The Story so far

Big Bang Model – Three major pieces of evidence

- Problems – Horizon and Flatness problems

hence

Inflationary Big Bang – introduced by Guth (1981)

- solves these problems

History of Universe in terms of the Big Bang.

Finally – Formation of stars and galaxies.

Superforce reigns

GUTs

Electroweak era

QGP/Hadron phase transition

Universe becomes transparent

Voids on the largest Scale

The Evolution of Stars

Ideally we would follow a star’s “life” from its genesis in a cloud of gas and dust to its “death”.

However the timescale is way beyond our life span.

The alternative approach is to realise that the numbers of stars we can see is very large. We assume that a) the lifetimes of stars are shorter than the age of the Universe and b) we can observe stars atall stages of development.

We have seen now how to measure stellar distances, masses, surfacetemperatures, luminosities etc. We can now ask whether these quantities are correlated in any way.

One way to look at this is the Hertzsprung-Russel diagram.

Hertzsprung-Russell Diagram

1.The H-R diagram plots Luminosity against Surface Temperature. Note:-Log Luminosity is used because of the large range and it is plotted against decreasing temperature.2.Each star is represented by a point on the diagram.3.The results depend to some extent on the sample of stars.They could be from stars within a limited volume round the Solar system, members of a cluster,stars of apparent brightness above a certain limit,etc.4.Any H-R diagram shows that only a limited combination of values of T and L are allowed.5.Most stars lie on a thin strip running diagonally across the diagram This is the Main Sequence.6.Top right is also populated with brighter stars with lower T.Red Giants7.Lower left is also rich in stars.They are bluish-white and small.The size is comparable to that of the Earth but with approx. the same mass as the Sun. They are White Dwarfs.

Hertzsprung-Russell Diagram

1. By restricting the range of stars plottedone can test ideas of stellar evolution.Here we see stars from a particular globular cluster.These groups of stars are very old anddifferent from open clusters. The ages are such that only stars of 1 solar massor less are left.They are close to the ageof the Universe. Most other stars not on the main Sequence here are Whitedwarfs or brown/black dwarfs.Ingeneral they are Population 2 stars withless than 1% of heavy elements compared with Population 1 stars where it is 2% or so.

Temperature [Contrast with stars in the disc.]

M31-Andromeda Galaxy-2.2Mly from Earth, Part of our Localcluster of galaxies.

Stellar Birth1.Seeing the early stages is difficult. It starts with a collapsing cloud of gas and dust and it is not hot enough to shine so we don’t see it. As it collapses half of the potential energy is turned into kinetic energy [Heat]. [Virial Theorem] Triggering of such collapses is not fully understood.

2.If the temperature of the gas cloud reaches high enough temperature the particles[protons]will have enough energy to interact and nuclear reactions will begin at about 8 million Kelvin .As we will see this releases energy which heats the gas and raises its pressure.

3.If heated enough, the gas pressure will countermand the gravitational contraction and the star will stabilise under these two opposing forces.

4.At this stage the star will be moving to the left on the H-R diagram and will end up on the Main Sequence.

The proton-proton chain

1H + 1H = 2H + e+ +1H + 1H = 2H + e+ +1H + 1H = 2H + e+ +

1H + 1H = 2H + e+ + (B)1H + 2H = 3He + (C)

1H + 1H = 2H + e+ + (A)

1H + 2H = 3He + (D) 3He + 3He = 4He + 1H + 1H + (E)

Thus the sequence of reactions turns 4 protons into an alpha particle.

1H + 1H + 1H + 1H 4He + 2e+ + 2e + 3

Since the alpha particle is particularly tightly bound this process ofturning 4 protons into an alpha releases about 26MeV of energy.It is this energy which heats the stellar interior,allows it to withstandthe gravitational pressure and causes it to shine!

The p-p chain;the reactions which power the Sun

Overall - 4p 4He + 2e- +2 + 26.7 MeV

The CNO-Cycle: In stars where we already haveC,N and O we can get hydrogenburning 4p + 2e- + 2 +26.4 MeV

The C,N and O nuclei act ascatalysts for the burning process

Hans Bethe-1938

Life Cycle of Stars and Nucleosynthesis

1. Formation from large clouds of gas and dust.

2. Centre of cloud is heated as it collapses under gravity

3. When it reaches high enough temperature then nuclear reactions can start. 4p 4He + 2e + 2ν + 26.7 MeV

4. This raises temperature further and star eventually reaches equilibrium under heating internally and gravitational collapse.

5. The process of making heavier nuclei occurs in the next stage.

Zero Age Main Sequence – Temperatures and magnitudes at which differentmass stars first reach equilibrium.

After the Main Sequence

1.Once a star’s hydrogen is used up its future life is dictated by its mass.

2.During the H-Burning phase the star has been creating He in the core by turning 4 protons into a He nucleus plus electrons and neutrinos. Once the H burning stops in the centre the star contracts and some of the potential energy is turned into heat. If the core temperature rises far enough then He-burning can begin. Coulomb(electrostatic) barrier is 4 times higher for two He nuclei compared with protons.

3.Now we face again the problem of there being no stable A = 5 or 8 nuclei.

4.It turns out that we can bypass these bottlenecks but it depends critically on the properties of the properties of individual levels in Be and C nuclei.

The Creation of 12C and 16O• H and 4He were made in the Big Bang.Heavier nuclei were not produced because there are no stable A = 5 or 8 nuclei. There are no chains of light nuclei to hurdle the gaps.• How then can we make 12C and 16O?• Firstly 8Be from the fusion of two alphas lives for 2.6 x 10-16 s cf. scattering time 3 x 10-21 s. They stick together for a significant time.• At equilibrium we get a concentration of 1 in 109 for 8Be atoms in 4He. • Salpeter pointed out that this meant that C must be produced in a two step process.

• Hoyle showed that the second step must be resonant.He predicted that since Be and C both have 0+ s-wave fusion must lead to a 0+ state in 12C close to the Gamow peak at 3 x 108K.• Experiment shows such a state at 7654 keV with = 5 x 10-17s

The 7654 keV statehas / 1000

A rare set of circumstances indeed!

1010 years

The Earthwill be

engulfed!!

++ 12C + 16O

Red Giant(3000ºK

Red)

H burning

Path of Solar Mass Star on Hertzsprung Russell Diagram

White Dwarf

H, N, O¡¡only!!

(Hubble)Fluorescence

Helix Planetary Nebula in the constellation of Aquarius

Binding Energy per nucleon as a function of Nuclear Mass(A)

The End of Fusion Reactions in Stars

A = 56

•When two nuclei fuse together energy is released up to mass A = 56 Beyond A = 56 energy is required to make two nuclei fuse.•As a result we get the burning of successively more massive nuclei in stars.First H, then He, then C,N,O etc.•In massive stars we eventually end up with different materials burning in layers with the heaviest nuclei burning in the centre where the temperature is highest.•When the heaviest(A = 56) fuel runs out the star explodes-Supernova

[Remember E = mc2]

Gravitación

Etoile massive supergéante

C. THIBAULT (CSNSM)

H He

C O

Ne Na Mg

Al Si P S

Fe

If the star is eight times more massive than the Sun

Strong Force

SUPERNOVA

Death of a Red Giant:SUPERNOVA

October 1987 1056 Joules of energy

This happened 170000 years ago in the nearest galaxy

The Destiny of the Stars…

C. THIBAULT (CSNSM)

MainSequence

Red Giant

White Dwarf

Massive StarsSupernova

Density/

AÑOSAlgún

segundo

BrownDwarf

109

109

109

100 kg

Spectrum of Cassiopeia

We see here the remnants of asupernova in Cassiopeia.Thisradio telescope picture is takenwith theVery Large Array in New Mexico.From the measured rate of expansion it is thought to haveoccurred about 320 years ago.It is 10,000 ly away. With optical telescopes almost nothing is seen.

The inset at the bottom shows a small partof the gamma ray spectrum with a clear peak at 1157 keV,the energy of a gamma ray in the decay of 44Ti.

Full-sky Comptel map of 1.8 MeV gammas in 26Mg following 26Al GS -decay.

(a) Spin traps, eg. 26Al, (N=Z=13) 0+ state -decaying spin-trap.

5+, T=0 0 keV, T1/2=7.4x105 yrs

0+, T=1 228.3 keV, T1/2=6.3 secs(decays direct to 26Mg GS via superallowed Fermi+…forking in rp-process

(decays to 2+ states in 26Mgvia forbidden, l=3 decays).

e.g., Diehl et al., Astron. Astrophys 97, 181 (1993); Publications of the Astr. Society of the Pacific 110:637 (1999)

Principe de la nucléosynthèse

C. THIBAULT (CSNSM)

616058

59

59

5756 5855

protons

26 Fe 54

27 Co

28 Ni

29 Cu

62

63 65

•• Capture d’un neutron •• Radioactivité –

epn

neutrons30 4035

64

Il y a compétition entre

Principle of Nucleosynthesis

Capture of a neutron

Competition between two processes

Radioactivity

Part of the Slow Neutron Capture Pathway

In Red Giant Stars neutrons are produced in the 13C( 4He,n) 16O or22Ne(4He,n)25Mg reactions.The flux is relatively low.As a result there is time for beta decay before a second neutron is captured.The boxes here indicate a stable nuclear species with a particular Z & N.Successive neutron captures increase N. This stops when the nucleus created is unstable and beta decays before capture.

The pathways for the s- and r-processes

S-process:Neutron flux is low so beta decay occurs before a second neutron is captured.We slowly zigzag up in mass.

R-process:Neutron flux is enormous and many neutrons are captured before we get beta decays back to stability.

The Abundances of the Elements for A = 70 - 210

Note the double peaks atN = 46/50, 76/82, 116/126

They are due to productionby the two separate processes

S – process &R-process.

M74 Gemini

M31-Andromeda Galaxy-2.2Mly from Earth, Part of our Localcluster of galaxies.

The Solar System

The Solar System

The formation of the Solar System has been a topic of great interest for a long time.

As yet there is no definitive theory but there is an emerging consensus.

There have been (are) theories that start with a) A comet colliding with the Sun and knocking the material that composes the planets out of it, b) A close encounter with another large body, with the resulting tidal effects causing part of the Sun’s material to be ripped out.

These theories face a variety of problems such as the differences in composition between the Sun and the planets.

Other theories rely on the accretion of material from interstellar space. This solves the difference in composition from the Sun but not between planets.

The basis of the models that are popular now is the idea that Sun and planets all formed from the same material. Differences in composition arise during the formation of the system. [Does not preclude a mixture of these ideas]

Many problems remain but now there seems to be convergence on a theory of this kind.

The Solar System

Before looking at the theories we should remind ourselves of some of the facts.

The Solar System consists of a very large number of objects, held together by gravity and obeying Kepler’s Laws.

The picture is not to scale. Itshows the Sun with the four, innerTerrestrial planets, followed furtherout by the Asteroid belt then theGas giants.

Then we have comets , a large number of moons etc.

The Solar System

Sun - a Main Sequence Star of mass 2 x 1030 kg

- radius = 696,000 km

- Luminosity = 3.86 x 1026 W

- Distance to centre of galaxy = 8000pc = 26,000ly

- density = 1410 kg/m3

Nine planets

137 known moons

Asteroids

Comets

Gas and dust

The Solar System

We again see the solar system below but this time withoutthe Sun. On the right we see the scales of the orbitsof the various planets.

Dis

tanc

e-10

9 m

Kepler’s Laws

1.The planets orbit the Sun in ellipses with the Sun at one focus.

2.The line joining the Sun and a planet sweeps out equal areas in equal times.

3.The square of the period of a planet is proportional to the cube of the semi-major axis of the ellipse.

P2 a3

Note:- Elliptical orbits were an essential innovation but for simple calculations one can assume that the orbits are circles. In general it is a good approximation.

Convenient Measure of distance -Astronomical Unit(1 au) = Average Earth-Sun distance = 1.496 x 1013 cm = 1.496 x 1011 m

Plot of a3 versus P2 for the planets in the Solar system

- Here a is in AU and P is in Earth Years.

Reminder:All three of Kepler’s Laws are rigorously obeyed wherever two objects move under their mutual gravitationalattraction.

Kepler’s Third Law

P2

a3

Clearly P2 a3

Asteroids

Asteroids lie in belt from 2-3.5AU from Sun.

Planetary Orbits

Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

Semi-major axis (106 km)

Sidereal Period

Orbital Eccent.

Direction of revn

Angle to plane to ecliptic(degs.)Angle of Plane to spin axis(degs)

Rotation Period (Days)

Surface Temp.

Mass(1024 kgm)

57.9 108.2 149.6 227.9 778.4 1424 2871 4499 5906

0.241 0.615 1.0 1.88 11.9 29.5 84.0 165 248

0.21 0.01 0.02 009 0.05 0.06 0.05 0.01 0.25

7.0 3.4 0 1.8 1.3 2.5 0.8 1.8 17.1

0.1 178 23.5 25.2 3.1 26.7 97.9 29.6 122

58.7 243 1.0 1.03 0.41 0.43 0.72 0.67 6.4

100-620 730 300 220 130 97 58 58 50

0.33 4.87 5.98 0.64 1900 569 86.8 102 0.013

They are all the same apart from Venus

Formation of Solar System

Key piece of evidence:- Sun and planets orbit in same direction and lie almost in the same plane.

This suggests Sun and planets all formed at the same time from a mass of gas and dust, which was rotating.

Why did this mass come together?

What triggered this process?

Here there is no clear answer – Perhaps a shock wave from a supernovaor some other event.

Basic Idea of Nebular Hypothesis

Here is the idea with which we are already familiar.The system forms from a collapsing cloud of gas and dust

If the whole cloud is spinning slowly whenthe collapse starts then it will speed upas it gets smaller in order to conserve angular momentum.

Formation of Solar System

The initial cloud or nebula must have had a small rate of rotation. As the cloud collapses it would speed up to conserve angular momentum. Two results:- the rotation we see today and the formation of a disc with the planets forming in the outer part of the disc as the material clumps together.

Protoplanetary disc or Proplyd

Solar System – Role of Condensation Temperature

Temperature would play a large role in determining the composition of the planets.

For the inner planets T is high so molecules have higher average velocities and light gases escape from the gravitational field.

Metals condense out at higher T so the inner planets have more metals or heavyElements.

For outer planets T is lower and masses higher so they retain the light gases.

The angular momentum leads to a flattened disc which explains why all the planetsare in the same plane. T rose in centre and stayed at say 50K in the outer reaches.Rocky material stayed solid near the protosun and gases and other icy substances

vaporised. The planetesimals of rock coagulated to form inner planets. The icygrains on outside grew together and then accumulated gases.

Note:- Chemical differentiation vs. heterogeneous accretionFormer - material accumulated and radioactive decay caused melting and Fe-rich

Minerals sank to centre.Latter- Fe and Fe oxides were first to condense so cores formed early. Later Si-rich

Material condensed on top.

Formation of Solar System

Here is another view of the same process. Initially T = 50K so solar nebula would have been filled with dust grains, small ice particles etc plus H and He as gases. As protosunformed it heated central part leaving outer parts at 50K. In inner section everything except materials with high condensation temperatures were vaporised i.e.Fe,Si,MgS,Al,Ca and Ni and their oxides remained.Protoplanets formed from planetesimals by accretion, which collided to form planets.

Solar System

Question of angular momentum. Most of the angular momentum is in the disc-the ang.mom. of the planets. The Sun has only 0.5% of the total. Why?

Rotating solar nebula was gaseous and hot. The molecules move quickly and are ionised in collisions – thus a plasma of ions and free electrons forms. The motion of charged particles creates a magnetic field. The nucleus of the solar nebula thus had a magnetic field associated with it. Matter close to the nucleus was also partially ionised and moved with it.

T for disc fell as we moved away from the nucleus so that more and more electrically neutral molecules would have been found as we moved out from the centre. As the charged particles were dragged round they collided with uncharged particles and so they dragged the uncharged particles with them and transferred ang.mom. to the disc.

A particle whose ang.mom. thus increased would move out from the centre.so that total ang.mom. is conserved. Nucleus continued to contract and increase its rotational velocity(although at a slower rate due to the ang.mom. transfer) while the matter moving away slowed as its orbital radius increased. In principle all of the ang. Mom. could be transferred to disc.

Eagle Nebula – Star Formation

About 1 light year Enlargement of regions where young starsare forming. Tips are about size of theSolar system.

Hubble space telescope pictures of star-forming region in the Eagle Nebula.

Origin of the Solar System

A small part of the ORION nebulaIn which young stars are beingformed from small pieces of the giant interstellar cloud.Our solar system presumably formed as a small part of a gas Cloud collapsed under gravity. This piece of collapsed cloud we call the solar nebula.

Before the collapse began it would have been spread out over a few Light years in diameter. It was cold and had a low density. Why did it start to collapse?Perhaps it was the result of a shock wave from an exploding star.

Protoplanetary discs forming in the ORION Nebula. Insets show examples. They areIn false colour and the picture is a mosaic of HST pictures. A young star is at centreof each proplyd.

Size of Solar system

Jovian Planets

Outer planets probably began in same way with accretion of planetesimals. Since Twas low this included ice particles. Gas was moving slowly so it got attracted by gravitational force. Process stopped when gas ran out.Result - a small solid core with a large gas envelope.

This is thought to be origin of four Jovian planets.

Initially they would have been hotter and would have behaved like a miniature solar System and we can imagine their satellites forming like the planets in the solar system.

Solar wind plus accretion would have scavenged all of the gas and dust and planets would then have stabilised at present sizes.

Extra-Solar Planets

Are there other “solar systems”? The unequivocal answer is YES. We now have evidence of at least 100 planets around other stars.

There is a systematic search for such objects. For example at the 3.9m Anglo-Australian telescope.

Star

Planetplanet

As the planet orbits the star it will cause it to “wobble” back and forth in space. This will also cause the light from the star to be Doppler shifted. The AAT team can detecta Doppler shift to an accuracy of 3m/sec. This is the basis of their planet-hunting technique.

The latest such planet was observed around a star called Tau Gruis and is of the size of Jupiter. It is about 100ly away. It is three times further from its star than Earth is from the Sun.

Extra-Solar planets

Star PlanetVariety of methods used to look for them.

- radial velocity measurement

- astrometry – looking for slight variation in position

- Imaging – looking for reflection of light from planet

- Photometry (occultations)

So far we have only been able to detect the effects of Jovian-like planets.

Earth-like planets are too small to detect by these methods.

SummaryExtrasolar planets known within 200 pc of Earth.

This picture shows their distances from the stars they orbit in AU

Formation of Binary Star Systems

A large fraction of all stars are binary systems.

They are important for astronomers because they allow us to measure masses.

The collapsing nebula idea gives a natural explanation.

The Sun

Sun - a Main Sequence Star of mass 2 x 1030 kg

- radius = 696,000 km

- Luminosity = 3.86 x 1026 W

- Distance to centre of galaxy = 8000pc = 26,000ly

- density = 1410 kg/m3

Aside:- Source of energy. Typical chemical reaction-1eV = 1.6 x 10-19 Joules

No.of atoms needed to provide Sun’s luminosity = 3.9 x 1026 / 10-19

= 3.9 x 1045 atoms

Length of time to consume all of Sun = 1057 / 3.9 x 1045 = 3 x 1011 s = 10,000 Years!!!

Surface of the Sun

Photosphere = layer at which photons finally escape from the surface. Average T is 5850K but close up we see it is granulated. This is the result of convection. The bright areas are where hot gas bubbles upwards and the dark edges are where cool gas descends. It is like the surface of water boiling in a pan.

Sunspots and Solar Surface

One of the most striking features of the solar surface-sunspots. T is ~ 4000K, rathercooler than normal surface temp of 5850K. Why is the region not heated? It turns out

that these are regions with strong magnetic fields and the fields cause charged particles to spiral along magnetic field lines. No easy motion at rt. angles to field lines.

Solar Prominences. Fields from two sunspots often go high above the photosphere. These loops of

Magnetic field sometimes appear as solar prominences in which the field traps gas that can glow for days or even weeks. They can rise to 100,000 kms above the surface

Solar flares are even more dramatic – they usually occur

in vicinity of sunspots Suggesting they may be due toa collapse in the magnetic fieldwith a large release of energy.

This heats the plasma andaccelerates the charged particles

to high velocity.

Solar Prominence

UV photo of this veryLarge solar prominence.It is 20 times Earth size.

Courtesy of A..King

Courtesy of A.King

Mercury

Mass = 3.3 x 1023 kgDistance from Sun = 0.307 – 0.467 AUOrbital period = 87.97 daysRotational Period = 58.6 daysDensity = 5430 kg/m3

Average surface Temp. = 350 – (-170) degrees centigrade

Decent photographs only from Mariner 10 spacecraft in 1974

Surface looks like the moon. With the results of many impacts clearly visible.It has a large iron core and a magnetic field.

Mercury is not in synchronous rotation round the Sun. It makesthree rotations on its axis for every twice it orbits the Sun. This is related to the large eccentricity in its orbit.

Venus

Distance from Sun = 0.723 AUMass = 4.869 x 1024 kgOrbital Period = 224.7 daysRotational period = 243 daysDensity = 5243 kg/m3

Surface temp = 733KSurface Pressure = 90 atmospheres

Covered by a thick, unbroken layer of clouds.It rotates in retrogade rotationClouds are transparent to radiowaves andmicrowaves.Large number of space probes aimed at VenusStrong greenhouse effect so surface is hot.

RussianVenera-14Satellite landedAnd we seesurface

Venus-Second Planet out

Terrestrial Type planet. Covered in thick cloud of ammonia etc. Surface is rockyAs we can see on the radar maps. Density similar to Earth.

Volcanic activity is probably responsible forInjecting substantial amounts of sulphuricAcid and sulphur dioxide in atmosphere of Venus.

Lava flows clearly visible via radar

Lots of volcanic activity

No evidence of plate tectonics.

Earth

Mass = 5.97 x 1024 kgDistance to Sun = 1.496 x 108 kmDensity = 5515 kg/m3

Surface Temperature = 333KOrbital period = 365.256 daysRotational period = 23.9345 hours.

Troposphere-heated only indirectly by Sun.Stratosphere – Lot of ozone so it absorbs UV heavily. T increases with height.Mesosphere – Little ozone so UV is not absorbed. T decreases with height.

No defining edge to atmosphere.

Earth Observed from Space

Earth seen from Apollo 11

Galileo shot of Earth and its Moon

Galileo shot of South America

Structure formed in Differentiation process.Structure formed in Differentiation process.

After approx 109 years Earth melted due to a) gravitational energy. from formation, b) Meteor bombardment and c) radioactive decay.

Whilst molten, gravity concentrated denser material near the centre. When it solidifiedagain apart from outer liquid core it had a layered structure.

As the outer layers cooled large cracks developed in the lithosphere because of thermalStress-this leads to favourable conditions for plate tectonics.

Earth

We can study Earth’s interior with seismic waves.

P-waves:-Longitudinal waves which propagate in liquids and solids.S-Waves:-transverse waves propagate in solids but not liquids

Seismic studies plus “theory” suggest the structure on the left. Solid inner core (Fe + Ni), Liquid outer core(Fe+Ni).Diameter 7000km.Crust = tens of km.Mantle = region between core and crust.Lithosphere = crust + upper part of mantle.Aesthenospshere = region of plasticity

Plate tectonics.

Crust is thin (tens of km). Lithosphere is broken into large plates. AesthenosphereIs plastic and kept so by heating from radioactive decay.. Very slow convection thenprovides horizontal force on plates to make them move.

Seismic activity

laser ranging can detect few cms. per century.

fossil record supports theory.

Future:Australia will join Asia. Parts of California will “leave” USA.Africa will separate from Middle East. Italian boot will disappear.

Earth’s Atmosphere

Sunlight warms surface which heats lower part of troposphere. Resulting verticalT variation causes convection currents which lead to the large variation in the weather.

The atmosphere is also strongly affected by the Earth’s rotation, namely by the CoriolisEffect.

Oxygen all came from plants. H and He gone at an early stage

Coriolis Effects

Solar Heating and Coriolis Forces

Winds are driven by solar heating. This would suggest N-S pattern of air flow.Coriolis forces deflect air to the right in N.hemisphere and to left in S.hemisphere.

In other words you might expect a natural air flow of hot air from the equator towards the poles.However the Coriolis effect deflects the air molecules. We end up with a very general pattern as shown.

Earth’s Magnetic Field

It is like a simple bar magnet.Axis is tilted relative to rotation axisRemember Magnetic field is the result of electrical currents.

Van Allen belts

Field is thought to be due to electrical currents in the spinning liquid outer core.This Is called the dynamo effect. Rocks formed from molten state retain theirmagnetism from that time. Accordingly fossil records show field has reversed every million years or so.

Charged particles spiral along the field lines and are reflected at Mirror points.

Primary source of these particlesis the solar wind.

They are responsible for Aurora.

Earth’s Magnetosphere

Solar wind = stream of ionised gas from Sun. velocity = approx 400 km/secondIt varies in intensity depending on solar activity.When it encounters Earth’s field it is deflected.Region behind the Bow Shock is called the Magnetosphere. It largely preventsthe solar wind entering. Leakage causes Van Allen belts, Aurora etc.

Aurora over Circle, Alaska

Delicate colours are due to collisions between energetic electrons and O and N molecules in the atmosphere.

Aurora in UV in Northern hemisphere from Nasa’s Polar satellite.

U.S.A. at night from space.

Mount Etna from space

Earth Observation

Earth Observation can be at any wavelength. Here it is in Infra-red and we see the distribution of water vapour.

The Moon

Mass = 1/80 x Earth’s massMean distance = 384,000 kmDiameter = ¼ x Earth’s diameter.Orbit eccentricity is approx 0.05Daytime T = 373 KNightime T = -160K No atmosphere to store heat.Density = 3.4 g/cc

Apollo rock samples show material is as old as Solarsystem. They are older than Earth rocks because of Volcanic activity here.

Structure of Interior

Largely dead geologically

No magnetic field in essenceMaybe in past it was bigger.Any seismic activity due to tidal effects.

Craters from meteor impact

Early molten stageVulcanism ended some 3 billion years ago

How did Moon form?

1.Fission Theory:-Once part of Earth and separated in some way-Pacific basin is favourite site for this.

2.The Moon formed somewhere else and was captured by Earth’s field.

3.Condensation theory:- Moon and Earth condensed together.

4.Colliding planetesimal theory:- Moon condensed from debris.

5.Ejected ring theory:- Large Planetesimal struck Earth and ejected material that formed Moon.

First three are essentially ruled out because of differences in the Material on Moon and Earth.

Fifth is the currently favoured theory.

Mars from Viking 2

Mars-Fourth Planet Out

Mass = 6.418 x 1023 kg

Distance from Sun = 1.381 – 1.666 AU

Orbital Period = 686.98 days

Rotational Period = 24 hours 37 min.

Diameter = 6794 km.

Average density = 3934 kg/m3

Surface Temperature = 133-293K

Mars-Fourth Planet Out

Prominent features on surface - Meteor craters - Huge volcanic cones

Gorges larger than Grand canyon

Vast sedimentary deposits

Valleys that look as if they were formed in water flow

No plate tectonics.

Note:- craters are thought to have been formed at a very early stage as in the caseof the Moon. This process stopped when all the debris in the solar system had been Mopped up.

Frozen carbon dioxide at Pole

Valles Marineris 500 m wide and up to 6 km deep.

Variation in temperature at site of Viking 1

Surface Atmospheric pressure = 1/200 atmosp. pressure on Earth

Atmosphere = 95% CO2 plus 5% N

Large Dust Clouds due to seasonal heating

Jupiter

Mass = 1.899 x 1027 kgDistance from Sun = 4.95 – 5.455 AUOrbital period = 11.86 yearsRotational period = 9 hours 50 minsDiameter = 133.7 – 142.98 x 106 mAverage density = 1326 kg/m3

Average Temperature = 165K at cloud tops.

Largest object in solar system

Large number of Moons

Great Red spot is strong feature of surface

Weather patterns are due to solar and internal heating and differential rotation.

Shape is oblate (6.5%). This due to rotation of core.

Jupiter-The largest Gas GiantJupiter has a volume approx 1000 times the Earth’s volume..The mass = 1.9 x 1027 kgmDiameter is 142,800 kms.

It has a very dynamic weather system-atmospheric clouds,storms and latitudinal bands.

The Great Red Spot

The Great Red Spot is a complex storm moving in a counter-clockwise direction. At the outer edge material appears to rotate in 4-6 days. Near the centre motions are small and random.

Atmosphere is very deep, maybe including thewhole planet. It is very like the Sun. It is composed mainly of H and He with small amounts of Methane, ammonia, water vapourand other compounds.At great depths the pressure is very high and atoms are broken up. In this state H becomesa metal.

The four Galilean Satellites

They all orbit more or less in planeof planet’s orbit. Their motions are closely linked. The tidal effects arevery strong.They all rotate in same direction as orbit.Large number of other satellites.

Although all of “publicity” is for Saturn’srings we see here that there are rings for Jupiter.

Jupiter

Jupiter has 28 known satellites, four of which were observed as long ago as 1610.They are Callisto, Europa, Ganymede and Io. There is also a faint ring system.The image below is a collage of images acquired by Voyager and Galileo spacecraft.We see the Valhalla region of Callisto in the lower right. Inside the four GalileanMoons are Amalthea(top), Metis and Adrastea(to right) and Thebe(left).

Jupiter’s rings and moons exist within an intense radiation beltof ions and electrons trapped in theplanet’s magnetic field.

This field stretches out 3-7 Mkms towards the Sun and 750 Mkms towards Saturn.

Saturn-Another gas Giant

Saturn’s rings are complex

Pluto and Charon

Comets

Nucleus = mixture of ice and dust.Ion tail = Ions from comet are swept directly away from comet by solar wind.Dust tail = photons hitting dust particles are absorbed and hence exert a pressure on dust.Tails always point away from Sun.

Comet Hale-Bopp photographed over Boulder Colorado (1997)

Asteroids

Approx 105 asteroids spreadOver 1017 square km.

Largest is CERES with diameter Of 934 km. It accounts for 1/3 of totalAsteroid mass.

Probably planet did not form because of huge pull of Jupiter.

They occasionally collide with each otherand with Earth

Photograph of EROS asteroid from NEAR spacecraft. It is about 40 kms in length.Appearance is probably typical of most asteroids. Note its non-spherical shape, alsotypical of such small objects.

Solar System

Schematic view of the solar System.

The insets show a COMET and an ASTEROID

Note the asteroid belt betweenMars and Jupiter

Further out we have the Kuiper belt and much furtheraway the Oort Cloud.

End

Solar System Montage

Saturn-Another Gas Giant

Solar System

The planets of the Solar system are classified as Terrestrial or Jovian.

The four inner, terrestrial planets are close to the Sun. They are quite warm- Noon on Mercury = 600K and on Mars = 300K

At top of clouds on Jupiter = 150K cf 63K on Neptune.

Inner planets – densities 5.4-3.9 gcm-3 . Masses typically 1024kg Outer planets- 0.7-2.0 1026kg

Conclusion-terrestrial planets contain a large amount of material denser than rock. Whilst outer planets probably have solid cores of Earth dimensions but with extensive gaseous atmospheres.

All the planets except Mercury and Venus have satellites. At least 50 are known. Seven are comparable in size to Mercury – Moon, Io, Europa, Ganymede, Callisto, Titan, and Triton

Artist’s Impression

This how the possible scene from a moon around the recentlyDiscovered planet. The star is 6th

magnitude and takes 4 years to Orbit at a distance three times the Earth-Sun distance.

There is,of course, no evidence of a moon.

So far we only see planets ofJupiter-like mass but they fall intotwo groups-those very close in and those a long way out.

So far we have no explanation of this.

10-15 m

107 m1012 m

1019 m

1022 m

10-9 m

10-6 m10-5 m

10-10 m

10-14 m

Telescopes

Microscopes