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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 at all stages of development. We have seen now how to measure stellar distances, masses, surface temperatures, 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 Giants 7.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. Temperature By restricting the range of stars plotted one can test ideas of stellar evolution. Here we see stars from a particular globular cluster. These groups of stars are very old and different from open clusters. The ages are such that only stars of 1 solar mass or less are left.They are close to the age of the Universe. Most other stars not on the main Sequence here are White dwarfs or brown/black dwarfs.In general they are Population 2 stars with less than 1% of heavy elements compared with Population 1 stars where it is 2% or so. [Contrast with stars in the disc.] M31-Andromeda Galaxy-2.2Mly from Earth, Part of our Local cluster of galaxies. Stellar Birth 1.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+ + (A) 1H + 1H = 2H + e+ + 1H + 2H = 3He + (B) (C) + 2H = 3He + 3He + 3He = 4He + 1H + 1H + (D) (E) 1H 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 of turning 4 protons into an alpha releases about 26MeV of energy. It is this energy which heats the stellar interior,allows it to withstand the 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 have C,N and O we can get hydrogen burning 4p + 2e- + 2 +26.4 MeV The C,N and O nuclei act as catalysts 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 different mass 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 state has / 1000 A rare set of circumstances indeed! 1010 years Red Giant (3000ºK Red) H burning The Earth will be engulfed!! ++ 12C + 16O 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 The End of Fusion Reactions in Stars A = 56 Binding Energy per nucleon as a function of Nuclear Mass(A) [Remember E = mc2] •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 If Etoile the star is massive eight times more massive than the Sun supergéante H He C O Ne Na Mg Al Si P S SUPERNOVA Gravitación Fe C. THIBAULT (CSNSM) 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… White Dwarf Main Sequence AÑOS Density/ 109 109 Brown Dwarf Red Giant Massive Stars Supernova Algún 109 segundo 100 kg C. THIBAULT (CSNSM) Spectrum of Cassiopeia We see here the remnants of a supernova in Cassiopeia.This radio telescope picture is taken with theVery Large Array in New Mexico. From the measured rate of expansion it is thought to have occurred 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 part of the gamma ray spectrum with a clear peak at 1157 keV,the energy of a gamma ray in the decay of 44Ti. e.g., Diehl et al., Astron. Astrophys 97, 181 (1993); Publications of the Astr. Society of the Pacific 110:637 (1999) Full-sky Comptel map of 1.8 MeV gammas in 26Mg following 26Al GS b-decay. (a) Spin traps, eg. 26Al, (N=Z=13) 0+ state b-decaying spin-trap. 0+, T=1 5+, T=0 (decays direct to 26Mg GS 228.3 keV, T1/2=6.3 secs via superallowed Fermi b+…forking in rp-process + 26 0 keV, T1/2=7.4x105 yrs (decays to 2 states in Mg via forbidden, Dl=3 decays). Principe de nucléosynthèse Principle of laNucleosynthesis protons 63 65 28 Ni 58 59 60 61 62 64 27 Co 26 Fe 59 29 Cu 54 55 56 57 58 35 30 40 neutrons Il y a compétition Competition between twoentre processes ••Capture Captureof d’un neutron a neutron ••b Radioactivité Radioactivityb– n p + e-+ C. THIBAULT (CSNSM) Part of the Slow Neutron Capture Pathway In Red Giant Stars neutrons are produced in the 13C( 4He,n) 16O or 22Ne(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 at N = 46/50, 76/82, 116/126 They are due to production by the two separate processes S – process & R-process. M74 Gemini M31-Andromeda Galaxy-2.2Mly from Earth, Part of our Local cluster 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. It shows the Sun with the four, inner Terrestrial planets, followed further out by the Asteroid belt then the Gas 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 We again see the solar system below but this time without the Sun. On the right we see the scales of the orbits of the various planets. Distance-109 m The Solar System 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 Convenient Measure of distance -Astronomical Unit(1 au) = Average Earth-Sun distance = 1.496 x 1013 cm = 1.496 x 1011 m 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. Kepler’s Third Law Plot of a3 versus P2 for the planets in the Solar system a3 Asteroids - Here a is in AU and P is in Earth Years. P2 Clearly P2 a3 Asteroids lie in belt from 2-3.5AU from Sun. Reminder:All three of Kepler’s Laws are rigorously obeyed wherever two objects move under their mutual gravitational attraction. Planetary Orbits Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Semi-major axis (106 km) Sidereal Period Orbital Eccent. 57.9 108.2 149.6 227.9 778.4 1424 Surface Temp. 5906 0.241 0.615 1.0 1.88 11.9 29.5 84.0 165 248 0.21 0.05 0.06 0.05 0.01 0.25 Direction of revn Angle to plane 7.0 to ecliptic(degs.) Angle of Plane 0.1 to spin axis(degs) Rotation Period (Days) 2871 4499 0.01 0.02 009 They are all the same apart from Venus 1.3 2.5 0.8 1.8 17.1 178 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 58 58 50 86.8 102 0.013 Mass(1024 kgm) 0.33 3.4 0 1.8 97 4.87 5.98 0.64 1900 569 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 supernova or 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 when the collapse starts then it will speed up as it gets smaller in order to conserve angular momentum. Formation of Solar System Protoplanetary disc or Proplyd 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. 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 heavy Elements. 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 planets are 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 icy grains on outside grew together and then accumulated gases. Note:- Chemical differentiation vs. heterogeneous accretion Former - 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 protosun formed 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,Mg S,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 Hubble space telescope pictures of star-forming region in the Eagle Nebula. About 1 light year Enlargement of regions where young stars are forming. Tips are about size of the Solar system. Origin of the Solar System A small part of the ORION nebula In which young stars are being formed 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. Size of Solar system Protoplanetary discs forming in the ORION Nebula. Insets show examples. They are In false colour and the picture is a mosaic of HST pictures. A young star is at centre of each proplyd. Jovian Planets Outer planets probably began in same way with accretion of planetesimals. Since T was 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 planet Planet 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 detect a 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 Planet Variety 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. Summary Extrasolar 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, rather cooler 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 to a collapse in the magnetic field with a large release of energy. This heats the plasma and accelerates the charged particles to high velocity. Solar Prominence UV photo of this very Large solar prominence. It is 20 times Earth size. Courtesy of A..King Courtesy of A.King Mercury Mass = 3.3 x 1023 kg Distance from Sun = 0.307 – 0.467 AU Orbital period = 87.97 days Rotational Period = 58.6 days Density = 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 makes three 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 AU Mass = 4.869 x 1024 kg Orbital Period = 224.7 days Rotational period = 243 days Density = 5243 kg/m3 Surface temp = 733K Surface Pressure = 90 atmospheres Covered by a thick, unbroken layer of clouds. It rotates in retrogade rotation Clouds are transparent to radiowaves and microwaves. Large number of space probes aimed at Venus Strong greenhouse effect so surface is hot. Russian Venera-14 Satellite landed And we see surface Venus-Second Planet out Terrestrial Type planet. Covered in thick cloud of ammonia etc. Surface is rocky As we can see on the radar maps. Density similar to Earth. Volcanic activity is probably responsible for Injecting substantial amounts of sulphuric Acid 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 kg Distance to Sun = 1.496 x 108 km Density = 5515 kg/m3 Surface Temperature = 333K Orbital period = 365.256 days Rotational 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. 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 solidified again apart from outer liquid core it had a layered structure. As the outer layers cooled large cracks developed in the lithosphere because of thermal Stress-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. Aesthenosphere Is plastic and kept so by heating from radioactive decay.. Very slow convection then provides 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 vertical T 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 Coriolis Effect. 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 axis Remember 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 their magnetism 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 particles is the solar wind. They are responsible for Aurora. Earth’s Magnetosphere Solar wind = stream of ionised gas from Sun. velocity = approx 400 km/second It 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 prevents the 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. Earth Observation U.S.A. at night from space. Mount Etna from space 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 mass Mean distance = 384,000 km Diameter = ¼ x Earth’s diameter. Orbit eccentricity is approx 0.05 Daytime T = 373 K Nightime T = -160K No atmosphere to store heat. Density = 3.4 g/cc Apollo rock samples show material is as old as Solar system. They are older than Earth rocks because of Volcanic activity here. Structure of Interior Largely dead geologically No magnetic field in essence Maybe in past it was bigger. Any seismic activity due to tidal effects. Craters from meteor impact Early molten stage Vulcanism 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-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. Mars from Viking 2 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 case of the Moon. This process stopped when all the debris in the solar system had been Mopped up. Surface Atmospheric pressure = 1/200 atmosp. pressure on Earth Atmosphere = 95% CO2 plus 5% N Large Dust Clouds due to seasonal heating Frozen carbon dioxide at Pole Variation in temperature at site of Viking 1 Valles Marineris 500 m wide and up to 6 km deep. Jupiter Mass = 1.899 x 1027 kg Distance from Sun = 4.95 – 5.455 AU Orbital period = 11.86 years Rotational period = 9 hours 50 mins Diameter = 133.7 – 142.98 x 106 m Average 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 Giant Jupiter has a volume approx 1000 times the Earth’s volume..The mass = 1.9 x 1027 kgm Diameter is 142,800 kms. It has a very dynamic weather system-atmospheric clouds,storms and latitudinal bands. 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 the whole planet. It is very like the Sun. It is composed mainly of H and He with small amounts of Methane, ammonia, water vapour and other compounds. At great depths the pressure is very high and atoms are broken up. In this state H becomes a metal. The Great Red Spot The four Galilean Satellites They all orbit more or less in plane of planet’s orbit. Their motions are closely linked. The tidal effects are very strong. They all rotate in same direction as orbit. Large number of other satellites. Although all of “publicity” is for Saturn’s rings 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 Galilean Moons are Amalthea(top), Metis and Adrastea(to right) and Thebe(left). Jupiter’s rings and moons exist within an intense radiation belt of ions and electrons trapped in the planet’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 spread Over 1017 square km. Largest is CERES with diameter Of 934 km. It accounts for 1/3 of total Asteroid mass. Probably planet did not form because of huge pull of Jupiter. They occasionally collide with each other and 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, also typical of such small objects. Solar System Schematic view of the solar System. The insets show a COMET and an ASTEROID Note the asteroid belt between Mars and Jupiter Further out we have the Kuiper belt and much further away 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 warmNoon 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 planets0.7-2.0 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 recently Discovered 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 of Jupiter-like mass but they fall into two groups-those very close in and those a long way out. So far we have no explanation of this. Telescopes 1022 m 1019 m 10-15 m 10-14 m 10-10 m 10-9 m 1012 m 107 m 10-6 m 10-5 m Microscopes