Download Extrasolar Planets = 403

Extrasolar Planets = 403
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Planets orbiting stars other than the Sun
Smaller than 13 Jupiter masses
First planet around ordinary star is 51 Peg 1995
Most found using Iodine cell technique pioneered at
DAO, UBC, UVic
Zeroth Method:
Pulsar Timing
• First planets discovered
• By Wolszczan in 1989
• Would have been inside
supernova explosion
• 2 systems/ 4&1 planets
First Method: Direct Imaging
of Extrasolar Planets (11)
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Planets are billions times fainter than sun/star
Planets usually not resolved from star
Use adaptive optics or HST
HR8799 & Fomalhaut announced Oct08
Second: Astrometric Detection
of Extrasolar Planets
• Stellar motions not resolved
=too small to be measured
• First & only detection
announced 2002
• Gl 876 had previously been
known to have a planet from
radial velocity studies
Third: Gravitational
Lensing Method (9)
• Foreground star lenses background
star and planet(?)
• One 5.5 Earth masses
• At distance of Asteroid belt from
M dwarf
• Frequency of planets larger than
13% - likely 90% for M dwarfs
Fourth: Radial Velocity (376)
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Star pulled back and forth by gravity of planet
Doppler shift measures velocity of star
Bigger, closer planet: larger velocity
Lots of “Hot Jupiters” discovered
The first planet
discovered in the solar
neighborhood in 1995
Fifth: Transiting Planets
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62 transiting planets
Smaller star - deeper eclipse
Bigger planet - deeper eclipse
Observations by Deeg and Garrido at
the 0.9m Sierra Nevada Telescope of
IAA Granada).
Characterization of Planets
• Planets only a million
times fainter in Infrared
• Using the Spitzer IR
telescope the planet’s
eclipse can be seen
• Gives planet temp=770K
• Drawn in Visible and IR
Upper Atmosphere of HD209458B
• Can see the planet’s
atmosphere in
absorption during
transit
• Hydrogen, Na, H2O
gas in atmosphere
blown away by
stellar wind
Atmosphere of
HD209458b
• A dozen eclipsing extrasolar planets
• If you subtract an eclipse spectrum
from an out of eclipse spectrum you
get the planet’s spectrum
• No “bio-markers” (CH4+O2) and
surprisingly no water
Map of Extrasolar Planet 3
• Planet orbits HD189733 showing
phases, assuming locked in rotation
• Winds transport heat to night side?
• Map has temperatures of 650-900C
Extrasolar
Planets
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403 Planets
Orbiting stars
Binaries,Triples
Giants
White Dwarfs
45 multiple planet systems
Most are Jupiter mass planets & close to star = short period
Observed orbits more eccentric than Jupiter & Saturn
Most stars with planets have extra iron, silicon, carbon etc.
COROT Hunting Planets
• Blasted off 27Dec08
• Observes 12,000 stars at a time
• Convection, rotation and
planetary eclipses/transits
• Planetary eclipses are short lines
and spots go in/out of phase
Smallest Exoplanet
• Discovered by CoRoT
2009
• Transit is 0.00035 deep
so diameter ~2Earths
• Radial Velocity =>
~8Earth Masses
• Orbital Period
~20hours
Kepler Satellite
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Launched 06Mar09
Into Earth trailing orbit
Will survey 100,000 stars
Looking for transits by:
1,000 hot Jupiters?
100 hot Earths?
10 Earths in Habitable
zone??
• Marcy will use Keck for
Radial Velocity follow-up
HAT-P-7 b
• First Kepler data
• Shows Eclipse,
Occultation, Phases
• No Earth type
planets; yet
Passing Star
Hypothesis
• Buffon in 1745
• Catastrophic process
• Low probability of
encounter
• Hot gasses would
dissipate before they
could condense
• Predicts few stars
with planets
Nebular Hypothesis
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Descartes 1644 envisioned vortices
Laplace 1796 added Newton’s gravity
Evolutionary process
Angular momentum problem:
Sun has 99.9% of mass and 0.3% of
angular momentum
• Jupiter has 60% of angular
momentum and 0.1% of mass
• All the stars form from dust clouds
• Because cloud is spinning dust falls in
faster along poles forms disk
• Lumps in disk become planets
• Sun and planets clean out inner disk
ending planet building
• Predicts many stars with planets
Solar Nebula
Theory
Stars Form Within Disks
• 2 Million year old star in GMC
• 2MASS shows 2 stars; Adaptive Optics Gemini; Long exposure with
AO and Gemini and close up of thin disk
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5 Disks in Orion Nebula
Solar System Looks Like a Disk
• As the planet’s distance from the sun increases; its period of
revolution about the sun increases & velocity decreases
• The planets revolve in orbits that are tilted less than 7°
• Planets orbit in same direction
Obliquity of Rotation Axes
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Most planets rotate counter-clockwise
Most planets rotation axis is perpendicular to ecliptic plane
Sun’s rotation axis tilted by 7°
But why are Uranus and Pluto tilted ~90°
Why does Venus rotate retrograde=clockwise
Sun and Jovian Planets
• Located in the outer solar system, less dense, more massive, many
satellites, ring systems, thick atmosphere composed with same
chemical composition as sun
Terrestrial Planets and Large Moons
• Earth, Venus, Mars, Ganymede, Titan, Mercury, Callisto, Io, Moon,
Europa, Triton, Pluto
• Located close to sun, more dense, smaller mass, less volatiles, rocky
cratered surface, little or no atmosphere, few moons, no rings
Rocky Surfaces Saturated with Craters
• Planets formed from many meteorite impacts
“Heavy Bombardment”
• Late Heavy Bombardment second surge in impacts
Asteroid
Characteristics
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Vesta, Ceres and Earth’s Moon
Movie of Eros
small rocky bodies
Ceres > 1000km diameter;
2>500km; 15>250km
• Probably a million > 1km
• Named by discoverer
• Not enough gravity to pull them
into spherical shape
Asteroid =
Minor Planet
Orbits
• Some planetesimals left over
after planets formed
• Asteroids, Near Earth Objects,
Comets
• Generally orbit between Mars
and Jupiter with gaps
• Over 444,080 with good orbits
• 1 named after UVic and 14
others named after UVic people
Kuiper Belt Objects •
Small icy worlds beyond
Pluto = Dwarf Planets
• Tenth planet?, Eris=UB313
Comet Lulin
• Dirty Snowball or
Icy Mudball
• Nucleus ~10km
• Tail ~1 million km
• Very eccentric orbit
• 3572 comets – 2000
short period
Comet Tails: Hale-Bopp 1997
• Radiation pressure and the solar wind blow the comet’s tail
• So that it always points away from the sun
• Blue ion/gas tail points away from sun; yellow dust in orbit
Meteorites
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Peekskill meteorite or fireball
1992 New York
Bright as full moon
Lasted for 40 seconds
Meteorite on ground, meteor in air
and meteoroid in space
• Pinhead sized rocks burn up
~80km high in atmosphere
• Earth receives 40,000 tons of
meteorites per year
• Some leftover from formation of
Solar System
Characteristics of Two Kinds of Planets
• Jovian planets are larger, lower density, farther
from sun, thick atmosphere, more satellites, rings
• Terrestrial planets are smaller, denser, closer to sun,
rocky cratered surface, few satellites, no rings
Characteristic Properties- Solar System
• Disk shape of solar system- orbit inclination; prograde motion; nearly
same tilt of rotation axes
• Jovian and terrestrial planet types- low/high density
• Planetary ring & satellite systems for gas giants
• Space Debris – icy comets, rocky asteroids, meteors
• Common ages of Earth, moon, Mars, meteorites, sun
Density of Planets
• Terrestrial Planets more dense than Jovian gas giants
• Uncompressed densities show Mercury is most dense and Mars is
least dense
• Problem is moon is not dense enough (3.36) ???
Hot Disk and Frost Line (Ice Line)
• Gas from solar nebula falls on to disk and heats it
• Beyond the frost line in middle of asteroid belt (~3.5AU)
planetesimals form from water ice
Condensation Sequence
• Generally the closer a planet is to the sun the more metals
• The farther from the sun the more volatile compounds
Condensation
• Shuttle experiment done in no gravity found dust formed
grains very quickly
• If moon formed at same distance: should have the same
density but it does not
Accretion
• Snowballs form aided by static electricity
• Dust falls to form very thin disk and gas
forms thick disk
• Solar wind blows dust around but not
pebbles so dust sticks to pebbles
• Up to kilometer sized
Planetesimals
• Eventually some massive
enough to grow by gravitygreater than ~a km
• Pandora and
• Hyperion; Low density
moons of Saturn
Protoplanets
• The more massive - the faster they grow
• At more than 15 earth masses gravitational collapse starts
• Capturing Hydrogen and Helium directly from nebula
Comet Impacts on Jupiter
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Painting shows Jul94 impacts of Comet Shoemaker-Levy 9
HST photo from 20Jul09
Comets deposit ice
Heating planet
Differentiation of
Planets
• Young planet is very
hot due to radioactive
decay and
• Impact heating (=heat
of formation)
• Iron, Nickel, Iridium
settle to the core
• Silicates rise above iron
• Ices/water next
Outgassing
• Water, carbon dioxide, sulfur dioxide, nitrogen released by
volcanoes
• Forms atmosphere
Overview of Planet Formation
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Common orbital and rotation direction & plane => nebular disk
Jovian / Terrestrial => range of temperatures in disk
Common ages => simultaneous formation in disk
Problems: Speed of Jupiter’s formation, angular momentum,
clearing disk, discrepancies, moon!
Jovian Problem / Disk Instability
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Disk blown away by sun and other stars in a few million years
Jupiter needs to form in millions of years
So Jupiter needs to migrate to sweep up more gas & dust
Movie by Phil Armitage 2005 shows density waves excited by planet
Planet
Migration
• Planetesimals could
gain or loose energy
in encounters with
planets but
• Detailed calculations
show Jupiter would
move in and
Neptune would
move out
• Debris would be
ejected: to Oort
cloud?
Angular Momentum
Problem
• The protosun rotates rapidly and has
huge convection cells so it generates a
strong magnetic field
• The magnetic field tries to accelerate
the disk and solar wind, slowing
rotation by magnetic braking
• Observations of stars with known ages
in Hyades etc. show that the older stars
rotate more slowly
4 Processes that
Cleared the Inner
Solar System
• Radiation pressure sun&stars
• Solar Wind blows away rings
• Planetesimals incorporated
into planets
• Planetesimals ejected
Debris Disk
• After the dense disks that
form planets
• Cold disks of dust are left
• Made from asteroid
collisions & comet’s tails
Heavy
Bombardment Phase
• Heavy bombardment phase at
4 billion years clears nebula
• Craters formed on top of
craters
• Still have problem of tilted
rotation axes: Pluto & Uranus
• Retrograde rotation of Venus
• Eccentric and retrograde
satellite orbits
• Moon
Large Impacts
• In final stages of formation solar
system would have had many
collisions of bodies the size of
planets
• Such impacts could tilt the
rotation axis of Uranus, Pluto +
rotation of Venus
• All planets would have been hit
by something one tenth its size
• Out Beyond the Kuiper Belt at 2000AU to 1 light year
• Lies the hypothetical Oort cloud of a trillion Comets
MOST: Jaymie Matthews UBC
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Observed HD209458 for months and
Saw no eclipses from Earth sized planets
Timed transits showing no Earth sized planets-so far
No opposition effect so low 50% albedo
Coronographic Image of Debris Disk
• Star is masked by black spot in original and untilted image
• Notice cleared inner disk(30AU) and spiral wave features
• ~320 light years distance, 300AU diameter, 5 Million years old
Comet NEAT 29Jan & 2Feb03
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Dirty snowball or maybe icy mud ball is better
Nucleus ~ 10km
Tail ~1,000,000km to 1 astronomical unit
Very eccentric elliptical orbit
Fifth: Transit Method (62)
• Planets of 12 Jupiter masses, Jupiter, Neptune, M
dwarf are all about same size/transit depth
• Works best for big planet close to star
NGC
3603
• Carina Nebula
• Bright young
blue stars
• Red HII
region
• Black Dust
• Two proplyds
dissolving in
UV from hot
stars in about
100,000 years