Download Planet Formation Gas Giants

What is in the Solar System?
Planet Formation
Sun, planets, moons, asteroids, comets, dust…
• The Solar System
• Making a star
• Planet formation
Sun = 99.85% of mass!
Comet West
Eros
Dust
• Rock and ice
• Stopping formation
?
• Extra-solar planets
Reminder: lectures at http://www.star.le.ac.uk/~pto/planets.html
Planets = 0.135% of mass!
Asteroids – interplanetary debris
100,000 known - most between Mars and Jupiter
(>100m are asteroids; rest are meteroids)
• Over
• Total mass < 0.1 Moon. Largest is Ceres (940 km).
• Earth-crossing
• Source
of most meterorites/meteors
Iron & Nickel –
rare, similar to
type M asteroids
Chondrite –
similar to
terrestial
mantle/crust
asteroids are of great interest!
Jupiter
Saturn
Uranus
Neptune
Gas Giants
• Gas+ice+rock core
• Large & massive
• Low density
• Rapidly rotating
• Many moons
• Rings
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Pluto – Dwarf Planet
(God of the underworld)
• Discovered in 1930 during search for Planet X.
• Orbit is eccentric (0.249) and crosses Neptune’s.
• Atmosphere < 10-6 Earth (CH4, N2, CO). Cold!
The Kuiper Belt and Pluto (&TNOs)
Kuiper belt: ~1010 icy objects beyond Neptune (30–1000 AU)
Pluto is a large example.
Quaoar discovered in 2002 – half the size of Pluto. Other
large objects found since (e.g. Sedna, 2003 UB313 (Eris)).
• Low density – 2100 kg m-3; 70% rock, 30% ice.
• Moon Charon (1985) ~1/8 mass of Pluto (+2 small ones?)
Sedna (1200-2000 km size)
The Kuiper belt (KBOs) and Oort cloud
OC extends to 100,000 AU with total mass = 30 x Earth
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Interstellar Molecular Clouds
Cloud fragments to form
multiple “protostars”
Orion nebula
Clouds:
~1014
Eagle nebula
Magnetic field helps
asymmetric collapse.
km, Tcentre~ 10 K, ncentre ~109 particles/m3
Sun: 1.5 x 106 km, Tcentre ~ 107 K, ncentre ~1032 particles/m3
Lots of young stars have disks (+ jets)
Disks are “cool” but also have
regions emitting UV/X-rays these
which destroy many disks/planets
Protostar in <106 yrs – star in 107 yrs
Protoplanetary disks:
“Proplyds”
Cloud to disc
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Beta Pictoris “dust disk”, similar in
size and mass to the Solar System
Planet formation sequence
Planet b orbit
Differentiation of the Solar System
• Plot shows T vs. distance just
before main accretion stage.
• Only the most refractory
materials (e.g. Fe/Ni) remain
solid within ~1 AU.
The Inner Planets
• Within 5 AU dust grains grow to ~1 m in ~1000 years and
accrete into vast numbers of “planetesimals”.
• The biggest planetesimals undergo “runaway growth” to
form the terrestrial planet cores. Their exact chemical
composition depends on their distance from the Sun.
• As protosun grows, contracts
and cools, dust re-condenses –
silicates first.
• At ~5 AU (~Jupiter) disk cool enough for H2O, CH4 etc.
to condense. This is the “ice (or snow) line” for the Sun.
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The Outer Planets
• Beyond snow line ices dominate.
• Density is lower, so get fewer,
more massive embryos (~10xMEarth).
• Extreme runaway growth – they
accrete gas, ice and dust ⇒ giants.
N.B. The outer worlds are not gas-rich.
The inner worlds are light-element poor.
Ending Gas-giant Growth
• Before H-burning, the Sun had an
unstable (T Tauri) phase – high
luminosity and intense solar wind.
• Sun lost ~10 % of mass. Nebula
dispersed halting gas-giant growth.
• Occurred at ~107 years – after
Jupiter/Saturn runaway but before
that of Uranus/Neptune.
• May be why MJ, MS > MU, MN
Ending Terrestrial Growth
• Inner planetesimals perturbed by
Jupiter’s gravity. Fragmentation
follows rather than accretion.
• Some material ejected to large
distances – forms the Oort cloud
and Kuiper belt.
• Gas giants may also have moved
somewhat – migration.
Extra-solar Planets
• Many extra-solar planets.
• Majority are large.
• Majority are close to their
parent star.
• Unlike Solar System.
• Hard to find low-mass
planets using radial
velocity.
• Can find using transits
Kepler mission
http://kepler.nasa.gov
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How to make gas giants close in?
Main
Sequence
stellar
mass
range →
The Habitable Zone
Don’t. Make them far out and migrate. Large planets can
interact with the disk – angular momentum transfer –
moving the planet and creating a gap in the disk.
Result – only a fraction of planets may survive!
HZ is basically where water can be a liquid.
1604: Course test
•
Test paper has 4 questions worth 25% each
•
Paper available via Blackboard after noon on
Monday March 18
•
Submit your answers electronically AND hand in
a printed copy to the teaching office by noon on
Tuesday April 30
•
Marks will be deducted for plagiarism (i.e. you
must rewrite material in your own words)
The End
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