The formation of stars and planets

1. The formation of stars and planets Day 5, Topic 1: The Solar System and Extrasolar Planets Lecture by: C.P. Dullemond

2. The Solar System

3. The Solar System

4. The Solar System • Inner rocky planets: Mercury, Venus, Earth, Mars • Asteroid belt • Gas Giant Planets: Jupiter (5.2 AU), Saturn (9.5 AU), Uranus (19 AU), Neptune (30 AU) • Edgeworth-Kuiper Belt Objects: icy bodies, some of which are nearly ‘planets’, some of which qualify as comets. Biggest KBOs: Pluto-Charon, Sedna, Quauar, unnamed new object. • Oort cloud: nearly spherical swarm of comets, originally formed in outer solar system, then kicked out by Jupiter, but still marginally bound to solar system.

5. The Solar System Titius-Bode relationship of planet distances:

6. Gas giant planets: Jupiter & Saturn • Dominant composition: • Hydrogen + Helium, like the sun • Surface clouds: ammonia ice, water ice.... • Deep in interior: liquid metallic hydrogen • Even deeper: rocky core of ~ 10...15 M • These are model results which depend on equation of state of hydrogen • For Saturn this is certain (unless models are wrong) • For Jupiter the uncertainty includes Mcore=0

7. Ice giant planets: Uranus & Neptune • Dominant composition: • Water + Ammonia + Methane ices • Only atmosphere contains H, He (in total only minor) • Uranus: • 25% Iron + Silicates • 60% Methane + Water + Ammonia • 15% Hydrogen + Helium • Neptune: • 20% Iron + Silicates • 70% Methane + Water + Ammonia • 10% Hydrogen + Helium

8. Interiors of Jovian Planets: cross-cuts

9. Thermal emission of Jupiter and Saturn • Jupiter and Saturn emit more radiation than they receive from the sun. • They are not massive enough for nuclear burning (need at least 13 Mjup) • Kelvin-Helmholz cooling time scale much shorter than current age (at least for Saturn) • Possible solution: • Helium slowly sediments to center, releases gravitational energy

10. Formation of the solar system

11. Formation of the Solar System • Formed 4.568 Gigayears ago (=age of oldest known solids in solar system) • Mars formed about 13 Megayears later • Earth formed 30 to 40 Megayear later • Leading theory for formation of the moon is that about 100 Myr after the birth of the solar system Earth was hit by a Mars-size object. The heavy cores of both objects formed the new Earth and the light silicate crusts formed the moon. • Jovian planets (Jupiter, Saturn, Uran, Neptune) must have formed in less than 10 Myrs (life time of gaseous protoplanetary disks)

12. Why U+N ice, J+S hydrogen? • Theory: • All four formed at similar location, first forming a rock+ice core by accumulating icy bodies • Somehow U + N were moved outward and did not accrete much gas anymore • J + S remained and accreted large quantities of hydrogen gas

13. ‘Minimum mass solar nebula’ By looking at the mass distribution in the solar system, Hayashi (1981) concluded that the protoplanetary disk of our own solar system had to have (at least) the following mass distribution: Fsnow is the solid mass enhancement due to freeze-out of water onto the grains.

14. ‘Minimum mass solar nebula’ rock rock+ice

15. ‘Minimum mass solar nebula’ rock rock+ice Our planets overplotted: Mplanet/R Box = planet, cross = estimated rocky core

16. Meteorites: Messengers from the early solar system

17. Meteorites • Most famous: Allende • Fell in Chihuahua Mexico in 1969 • Huge fireball and shower of stones • About 2000 Kg of rock collected • Biggest rock was 100 Kg • Sometimes angle of infall can be reconstructed from camera recordings. Orbit of meteorite can then be reconstructed (very important!) • Meteorites often easier to find on ice fields on polar caps (Antarctica)

18. Chondrites Meteorites Trieloff & Palme Review (2005) • Some meteorites originate from mars or moon • Most meteorites were originally part of ~100 km sized planetesimals (`parent bodies’) that have fragmented. • Some are from differentiated parent bodies: heat has melted the material: iron sunk to center: iron meteorites, basaltic meteorites. • Most are from undifferentiated parent bodies: original build-up particles still recognizable: • Chondrules (mm size spherules) • Matrix (`cement’ between chondrules: <10 m particles) • Calcium-Aluminium-rich Inclusions (CAIs, cm size, rare)

19. Chondrules+Matrix

20. Chondrules+Matrix

21. Classes of Chondrites • Chondrites (or ‘chondritic meteorites’) named after their abundant constituents: chondrules • Two main classes of chondrites: • Ordinary chondrites (most abundantly found on Earth) • Carbonaceous chondrites: fewer chondrules, more matrix (30%-100%) • Many sub-classes of chondrites, for instance: • Iron (Fe) content: H (high), L (low), LL(low metal) • Mn,Na,Zn content: CI (high), CM, CO, CK, CV (low)

22. Properties of matrix • ‘Cement’ between chondrules • Consists of micron size particles • Often contains water and carbon • Often contains hydrous minerals resulting from ancient interaction of liquid water and primary minerals: • Serpentine • Smectite • Carbonate Must have been liquid water in planetesimals!

23. Properties of chondrules • Rounded, once molten silicate droplets • Their formation requires T>=1600K • Formation process is still unclear! • Their composition varies from meteorite to meteorite, but the average composition (chondrules+matrix) appears to be solar (chemical complementarity between chondrules and matrix). • Used as argument that they must have formed at the same time through the same process

24. CAIs Allende

25. Properties of CAIs • Calcium-Aluminium rich • First elements to condensate when cooling down from high temperatures • Must have formed at high temperature (~2000 K) • Oldest solids in the solar system (1 to 4 Myear older than most chondrules) • Their formation is still unclear! • Refractory minerals

26. CAIs Mystery: how can CAI contain chondrules if they are supposed to be older than chondrules?

27. Radiometric age determination • Various methods involving long-lived nuclides: • U-Pb-Pb method • K-Ar method • At high temperatures the decay products can easily diffuse out of minerals (i.e. get lost or equilibrate with neighboring minerals). • Once temperature drops below the so-called closure temperature, the decay products get trapped. • Ratio of parent and daughter nuclides gives time since drop below closure temperature

28. Short-lived nuclides • Short-lived nuclides at birth of solar system • Example: 26Al is a short-lived nuclide. Has a half-life of 0.73 Myear. Decays into 26Mg. • How do we know? • Observation: In single meteorite, but in different minerals: find different 27Al abundances. But ratio of 27Al /26Mg always the same. • Explanation:26Mg is the decay product of 26Al. • How can they have been there? • Energetic protons from early sun: e.g. p + 25Mg  26Al. • Enriched supernova/AGB-wind material entrained in pre-SS-core material, and at the same time triggered collapse of core to form the solar system.

29. 26Al-heating of parent bodies • 26Al is a short-lived nuclide: has a half-life of 0.73 Myear. Decays into 26Mg • Time of formation of parent body determines abundance of 26Al. All this nuclear decay energy is converted into heat within couple of Myear, and takes ~100 Myr to diffuse to surface and radiate away. • Conclusion: peak temperature is determined by formation time of parent body. • Peak temperature affects minerals: can be deduced from meteorite: • Too hot: differentiated parent body • Too cold: no metamorphism (contrary to observed)

30. Many fundamental open puzzles • Why do almost all meteorites consist of mm size chondrules, and how are they formed? Need high temperature and quick cooling: • Impacts? Lightning? Shocks? • Why do chondrules and matrix have different composition from meteorite to meteorite, yet be chemically complementary? • Must have formed quickly and locally • What is the origin of CAIs? • In inner regions of accretion disk? Transported outward by X-wind? • Oxygen isotope problem

31. Extrasolar Planetary Systems

32. Radial velocity detection of planets Radial velocity measurements: From: Review by G. Marcy Ringberg 2004

33. Transiting Extrasolar Planets From: Review by G. Marcy Ringberg 2004

34. Detection via microlensing OGLE-2003-BLG-235 Foreground faint (invisible) star passes across background faint (invisible) star. Gravity of foreground star amplifies background star. Brightening of background star. If planet is present around foreground star, AND one is lucky that it also passes background star: one sees ‘blip’ in the signal.

35. Detection via microlensing OGLE-2003-BLG-235

36. Masses of Extrasolar Planets From: Review by G. Marcy Ringberg 2004 Butler et al. McArthur et al. Santos et al.

37. Eccentricity of Planets From: Review by G. Marcy Ringberg 2004

38. Laughlin Two-planet system: Gliese 876 From: Review by G. Marcy Ringberg 2004

39. mean motion resonances Multiple Planetary Systems From: Review by G. Marcy Ringberg 2004 15% of detected planetary systems are known to be multiple

40. Relation Planets and Metallicity From: Review by G. Marcy Ringberg 2004 Abundance Analysis of 1000 stars on planet search . 1.6 Pplanet ~ (NFe/ NH) Model: Kacper Kornet et al. Fischer & Valenti 2005 Previous Evidence: G.Gonzales, N.Santos

41. Hot Jupiters