The Ancient History of Comparative Planetology
“There are infinite worlds both like and unlike this world of ours...”--- Epicurus (c. 300 BCE) (died painfully 269 BCE) “… false and "There are countless suns and damnable ...” countless earths …” G. Galilei (b. 1564) Giordano Bruno (b. 1584) in De L'infinito Universo E Mondi From Mike Devarian, (life imprisonment JPL (burned at the stake in Campo 1633) dei Fiore, Rome, 1600) An Integrated Program of Planet Finding Science !",$"/ 789:;8<=> ?>=;>8@ (CAD?E7;<7B3825:27 825A87<;A7"5A2=8 01234567839:87;<7 Postponed =5>325>6?7@;A6B8 !"#! indefinitely Outriggers cancelled (CAD?E7;<7:?5A>E7 &,-.# 825A87<;A7BC8275:B7 935:27165:?28 )3B.3:
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!""# !"$" !"$# !"!" !"!# • Ultimate goal: To find Earth-like planets, if they exist, and to search for evidence of life
– So, how do we do that? Exo-Planet Task Force (ExoPTF) A Strategy for the Detection and Characterization of Exoplanets Jonathan Lunine, Chairman
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Presentation and discussion tonight (Tues.), 7:15 PM, Ballroom G • • • • • • ’ • !
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• ZAMS habitable zone
Kasting et al., Icarus (1993) • The habitable zone is considered to be reasonably wide as a consequence
of stabilizing feedbacks between atmospheric CO2 and climate • Bad things happen, though, to planets around stars much different from the Sun --F and A stars: high stellar UV fluxes, short main sequence lifetimes --Late K and M stars: tidal locking, stellar flares, initial volatile inventories?
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The Gliese 581 planetary system compared to our own
Tentative conclusions for the Gliese 581 system*
• Gliese 581c (> 5.1 M") is probably not habitable – Wikkipedia is wrong! – Stellar flux is 30% higher than that for Venus
• Gliese 581d (>8.3 M") could conceivably be habitable, but it is probably an ice giant – Near the (poorly determined) outer edge of the HZ • But, the good news is that searching for habitable planets around M stars using ground-based RV looks doable!
Finding M-star planets using transits • Presentation to the ExoPTF by Dave Charboneau (February, 2007) • Relative radii: Sun 1 Jupiter 0.1 M star 0.1-0.3 Earth 0.01 • Thus, the light curve for Earth around a late M star is • about as deep (~1%) as for Jupiter around a G star • The HZ around an M star is also close in ! transits are reasonably probable Possible problems for planets around M stars
• Tidal locking – But this can probably be overcome by atmospheric and oceanic heat transport • Lack of magnetic field ! atmospheres may be removed by flares and sputtering (H. Lammer et al., Astrobiol., 2007) • Initial deficiency in volatiles due to smaller orbits, hotter accretion environment, more energetic collisions (J. Lissauer, Ap. J., 2007) • ’ •
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• • ’ … Astrometric method
• Calculated motion of the Sun from 1960 to 2025, as viewed from a distance of 10 pc, or about 32 light years • Scale is in arcseconds • You get the actual mass of the planet because the plane of the planet’s orbit can be determined • Can do astrometry from the ground, but the best place to do it is in space $ ! http://planetquest.jpl.nasa.gov/Navigator/ material/sim_material.cfm SIM – Space Interferometry Mission
• Narrow-angle astrometry: 0.6 $as precision on bright targets* • Could be used to identify Earth-mass (or slightly larger) planets around a significant number of nearby stars • Much of the required development work has already been done
SIM target space Earth analogue survey: 129 nearby stars
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• ! Secondary eclipse spectroscopy
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http://www.nasa.gov/mission_pages/spitzer/news/070221/index.html • What we would really like to do is to obtain spectra of terrestrial planets
• This requires better space telescopes than are currently available…
Visible or thermal-IR?
• Contrast ratio: 1010 in the visible 7 10 in the thermal-IR • Resolution: % & '/D • Required aperture: ~8 m* in the visible 80 m in the IR
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• This idea has now evolved into a free-flying interferometer, similar to ESA’s proposed (but now postponed) Darwin mission • Advantages: good contrast ratio, excellent spectroscopic biomarkers • Disadvantages: needs cooled, multiple spacecraft
• It may be easier, however, to do TPF in the visible, using a single telescope and spacecraft • Advantages: single spacecraft and telescope • Disadvantages: high contrast ratio between planet and star
Mask
8 m
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Ref: O. Guyon, A&A 404, 379 (2003)
• Occulter • ~50,000 km • Telescope Diagram from homepage of Webster Cash, Univ. of Colorado “ ” Visible Spectrum of Earth
Integrated light of Earth, reflected from dark side of moon; Rayleigh, chlorophyll, O2, O3, H2O. Ref.: Woolf, Smith, Traub, & Jucks, ApJ 2002; also Arnold et al. 2002
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All available at: http://www.geosc.psu.edu/~kasting/PersonalPage/Kasting.htm