The formation of stars and planets

Day 5, Topic 1:

The Solar Systemand

Extrasolar Planets

Lecture by: C.P. Dullemond

The Solar System

The Solar System

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.

The Solar SystemTitius-Bode relationship of planet distances:

Start +4 /10 Reality:

Mercure 0 4 0.4 0.39

Venus 3 7 0.7 0.72

Earth 6 10 1.0 1.00

Mars 12 16 1.6 1.5

Asteriod b 24 30 3.0 2.8

Jupiter 48 52 5.2 5.2

Saturn 96 100 10.0 9.5

Uranus 192 196 19.6 19.2

Neptune 384 388 38.8 30.0

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

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

Interiors of Jovian Planets: cross-cuts

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

Formation of the

solar system

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)

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

‘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:

€

Σgas =1700r

1AU

⎛

⎝ ⎜

⎞

⎠ ⎟

−3 / 2

g/cm2

€

Σsolids = 7.1Fsnow

r

1AU

⎛

⎝ ⎜

⎞

⎠ ⎟

−3 / 2

g/cm2

€

Fsnow =1, r < rsnow

4.2, r > rsnow

⎧ ⎨ ⎩

Fsnow is the solid mass enhancement due to freeze-out of water onto the grains.

‘Minimum mass solar nebula’

rock

rock+ice

‘Minimum mass solar nebula’

Our planets overplotted: Mplanet/R Box = planet, cross = estimated rocky core

rock

rock+ice

Meteorites:

Messengers from the early solar system

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)

Meteorites

• 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)

Chondrites

Trieloff & Palme Review (2005)

Chondrules+Matrix

Chondrules+Matrix

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)

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!

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

CAIs

Allende

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

CAIs

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

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

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.

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)

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

Extrasolar Planetary Systems

Radial velocity detection of planets

Radial velocity measurements:

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

From: Review by G. Marcy Ringberg 2004

Transiting Extrasolar PlanetsFrom: Review by G. Marcy Ringberg 2004

Detection via microlensingOGLE-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.

Detection via microlensingOGLE-2003-BLG-235

Masses of Extrasolar PlanetsFrom: Review by G. Marcy Ringberg 2004

Butler et al.McArthur et al.Santos et al.

Eccentricity of PlanetsFrom: Review by G. Marcy Ringberg 2004

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

LaughlinLaughlin

Multiple Planetary SystemsFrom: Review by G. Marcy Ringberg 2004

15% of detected planetary systems are known to be multiple

mean motion

resonances

Relation Planets and MetallicityFrom: Review by G. Marcy Ringberg 2004

AbundanceAnalysis of1000 stars

onplanet search

.

1.61.6

PPplanetplanet ~ ~ ((NNFeFe

/ N/ NHH))

Previous Evidence: Previous Evidence: G.Gonzales, N.SantosG.Gonzales, N.Santos

Fischer & Valenti Fischer & Valenti 20052005

Model:Model:

Kacper Kacper Kornet et al.Kornet et al.

Hot Jupiters