), which d nt have enugh masst clear the prtplanetary disc area.

The rst detectin f an explanetccurred in 1992 when the astrphysi-cists Aleksander Wlszczan and Dale

Frail discvered three explanets. Theywere fund in an unexpected envirn-ment, rbiting the pulsar PSR1257+12.

In 1995, the Geneva-based astrnmersMichel Mayr and Didier Quelz de-tected the rst explanet arund a nr-mal (main sequence) star, 51 Pegasi.The planet, named 51 Pegasi b, hasarund half the mass f Jupiter and whiz-zes arund its parent star in just verfur Earth days, lying almst eight timesclser t it than Mercury is t the Sun.

Since 1995, this area f astrnmy hasbecme a very dynamic research eldand astrnmers have fund ver 450explanets (as f May 2010), using a hstf techniques.

Early discoveries


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Arti sts impressin fthe planetary systemarund HD 69830 | ESo


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Searching fr explanets is like lkingfr the prverbial needle in a haystack.Planets emit little r n light f their wn,while their hst stars shine brightly. See-ing the light frm a distant planet is likesptting a dim candle in frnt f a ragingfrest re.

Nwadays six investigative tls are usedt spt hidden explanets.

Direct detectin Imaging

Indirect detectin Radial velcity tracking Astrmetry Pulsar timing Transits Gravitatinal micrlensing

Direct detection

Imaging

The hardest way t detect an explanet ist try t image it directly. This is becausef the extreme cntrast between the lightemitted by the parent star and by thecmpanin planet. T expse the planet,the starlight must be dimmed r maskedin sme way s as t enable bservers tsee int the shadw. one methd is tuse infrared radiatin, rather than visiblelight. The visible light utput f a Jupiter-like planet is ne billinth f that f itshst star, while in the infrared the cn-trast is just a factr f a few thusandths.This is particularly true when the planet isstill very yung and thus cntracting,thereby emitting heat. Anther methd ist physically blck ut the starlight, usinga crngraph that masks the brightcentral cre f the star, leaving nly thecrna, the uter plasma regin f thestars atmsphere, visible and s allwingany nearby planets t shine thrugh.

Direct imaging is the nly way t assesssme imprtant physical parameters,such as the amunt f water n the sur-face and the prperties f any pssiblebisphere.

The adaptive ptics instrument, NACo,n ESos Very Large Telescpe (VLT) hasbtained the rst image f an explanet.The Eurpean Extremely Large Telescpe(E-ELT) planned fr 2018, will search frnew planets using direct imaging, thankst its very sharp visin.

Indirect detection

The majrity f all explanets discvereds far have been detected using indirectmethds identifying their existence bytheir effect n their hst star.

The presence f a planet affects its hststar in several ways. The weak gravity fthe planet pulls the star in a small circularrbit, intrducing a minute wbble thatcan be detected using radial velcitytracking r astrmetry (see pages 810).Alternatively, as the planet mves be-tween the star and the bserver, themeasured luminsity f the star willchange. These tiny variatins are impr-tant fr astrnmers, as it makes theindirect bservatin f explanets pssi-ble.

Techniques for detection

Beta Pictris as seen ininfrared light | ESo

Pssibly the rst imagef an explanet (redspt), btained withNACo at the VLT. Theplanet rbits a brwndwarf (blue spt in mid-dle) | ESo

debris disc

2003Planet Beta Pictris b

Beta Pictris

lcatin f the star

20090.5

Size f Saturns rbitarund the Sun


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The radial velcity methd has prven tbe the mst successful in nding newplanets. At present, the mst successfullw-mass explanets hunter is HARPS(High Accuracy Radial Velcity fr Plane-tary Searcher), which is munted nESos 3.6-metre telescpe at La Silla,Chile.

Radial velcity tracking

An astrnmer can determine muchabut a distant star by recrding itsspectrum. As the star mves in the smallrbit resulting frm the pull f the ex-planet, it will mve twards the Earth andthen away as it cmpletes an rbit. Thevelcity f the star alng the line f sightf an bserver n Earth is its radial velc-ity. Changes in the radial velcity f thestar cause the lines in the stars spectrumt shift twards redder wavelengthswhen the star is mving away frm us

and twards bluer wavelengths when theplanet is appraching us (see image).This is the Dppler effect, and i t is ntice-able with sund waves in everyday life,

fr example in the change f pitch f anambulance siren as it drives past n thestreet.

The peridic changes in the stars radialvelcity depend n the planets mass andthe inclinatin f its rbit t ur line fsight. These tiny changes r wbblescan be measured by a distant bserver.Astrnmers use high precisin spec-trgraphs t study Dppler-shifted spec-tra, lking fr small regular variatins inthe radial velcity f a star. As the inclina-tin f the planetary rbit is unknwn, the

measurement f this regular variatingives a minimum value fr the mass fthe planet.

The planetar y systemarund Gliese 581(artists impressin) |ESo


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The rad ial vel citymethd | ESo


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Magnification

10 Aug

2005

11 Aug

2005

Observer

Planet

Lens Star

Source star

Observer Source star

Time

Intensity

0.1

0.97

0.98

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1.01

0.1 0.05 0.050

Phase

Relative

Flux

OGLE-TR-132

OGLE-TR-1130.97

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Astrmetry

The astrmetry methd is similar t radialvelcity tracking and is used t detectexplanets by measuring the small regu-lar perturbatin in the psitin f a stardue t its unseen cmpanin. The starmves in a tiny circular rbit n the skywith a radius that depends n the massf the planet and its distance frm thestar, but nt n the inclinatin. N planetshave been discvered s far using thismethd.

Pulsar timing

The presence f a planet rbiting a staraffects the timing f the regular signalsemitted by the star itself. This phenme-nn can be used t detect planetsarund a pulsar. Pulsars emit radi wavesregularly as they rtate, creating a peri-dically pulsed beam, like a lighthuse. Ifan rbiting planet perturbs the mtinf the star, then the timing f the beam isals affected, and this is hw the rstexplanets were detected.

Transits

When a planet passes between the Earthand its hst star, this is knwn as a tran-sit. The planet blcks sme f the star-light during the transit and creates a peri-dic dip in the brightness f the star. Thiseffect can be measured using phtme-try, which measures the amunt f lightcming frm celestial bjects.

We can learn much abut the cmpsi-tin f a planets atmsphere frm plane-tary transits. As a planet passes in frnt

f its star, light frm the star will passthrugh the planets atmsphere, wheresme f it is selectively absrbed. Bycmparing the befre and after

1. The measured drp inbrightness f the starwhen the planet passesin frnt f it | ESo

2. Brightness variatins ftw stars with transitingexplanets | ESo

3. Light curve f oGLE-2005-BLG-390 | ESo

4. Gravitatinal lensingcaused by the pres-ence f a star and anexplanet | ESo


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Gravitatinal micrlensing

The gravitatinal pull f a large bject willbend the light frm distant bjects andamplify it, acting like a magnifying lens.When light frm the backgrund bjecttravels twards Earth, its path is bent rwarped as it bypasses any large fre-grund bject that is aligned with thebackgrund light surce. As the micrlens-ing effect wrks n radiatin frm thebackgrund surce, this technique can beused t study intervening bjects that emitlittle r n light, such as black hles, r

planets arund distant stars. Suppse thatthe aligned fregrund mass t be studied

is a star that is hsting a planet, then theamplied light curve frm the backgrundsurce will cntain an additinal side peak.The size and shape f the secndary peakwill depend n the mass and distance fthe planet frm the hst star (see theimage).

The explanet oGLE 2003-BLG-235/MoA 2003-BLG-53 was the rst planetdiscvered using this technique, in 2003.The disadvantage f the micrlensingtechnique is that the effect happens nlynce, as it relies n a unique chance

alignment f the fregrund and back-grund stars, and s measurementsmust be checked using ther methds.

spectral data f the starlight, the cmp-sitin f the planets atmsphere can bededuced.

The optical Gravitatinal Lensing Experi-ment (oGLE) lcated at Las Campanas,Chile, was used t nd the rst planetthrugh transit phtmetry (called oGLE-TR-56). Nwadays, sate llites in spacesuch as CoRoT and Kepler have fundnumerus transiting planets.

Radial velcity measurements, cmbinedwith transit phtmetry, make it pssible

t determine nt nly the mass f aplanet, but als its radius and density.

The Crab Nebula | ESo


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Planet-frming disc(artists impressin) |ESo

The central regin f theorin Nebula | ESo,M. McCaughrean et al.

Pssible rbitalmigratin f the plane-tary system arundHD 89830. Planets mayhave frmed far awayfrm the star and spi-ralled inwards ver time. |ESo


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Explanets are fascinating because theymay slve mysteries abut ur wn SlarSystem. There is a wealth f data availa-ble t study different types f galaxiesand stars, which has enabled astrn-mers t develp mdels and theries nstar and galaxy frmatin and t placeur wn galaxy and star amngst them.The Slar System is 4.6 billin years ld,but there is n way t measure directlyhw it frmed and it was, until recently,the nly planetary system that we knewf, s there was nthing t cmpare itwith. We had n idea if it was ne fmany, a typical example f a planetarysystem r a unique ne-ff. Studying thefrmatin f ther yung planetary sys-tems may give us answers.

Prtplanetary discs are regins f dustand gas rbiting very yung stars, whereplanets are frmed. Current theries fplanetary frmatin suggest that dustparticles start t cllapse under gravityand stick tgether, frming bigger andbigger grains. If yung prtplanetarydiscs survive the threat f stellar radiatinand impacts by cmets and meterites,then matter cntinues t clump tgetherand eventually planetids may frm. Plan-etids are celestial bjects bigger thanmeterites and cmets, but smaller thanplanets. After a few millin years, mst fthe circumstellar dust will have beenswept away as planetids accumulatemass and grw int planets.

Many f the planets fund s far arelarge, gaseus and very clse t theirstar, unlike the situatin in ur wn SlarSystem. The cncept f rbital migratinhas been revived t explain the clseprximity f sme giant planets t theirstar: these planets may have frmedundisturbed relatively far frm the starand then slwly spiralled inwards vertime.

What can we learn from exoplanets?


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Due t the limitatins in current detectinmethds, the majrity f planets discv-ered s far have been rather large Jupiter-sized r much larger. Althugh itis difcult t detect smaller planets, aplanet with less than twice the mass fthe Earth has been discvered.

There are smal l icy explanets as well asgigantic ht planets. one f the interest-ing questins t answer is hw the distri-butin f explanet type is linked t thetype f parent star. It is likely that thereare als explanets with rings and satel-lites, but these are difcult features tdetect.

What are exoplanets like?

0

Sun

Beta Pic b

2M1207

HR8799a,b,c

Frmalhaut b

GQ Lupi b

1RXS J160929.1-210524 b

20 40 10060 120 30080

Arti sts cncept fthe explanet rbitingFmalhaut | ESo(L. Calada), ESA, NASA

This diagram cmpares ur SlarSystem with sme f the variusplanetary systems imaged s far (the

Slar System is at the bttm f theimage, shwing the Sun alng withthe fur uter planets, Jupiter, Saturn,Uranus and Neptune)


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The current fcus f research int ex-planets is t develp the theries andunderstanding f planetary frmatin,and t understand hw the Slar Systemdevelped and what its future might be.Hwever, what makes explanets trulyfascinating fr mst is the pssibility fnding anther wrld that harburs life.

Exbilgy is cncerned with the studyf life utside f the Earth. The cnceptf life is subject t debate, but there isagreement in dening the features thatculd permit the develpment f carbn-

based life:

A planet shuld have a mass fbetween 1 and 10 terrestrial masses,be big enugh t hld its atmsphere,but nt s massive that it keeps tmuch hydrgen.

A planet must be in the habitable zne,smetimes called the Gldilcks Zne,which is dened as the band arund astar where water can be liquid. Thismeans that a planet can nei ther be tclse nr t far frm its star, as waterwuld be either gaseus r icy respec-tively.

Exbilgy is nt a fcus f currentexplanet research prjects, but is nefr the future. Future spectrscpic mis-sins ESAs Darwin and NASAs Ter-restrial Planet Finder missins areplanned fr launch ver the next decadeand will search fr xygen, carbn dix-ide and chlrphyll.

Life outside the Solar System

Arti sts impressin f anexplanetsarysystem | NASA, ESAand G. Bacn


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A list of ESOs most recent achieve-ments is given below.

2010: VLT detects rst superstrm n anexplanet. (es1026)

2010: Fr the rst time, astrnmers havebeen able t directly fllw themtin f an explanet as it mvest the ther side f its hst star.(es1024)

2010: Six explanets were fund rbitingin the ppsite directin t thertatin f their hst star chal-lenging theries f planet frma-tin. (es1016)

2010: With HARPS, astrnmers havediscvered the rst nrmal ex-planet that can be studied in greatdetail. (es1011)

2010: VLT captures rst direct spectrumf an explanet. (es1002)

2009: Astrnmers discver rst super-Earth with an atmsphere.(es0950)

2009: Sun-like stars that hst planetsappear t have destryed their lith-ium much mre efciently thanplanet-free stars. (es0942)

2009: HARPS discvers 32 new explan-ets, mstly lw-mass nes.(es0939)

2009: HARPS nds rst slid evidence fra rcky explanet. (es0933)

2009: Lightest explanet fund using themst successful lw-mass ex-planet hunter in the wrld, theHARPS spectrgraph.(es0915)

2008: First planet discvered arund afast-rtating ht star, discvered bythree undergraduate students andcnrmed by ESos VLT.(es0845)

2008: First direct image f a planet that isas clse t its hst star as Saturnis t the Sun. (es0842)

2008: Unsurpassed details revealed nthe mtin and makeup f planet-frming discs arund Sun-likestars. (es0827)

2008: A tri f super-Earths are bservedusing ESos HARPS instrument.Data suggests ne in three Sun-like stars have such planets.(es0819)

2007: Discvery that explanets may pl-lute the atmspheres f their par-ent stars with planetary debris.(es0729)

2007: ESo develps a new imagingspectrgraph s as t be able timage faint bjects bscured bytheir bright parent stars directly.This paves the way fr many thrill-ing new discveries. (es0728)

2007: Discvery f the mst Earth-likeplanet: lcated 20 light-years away,it may have water n its surface.(es0722)

2006: observatins shw that smebjects that are several times themass f Jupiter have a disc sur-runding them and may frm in asimilar way t stars. It thusbecmes much mre difcult tdene precisely what a planet is.(es0629)

2006: Detectin f three Neptune-likeplanets, each f a mass betweenten and twenty times that f Earth,arund a star that als pssessesan asterid belt. of all knwn sys-tems, this is the mst s imilar yet tur wn Slar System.(es0618)

2006: Discvery f the rst terrestrial-sized explanet, ve times the sizef the Earth.(es0603)

2005: Discvery f a planet with a masscmparable t Neptune arund alw-mass star, the mst cmmntype f star in ur galaxy.(es0539)

2004: Ingredients fr the frmatin frcky planets discvered in theinnermst regins f prtplane-tary discs arund three yungstars. This suggests that the fr-matin f Earth-like planets maynt be unusual.(es0435)

2004: First direct image taken f an ex-planet, paving the way fr mredirect studies. (es00428)

2004: Discvery f the rst pssiblercky explanet, an bject with 14times the mass f the Earth.(es0427)

2004: Cnrmatin f the existence f anew class f giant planet. Theseplanets are extremely clse t theirhst stars, rbiting them in lessthan tw Earth days, and aretherefre very ht and blated.(es0415)

2002: The discvery f a dusty, paquedisc surrunding a yung Sun-likestar, in which planets are frmingr will sn frm. This disc is simi-lar t the ne in which astrnmersthink the Slar System frmed.(es0214)

Exoplanet research at ESO

The VLT plat frm at

Paranal | ESo


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ESOs current exoplanet instruments

The grundbreaking discveries f recentyears were pssible thanks t the ESoinstruments searching fr fllwing: HARPS (High Accuracy Radial Velcity

fr Planetary Searcher) n the ESo 3.6-metre telescpe at La Silla fr radialvelcity high reslutin spectrscpy. Itcan measure velcities with a precisingreater than 1 m/s (r 3.6 km/h).

NACo n the VLT at Paranal anactive ptics and near-infrared imagerand spectrgraph that allws the sharpimaging f bjects smaller and fainterthan stars, such as explanets.

UVES n the VLT fr radial velcityhigh reslutin spectrscpy in the UVand visible.

EMMI n the NTT at La Silla spec-trgraph perating at visible wave-lengths.

FLAMES (Fibre Large Array Multi Ele-ment Spectrgraph), n ESos VLT atParanal fr multi-bre reslutinspectrscpy.

Swiss 1.2-metre Lenhard Euler Tele-scpe at La Silla high reslutinspectrscpy.

Danish 1.54-metre Telescpe atLa Silla lng-term mnitring.

AMBER studies f circumstellar envi-rnments and prtplanetary discs,imprtant fr planet frmatin studies.

VISIR studies f circumstellar envirn-ments and prtplanetary discs, impr-tant fr planet frmatin studies.

ISAAC (Infrared Spectrmeter AndArray Camera), attached t the VLT

MIDI, the MID-infrared Inter fermetricinstrument f the VLT Interfermeter.

The Atacama LargeMillimeter/submillimeter

Array | ALMA (ESo/NAoJ/NRAo)/L. Calada (ESo)


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Exoplanet research in the future at ESO

The PRIMA instrument f the ESo VeryLarge Telescpe Interfermeter (VLTI),which recently saw rst light at its newhme atp Cerr Paranal in Chile, willbst the capabilities f the VLTI t seesurces much fainter than any previusinterfermeters, and enable astrmetricprecisin unmatched by any ther exist-ing astrnmical facility. PRIMA will there-fre be a unique tl fr the detectin fexplanets.

The secnd generatin instrumentSPHERE fr ESos Very Large Telescpeis dedicated t the discvery and studyf new giant explanets rbiting nearbystars by direct imaging, in par ticular fplanets mre massive than Jupiter at var-ius stages f their evlutin, in the keyseparatin regime 1 t 100 AU (AU is themean EarthSun distance). SPHEREshuld have rst light arund 2011.

Mrever, tw future grund-based tele-scpes will be used t search fr ex-planets: E-ELT (Eurpean Extremely Large Tele-

scpe) expected t be able t imageexplanets directly, revealing their cm-psitin, and t detect, via the radialvelcity methd, Earth-mass planets.

ALMA (Atacama Large Millimeter/sub-millimeter Array) fr accurate astrm-etry measurements, pssibly even frdirect detectin. Detailed mapping fprtplanetary discs, which is impr-tant fr understanding planet frmatin.

The E-ELT | ESo


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