Download The formation of stars and planets

The formation of stars and planets
Day 5, Topic 1:
The Solar System
and
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 System
Titius-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:
3 / 2
 r 
gas  1700 

1AU


g/cm 2
3 / 2
 r 
solids  7.1Fsnow 

1AU


g/cm 2
1,
r  rsnow
Fsnow  
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’
rock
rock+ice
Our planets overplotted: Mplanet/R
Box = planet, cross = estimated rocky core
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
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)
Chondrites
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 preSS-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 a
TIFF (Uncompressed) decompressor
are needed to see this picture.
From: Review by G. Marcy Ringberg 2004
Transiting Extrasolar Planets
From: Review by G. Marcy Ringberg 2004
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.
Detection via microlensing
OGLE-2003-BLG-235
Masses of Extrasolar Planets
From: Review by G. Marcy Ringberg 2004
Butler et al.
McArthur et al.
Santos et al.
Eccentricity of Planets
From: Review by G. Marcy Ringberg 2004
Two-planet system: Gliese 876
From: Review by G. Marcy Ringberg 2004
Laughlin
Multiple Planetary Systems
From: Review by G. Marcy Ringberg 2004
mean
motion
resonances
15% of detected planetary systems are known to be multiple
Relation Planets and Metallicity
From: Review by G. Marcy Ringberg 2004
1.6
Pplanet ~ (NFe/ NH)
Fischer & Valenti 2005
Previous Evidence:
G.Gonzales, N.Santos
Abundance
Analysis of
1000 stars on
planet search .
Model:
Kacper Kornet
et al.
Hot Jupiters