havard center for astrophysics
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The Search for Life in the Universe
Dimitar Sasselov
Department of AstronomyHarvard Origins of Life Initiative
Planets orbiting other stars:
340 planets
30 multiple planet systems
discovered as of Feb. ‘09
The Planets - our Solar System
Super-Earths
Rocky vs. Ocean
Super-Earthsvs.Super-Neptunes
(Sasselov 2008)
Imag
e: S
.Cun
diff
Direct Detection of Planets
• Direct detection is challenging because of the technicallimits oftelescopicobservations
Direct Detection of Planets
• Three planetsorbiting HR8799
(Marois et al. 2008)
Transits: A Method for Planet Discovery and Study
Please see YouTube video:
http://www.youtube.com/watch?v=Pc3M7on9gwU
Transit & eclipse of HD189733b
Heather Knutson & Dave Charbonneau (2007)
What can we learn from transiting extrasolar planets
HD 209458b: Dimming of light due to transit, observed with HST.
Brown, Charbonneau, Gilliland, Noyes, Burrows (2001)
Tells usDIRECTLY:Planet radius,
INDIRECTLY:Planet densityPlanet composition
The HAT Network: FLWO Mt.Hopkins & Hawaii
(Bakos et al. 2006)
A New super-Neptune: HAT-P-11b
Bak
os, N
oyes
, Pal
, Lat
ham
, Sas
selo
v et
al.
(200
9)
Super-Earths:vs.Super-Neptunes
(Sasselov 2008)
Imag
e: S
.Cun
diff
Model: Seager & Sasselov 2000
Detection: Charbonneau et al 2002
A study of an extrasolar planet
Spitzer Telescope data: Heather Knutson, Charbonneau et al. (2007)
Direct Detection of Thermal EmissionInfrared Eclipses of Hot Jupiters:
Spitzer Space Telescope
New 2 m Spectrum for HD 189733b
(Sw
ain
et a
l. 2
008)
NASA Kepler mission: transit search for planets
Cygnus / Lyra
(RA=19h23m, Dec=44.5d)
KEPLER: Search for Earth Twins
GOAL: to discover ~30 Earths and ~300 super-Earths in habitable zones;
NASA Mission - launch in 2009
Transit Search: ~150,000 stars
Can detect planets like our Earth
Completing the Copernican Revolution:the discovery of “New Earth”
NASA Mission - Mar. 2009
Kepler is ready to launch:
Mar. 5, 2009
Assembly at Ball Aerospace
Kepler expected yields: ~ 300 super-Earths, ~ 30 Earth analogs;
(5-10% good radii)
Kepler is ready to launch:
Mar. 5, 2009
Assembly at Ball Aerospace
Kepler expected yields: ~ 300 super-Earths, ~ 30 Earth analogs;
(5-10% good radii)
New Earths FacilityDiscovery and Surface Conditions on Earth-like planets.
• Synergy with NASA Kepler: which pinpoints exo-Earths and measures radii - we measure mass & mean density, hence composition!
HARPS-NEF spectrograph:• An ongoing Harvard/SAO/Geneva collaboration.
• Femtosecond laser astro-comb - a breakthrough in calibration
Summer 07: Ti:sapphire femtosecond laser comb
Fall 2007: characterize with astro spectrograph
2008: develop high-rep ratecomb for astro applicationsand demo on mountain-top
QuickTime and aᆰTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime and aᆰTIFF (Uncompressed) decompressor
are needed to see this picture.
2009: Optimized system for1 cm/s Doppler shift precision
Harvard/Smithsonian/MIT astro-comb project
Li et al. (2008, Nature, Apr.)
Do super-Earths have a high habitability potential ? (as compared to 1 MEarth planets)
• Yes:• many (though, not all) are expected to have same
geophysics & geochemistry as Earth;
• have stable surface conditions - • keep atmospheres easily; • have plate tectonics, hence stable geo-cycles; • stable dynamics (orbits & rotation).
Super-Earths geochemistry,e.g. the Carbonate-silicate cycle, or Sulfur cycle, etc.
Planets of differentinitial conditionsare “driven” to aset of geochemicalequilibria by global geo-cyclesover geologicaltimescales.
e.g., Halevy & Schrag (2008)
Bernard de Fontenelle“Conversations on the Plurality of Worlds” (1686)
Diversity from Uniformity
• All life on Earth shares the same system of molecules and basic processes - the unity of biochemistry.
Despite its amazing diversity!
The Tree of Life (G. Klimt)
What is the diversity of planets ?
Does it imply a diversityof possible biochemistries ?
The two main questions:
The Plurality of Worlds ?
Summary
• Our team’s ambition: - to be the place where the first Earth-like planets are discovered and studied, and to complete the Copernican Revolution.
• To begin writing the next chapter - what is life’s place in the universe?
Origins of Life: the Planetary Perspective
Life as a planetary phenomenon