Havard Center for Astrophysics

The Search for Life in the Universe Dimitar Sasselov Department of Astronomy Harvard 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-Earths vs. Super-Neptunes (Sasselov 2008) Image: S.Cundiff

Direct Detection of Planets
Direct detection is challenging because of the technical
limits of
telescopic
observations

Direct Detection of Planets
Three planets
orbiting 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 us DIRECTLY: Planet radius, INDIRECTLY: Planet density Planet composition

The HAT Network: FLWO Mt.Hopkins & Hawaii ( Bakos et al. 2006 )

A New super-Neptune: HAT-P-11b Bakos, Noyes, Pal, Latham, Sasselov et al. (2009)

Super-Earths: vs. Super-Neptunes (Sasselov 2008) Image: S.Cundiff

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 Emission Infrared Eclipses of Hot Jupiters: Spitzer Space Telescope

New 2  m Spectrum for HD 189733b (Swain et al. 2008)

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)

New Earths Facility
Discovery 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 rate comb for astro applications and demo on mountain-top 2009 : Optimized system for 1 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 M Earth 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 different initial conditions are “driven” to a set of geochemical equilibria by global geo-cycles over geological timescales. 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 diversity of 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

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