Transcript Quantum Well Electron Gain Structures and Infrared

Extra-Solar Planet Populations
Stephen Eikenberry
4 November 2010
AST 2037
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Radial Velocity Planet Searches
• So … need a speedometer to measure star velocity versus
time
• To a precision of a few meters per second!
• Across distances of many light years!!!
• How? Doppler shift
of spectral lines
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51 Pegasi
• In 1995, Mayor & Queloz announce the discovery of
an orbital signature with amplitude = 50 m/s in a 4.23day period around star 51 Pegasi
• Mass = 0.5 MJUP  First extra-solar planet
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51 Pegasi: Hot Jupiter?
• At that location, expected
temperature is VERY
high (about 2000K or
higher!)
• So … Jupiter-like planet,
but closer than Mercury
 “Hot Jupiter”
• How do you make
something like that????
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Planet Bonanza
• Geoff Marcy & Paul Butler quickly confirmed 51
Pegasi
• They had lots of archival data from searches for
Jupiter-type planets (periods >10 years, so they were
still “in progress”)
• No on even thought to look for short-period MASSIVE
planets (why would they be easier?)
• Found many “Hot Jupiters” – most extra-solar planets
known today are Hot Jupters
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ES-Planet Population
• As of this morning, 228 861 planets are now known to orbit
other stars (!!)
• All of this has happened in about 15 years – someone
currently finds a new planet every couple of days or less
• These planets are NOT generally like our Solar System
objects – WHY?
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Upsilon Andromedae
• First multiple planet system
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Upsilon Andromedae
• First multiple planet system
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HD 209458
• Another Hot Jupiter
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HD 209458
• What is a “transit”?
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HD 209458
• A transit observed
• Note: only ~1% dip
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HD 209458 - Results
• Just at the entry moment into transit, for a brief
instant, only the upper atmosphere of the planet
absorbs any starlight
• With a powerful enough spectrograph, we can look for
absorption lines at this instant
• Result: COMPOSITION of the planet atmosphere
• HD 20948b contains – WATER!!
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Gliese 581c
• Low-mass planet, with mass  5 Mearth
• Orbit semi-major axis 0.07 AU
• Low-mass star
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Gliese 581c
• Just inside Habitable Zone
• Gliese 581d just outside HZ
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Eccentricity
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Circumbinary Planets
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Transiting Planets in the HZ
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Orosz et al. 2012
Image Credits: NASA
Borucki et al. 20
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Planets in Habitable Zones
• Many planets are
currently known in the
Habitable Zone around
their parent stars
• Most of these are gas
giants  no solid surface
• But … gas giants in our
Solar System have lots of
moons
• What happens to Europa
if you move it/Jupiter to a
distance of 1 AU?
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Planets in Habitable Zones
• What happens to Europa
if you move it/Jupiter to a
distance of 1 AU?
• Really?
• Europa mass is closer to
our moon’s mass – why no
water there?
• So … need giant planets
in the HZ with giant
moons …
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Our Solar System is Not
Typical
• Sun is an unusually massive star
• Our solar system has no planets with orbital periods
less than Mercury
• Our inner solar system does not have a
super-Earth-size to Neptune-size planet
• Most planetary systems don’t have a Jupiter analog
→ Planet formation theories should typically
produce planetary systems unlike our own
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Borucki+ 2011; Batalha+ 2012; Howard+ 2012; Fressin+ 2013; Burke+
Terrestrial Planet Finder
• Ultra-high-contrast imager satellite
• Capable of finding Earth-mass planets in HZ around nearby
stars
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Summary
• We have found hundreds of planets around other stars
• Overwhelming majority are massive gas giants, many close
to their parent star
• This is because they are easiest to find with the Doppler
technique; but Kepler mission (transits) is changing that
• Have found: multiple planet systems (20+); planet
atmospheres; some low-mass (probably solid) planets
• Eccentricity seems more common than circular orbits;
problems for life
• So far, only a few gas giants in the HZ; first possibly-solid
planets; maybe moons could host life (??)
• Future searches will be sensitive to Earth-mass planets in
the HZ
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Exoplanet Zoo: Examples
• We have found
hundreds of planets
around other stars
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Exoplanet Zoo: Examples
• Multiple-planet systems
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Exoplanet Zoo: Examples
• OGLE-2005-BLG-390Lb – 5.5 Earth-mass, far from star
(T=-360 ˚F)
• COROT-7b: 4.8 Earth-mass, density = Earth-density (!);
close to star (T ~1300K)
• Gliese 581g: 3-4 Earth-mass; T ~- 25 ˚F to +160 ˚F; in the
Habitable Zone (!), but tidally locked
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