Havard Center for Astrophysics

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

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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

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(200

9)

Super-Earths:vs.Super-Neptunes

(Sasselov 2008)

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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