Extra-Solar Planet Populations Stephen Eikenberry 4 November 2010 AST 2037 1.
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Transcript of Extra-Solar Planet Populations Stephen Eikenberry 4 November 2010 AST 2037 1.
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!!!
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• How? Doppler shift of spectral lines
51 Pegasi• In 1995, Mayor & Queloz announce the discovery of
an orbital signature with amplitude = 50 m/s in a 4.23-day 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
Image Credits: NASA Borucki et al. 2012Orosz et al. 2012
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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
Borucki+ 2011; Batalha+ 2012; Howard+ 2012; Fressin+ 2013; Burke+ in prep
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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