Astrobiology in the Context of a Research University

Dimitar D. Sasselov

Center for Planetary Astrophysics &Department of Astronomy Harvard University

One of Humankind’s Biggest Questions:

What is the path from Stars to Life ?

• One of the last remaining unresolved questions

• It has become tractable by modern science• Major emerging discipline - one could lead !

The “Essence” of Life

• Resolving the “Chicken-&-Egg” problem of nucleic acids vs. proteins - too much complexity ?

• Solution: RNA-catalyzed RNA replication !

The “Essence” of Life

• Find how Darwinian behavior can emerge from chemistry

• Develop synthetic self-replicating molecules

• Membranes & vesicles - cell division before cells !

RNA (red) adsorbed into clay, inside a vesicle (green) - Szostak lab (2004).

The Ultimate Leap: Chemistry to Life

• Prebiotic chemistry: find a plausible route to “self-replicators”;

• Prebiotic chemistry: on mineral surfaces, inside atmospheric particles, and ice-eutectic reactions;

• Prebiotic chemistry: on the young Earth, other planets and in space ?

Co-evolution of Planets and Life

• Life as a planetary phenomenon:

constraining the chemical pathways that led to life.

• Unearthing the evidence - how did it all begun on Earth ?

• The next big question - was Mars alive ?

A fossil cyanobacteriumin circa 1.5 Gyr old sedimentary rocks - (A. Knoll).

distinct layers of sedimentary rocks

(A. Knoll,Sept. 2004)

Mars,Endurance Crater

The Universe is the “stage”…

• Planets - cradles for life in a hostile Universe

• Search & exploration: by end of decade - know planets like Earth

• Formation & stability of planetary systems

Artist concept of a hot Jupiter

The Planetary Perspective

• The initial condition: chemical makeup & isotopes;

• Precise timeline of early events.

A pre-solar SiC grain from theMurchison meteorite.

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2 microns

The Planetary Perspective

• Precise timeline of early events.

Jacobsen (2003)

Planets Orbiting Other Stars

Number of planets discovered around stars like our Sun:

154 planets 14 multiple planet systems

Transits: A New Method for Planet Discovery

Venus in Front of the Sun

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Transit Measurements

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Evidence for Planet OGLE-TR-56b

Light Dimming

Doppler Shift

Konacki, Torres, Jha,

Sasselov, 2003, Nature

Mass-Radius diagram:

Kon

acki

, Tor

res,

Sas

selo

v, J

ha (

2005

)

All knowntransitingextra-solarplanets

HD 209458b: a Hot Jupiter

The Next Step:Find Planets like Earth

Lynnette Cook

KEPLER: Search for Earth Twins

GOAL: discover ~12 Earths in habitable zones; also - thousands of giant planets like Jupiter.

NASA Mission - launch in 2007

Transit Search: ~100,000 stars

Can detect planets like our Earth

Why in a University ?

• A major emerging discipline.

• Education: a bridge b/n life & physical sciences– Undergraduate: e.g. Harvard Melton/Gross committee– Graduate: specialized courses; workshops– Public outreach: immense potential (lecture series, etc)

Special thanks to team members:

S. Jacobsen, J. Szostak, A. Knoll, S. Martin, M. Shair

Additional Slides

The Other Known Transiting Extrasolar Planet

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

Model: Seager & Sasselov 2000

Detection: Charbonneau et al 2002

NASA’s Terrestrial Planet Finder

• Find and characterize Earth-like planets

• Reduce the glare of the parent star by one million to one billion

• Launch date 2015

• Observe stars within 50 light years

Alcatel Space Industries

At Harvard NOW:

NEXT:

The Ultimate Leap: Chemistry to Life

RNA (r