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The solar system

The solar system. • Earth and Moon • Telluric planets • Jovian planets… • … and their moons • Small bodies. Earth and Moon. A unique couple R Moon = 0.27 R Earth M Moon = 1/81 M Earth Special case in the solar system R Titan = 0.043 R Saturn

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The solar system

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  1. The solar system • Earth and Moon • Telluric planets • Jovian planets… •… and their moons • Small bodies

  2. Earth and Moon A unique couple RMoon = 0.27 REarth MMoon = 1/81 MEarth Special case in the solar system RTitan = 0.043 RSaturn MTitan = 1/4400 MSaturn RTriton = 0.056 RNeptune MTriton = 1/4700 MNeptune Le couple Terre – Lune vu par Galileo

  3. A B C Moon Earth gravitational attraction centrifugal force Earth and Moon - 2 Tides Gravitational attraction of Moon FA > FC > FB→bulges on Moon side and opposite side (same for Sun with a 46% strength) • ocean tides (up to 15 m) and continental tides (30 cm)

  4. A C B Moon Earth rotation Earth Earth and Moon - 3 Effects of tides on the Earth – Moon system (1) Earth rotation carries the tidal bulges Moon attraction on the bulges slows down Earth rotation Conversely, the orbital motion of the Moon is accelerated

  5. Earth and Moon - 4 Effects of tides on the Earth – Moon system(2) Lunar tides caused by Earth attraction (stronger) → slowing down of Moon rotation, until synchronisation with orbital motion → always the same side towards Earth Visible side and hidden side of the Moon

  6. Earth and Moon - 5 Effects of tides on the Earth – Moon system (3) Now: • day’s length increased by 1 minute every 4 millions years • Moon gets 3.7 cm further each year 400 millions years ago, length of day was 20 h When rotation of Earth will be synchrone (in a few dozen billion years) it will rotate in 47 present days

  7. Earth and Moon - 6 Peculiarities of the Earth – Moon system Earth is the only telluric planet with a genuine satellite Among all solar system satellites, our Moon is unique because: • its orbit does not coincide with the planet’s equatorial plane • its large size compared to the planet Moreover, the Moon was closer to the Earth in the past → suggests a formation scenario different from the other satellites Neptune Earth Triton Moon

  8. Earth and Moon - 7 Formation scenario for the Earth – Moon system 100 million yeras after its formation, the proto-Earth would have collided with another proto-planet, of size similar to Mars → debris ring around proto-Earth → debris start to stick together → formation of a big moon close to the planet Then, gradually, the two bodies move further away

  9. Earth and Moon - 8 Internal structure of the Earth (1) Mean density ≈ 5.5 (5500 kg/m3) – Density earth crust ≈ 3 → cannot be made of the same rocks in its whole volume Earthquakes → seismic waves Propagation: depends on the medium crossed → allow to model the Earth interior

  10. Earth and Moon - 9 Internal structure of the Earth (2) Continental crust (granite) – oceanic crust (basalt) Mantle (olivine = heavy silicate) • rigid in upper layers • viscous below Metallic core (iron, nickel,…) • external (liquid, T≈ 3800 – 4200 K) • internal (solid, T≈ 4200 – 4300 K)

  11. Earth and Moon - 10 Plate tectonics Convection in mantle → displacement of the crust → continental drift → volcanism

  12. Earth and Moon - 11 Dating rocks Time elapsed since rock solidification: Measured by radioactive clocks Half-life: T½ = time for half of the nuclei to disintegrate The proportion of children / parents nuclei increases with time ParentChildT½ (109 yrs) 40K 40Ar 1.3 238U 206Pb 4.5 232Th 208Pb 14.0 87Rb 87Sr 48.8

  13. Earth and Moon - 12 Earth’s age Age of oldest • terrestrial rocks: 4.0 billion years • lunar rocks: 4.4 • meteorites: 4.6 Most solar system bodies probably formed at the same time → Earth’s age = meteorites age Terrestrial rocks: appear younger because they experienced fusion phases during the first hundred billion years

  14. Earth and Moon - 13 Terrestrial magnetism North Magnetic Pole (NMP) 20° from North Geographic Pole Continuously moves, on average 40 m per day Analysis of different age rocks → displacement of NMP during geological eras (polarity inversions) Cause of magnetism: Rotation of the outer metallic core (partly ionized) faster than crust → `dynamo effect´

  15. vent solaire Earth and Moon - 14 Magnetosphere Earth’s magnetic field extends through space `Shield´ which deflects solar wind charged particles → essential for life on Earth Capture of charged particles → Van Hallen belts Particle overflow → enter the atmosphere close to the magnetic poles → polar auroras

  16. e– E hν Earth and Moon - 15 Polar auroras (1) Collision of charged particles with atoms of upper atmosphere → excitation of atoms The excited e– falls back to the fundamental level while emitting a photon

  17. Earth and Moon - 16 Polar auroras(2) Green color: atomic oxygen (577.7 nm) (altitude ~100 km) Purple-red color: nitrogen molecules N2

  18. Earth and Moon - 17 Earth’s atmosphere (1) 75 % of its mass in a 10 km layer Composition: N2 78 % O2 21 % Ar 0.9 % CO2 0.04 % H2O 0 – 4 %

  19. Earth and Moon - 18 Earth’s atmosphere (2) Compared to those of Venus (96% CO2) and Mars (95% CO2) Earth’s atmosphere has a very peculiar composition That peculiarity is related to: • oceans (dissolve CO2) • life: Plants photosynthesis converts CO2 in O2 → close link between life and atmospheric composition

  20. b a f Earth and Moon - 19 Earth’s orbit Sidereal period: 365.26 days Angle equator – orbit: 23.5° Mean orbital radius: 149.6 ×106 km = 1 astronomical unit (AU) orbital eccentricity: e = 0.0167 Excentricity:

  21. Earth and Moon - 20 Moon’s orbit Mean orbital radius: 384 000 km Angle equator – orbit: 2.6° Sidereal period: 27.3 days Angle orbit – ecliptic: 5.1° Synodic period: 29.5 days (٪Sun → phases → month) Orbital eccentricity: e = 0.0549 Elliptical orbit + angle equator – orbit → apparent oscillation (libration) → 59% of Moon’s surface is visible

  22. Earth and Moon - 21 Characteristics of Moon • No atmosphere → no erosion • meteoritic impacts → craters • `marias´ and `highlands´ • Fully cooled → no tectonic activity • Mean albedo: 7 %

  23. The telluric planets PlanetM R g D eTyrTday Mercury 0.056 0.38 0.38 0.39 0.21 88j 59j Venus 0.82 0.95 0.90 0.72 0.007 225j –243d Earth 1.00 1.00 1.00 1.00 0.017 365j 23h56 Mars 0.11 0.53 0.38 1.52 0.093 687j 23h37 M = mass R = radius g = acceleration of gravity(surface) D = mean distance to Sun (all with respect to Earth) e = orbital eccentricity Tyr = revolution period Tday = rotation period (sidereal day)

  24. The telluric planets - 2 Mercury No atmosphere, except H et He captured from solar wind, P~ 10–12 bar Orbital eccentricity: e = 0.206 Rotation : 59 d = 2/3 of year → gravitational resonance 1 rotation ½ over itself between 2 perihelion passages → always a tidal bulge towards the Sun at perihelion → faces alternatively hot and cold Mercury imaged by Mariner 10

  25. The telluric planets - 3 Venus (1) Thick atmosphere, P~ 90 bar, density ρ~ 0.1, Tsurface~ 480°C CO2 (96%) – N2 (3.5%) H2O – SO2 – H2SO4 (traces) Greenhouse effect increases T by 500 K SO2 → volcanic activity Retrograde rotation → collision with another planet? (but, then, why e≈ 0?) Resonance with earth (5 orbits of Venus between each alignement) Venus in visible light (Galileo)

  26. The telluric planets - 4 Venus (2) Opaque atmosphere → reconstruction of surface relief by radar measurements from probes orbiting Venus (Magellan, 1990) Reconstruction of Venus surface by radar measurements (Magellan)

  27. The telluric planets - 5 Mars Tiny atmosphere, P~ 0.008 bar, Tsurface~ –140 (night) to +20°C (day) CO2 (95%) – N2 (3%) – Ar (2%) H2O – O2 (traces) g too low to effectively retain the atmosphere Polar axis inclined (25°) → seasons Polar caps : H2O + CO2 Weather: sandstorms Mars seen from Earth (HST)

  28. The telluric planets - 6 Martians 1877 : Schiaparelli sees straight lines on Mars surface 1894 : Lowell builds an observatory and observes the same lines Channels built by Martians to irrigate dry lands with water from the polar caps! 1970: Mariner probes → channels don’t exist `Channels´ on Mars and a recent picture

  29. … at better resolution The telluric planets - 7 Other martian fantasmagories 1976 (Viking 1) : structure resembling a human face 2001 (Mars Global Surveyor): where is it gone?… `Face´ on Mars…

  30. Mars or Southern Morocco? The telluric planets - 8 Mars landscapes Since 2002, `Spirit´ and `Opportunity´rovers (and `Curiosity´ since 2012) explore Mars → harvest of pictures Mars = arid desert, with sandstorms from time to time Martian landscape

  31. The telluric planets - 9 Water on Mars? No surface liquid water in present conditions Numerous gullies: depth~ few m width~ few 10 m length ~ few km (much too narrow to account for Sciaparelli observations) + remains of river systems → water must have flown on Mars in the past, when the atmosphere was thicker Gullies observed by MGS

  32. The telluric planets - 10 Life on Mars (1) 1976: 2 Viking probes land on Mars at median latitudes (température from –170 to +few °C) Soil samples → 4 experiences to detect signs of life • no organic molecules (< 1/109) • search for chemical changes due to living organisms (soil samples placed in nutritive environments) : slight changes observed not due to life according to specialists Viking mission

  33. The telluric planets - 11 Life on Mars (2) 1996: analysis of a meteorite found in Antarctica in 1984 • fragment of Mars crust ejected by a big meteorite impact some ~15 millions years ago, fallen on Earth some ~15000 years ago • some scientists claim that microscopic structures in the meteoritewould be remains from a primitive life form • it could have appeared some 3.5 billion years ago, under a thicker atmosphere plus dense and with liquid water → life on Mars: controversial subject Meteorite ALH84001

  34. The telluric planets - 12 Mars satellites Phobos and Deimos (sons of Ares): 2 captured asteroids (27 and13 km) TPhobos < Trot(Mars) → tidal effects reverse from Earth – Moon system → Rorbit decreases → Phobos will crash on Mars (in ~108 years) Phobos (MGS) Deimos (Viking)

  35. Jovian planets PlanetM R g D eTyearTday Jupiter 318 11.2 2.5 5.2 0.048 11.9yr 9h55 Saturn 95 9.3 1.1 9.5 0.056 29.5yr 10h39 Uranus 15 4.0 0.9 19.2 0.046 84.0yr 17h Neptune 17 3.9 1.1 30.1 0.010 164.8yr 16h M = mass R = radius g = acceleration of gravity (surface) D = mean distance from Sun (all with respect to Earth) e = orbital eccentricity Tyear = revolution period Tday = internal rotation period

  36. The jovian planets - 2 General properties • Made of a fluid, which density increases with depth (gradual transition gas → liquid) • Probably small core made of rocks and metals • Differential rotation of atmosphere (vequator > vpole) • Strong magnetic field → allows to measure internal rotation

  37. The jovian planets - 3 Jupiter Upper layers:H2 (78%) + He (20%) + CH4 + clouds of NH3, NH4SH, H2O Cloud color: solid particles (sulfur, methane compounds) Great red spot: huge storm (2 × Earth size) discovered by Robert Hooke (1664) = high pressure zone Jupiter emits more energy than it receives from the Sun (gravitational contraction) Jupiter (Cassini)

  38. The jovian planets - 4 Dive into Jupiter’s interior Gradual increase of pressure and temperature • gaseous H2 et He + clouds (2) gradual transition to liquid H2 + He (~0.75 RJ) (3) dissociation of H2 followed b y ionization of H → metallic hydrogen → strong magnetic field (17000 × terrestrial field) (4) Core of H2O, NH4, rocks, metals (1% of total mass) Region of the Great Red Spot

  39. … and their moons - 5 The moons of Jupiter 16 moons including 12 captured asteroids 4 largest: discovered by Galileo in 1610 MoonM(MM) R(RM) T(d) g(ms-2) Io 1.2 1.05 1.8 1.8 Europe 0.7 0.9 3.6 1.4 Ganymede 2.0 1.5 7.2 1.5 Callisto 1.5 1.4 16.7 1.2 All in synchroneous rotation (tidal effects) T°~ –150 °C The 4 galilean moons

  40. … and their moons - 6 Io (1) D = 420000 km from Jupiter Most active volcanism in the solar system Eruptions of S and SO2 and not H2O and CO2 as on Earth (probably exhausted) Volcanism caused by tidal effects (perturbations from other moons → oscillations around the equilibrium position → frictions → heat) Io (Galileo)

  41. … and their moons - 7 Io (2) Surface constantly renewed by volcanic ashes Gas ejected at v > 1 km/s, part of it escapes and forms a ring around Jupiter Io in April and September 1997 Volcanic eruption on Io

  42. … and their moons - 8 Europa (1) D = 670000 km from Jupiter Very smooth surface (features < 1 km) composed of ices (mainly H2O, with NH3, CO2) Model: • Metallic core • Rocky mantle • Ocean of water or mud (life?) • Ice crust (thickness ~100 km) Europa (Galileo)

  43. … and their moons - 9 Europa (2) Few craters → surface rapidly regenerates → crust not too thinck, nor too rigid Covered with cracks 10 to 80 km broad, up to 1000 km long Impact on Europa Surface of Europa

  44. … and their moons - 10 Ganymede (1) D = 1070000 km from Jupiter Biggest moon in solar system Density: ρ~ 0.5 ρMoon → ± 50% ice → prototype of `ganymedian´ objects (as all giant planet moons, except Io and Europa) Ganymede (Galileo)

  45. … and their moons - 11 Ganymede (2) Surface partly coverded by grooves a few hundred meters deep Current explanation: Ganymede still cooling → phase transition: water → ice → increase of volume → cracks filled up by new ice Surface of Ganymede

  46. … and their moons - 12 Callisto D = 1840000 km from Jupiter Ganymede `little brother´ No big cracks → thicker crust Craters → `Icy´version of our moon Callisto (Galileo)

  47. The jovian planets - 13 Saturn Chemical composition similar to Jupiter (1) density ρ < 1 (2) fast rotation → flattening ~10 % Emission of energy more efficient than Jupiter : lower temperature → helium droplets falling towards the core → energy from phase transition + gravity Saturn (Voyager 2)

  48. The jovian planets - 14 Seasons on Saturn Contrary to Jupiter, Saturn’s equator is significantly inclined with respect to orbit (27°) → seasons → rings seen under different angles from year to year → seen by Galileo but not by Huygens, who found the correct explanation Saturn (HST)

  49. The jovian planets - 15 Saturn rings Rings present around all jovian planets, but by far the most massive and bright around Saturn Composed of rock and ice blocks of various sizes (from a dust grain to a few meters) Estimated thickness ~ 10 m Distance: 70000 to 140000 km from Saturn center High albedo (~ 0.6) Total mass ~ 1020 kg Saturn rings (Cassini)

  50. A C R d MP RP The jovian planets - 16 The Roche limit (1) dmin for a satellite whose cohesion is due to its own gravity Tidal force: (on a mass element) Gravitational force (cohesion) :

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