Life in the Universe

Is There Life Elsewhere in the Universe?

Elsewhere in the Solar System:

Conditions may be right for primitive life to exist on Mars (or existed in the past) and Europa. Possibly some complex molecules on Titan.

Water flow on Mars in last few years?

Life Elsewhere in the Milky Way:

To address question of whether other intelligent life exists in the Milky Way, Frank Drake formulated the Drake Equation.

The equation is usually written: N = R* • fp • ne • fl • fi • fc • L Where, N = The number of civilizations in The Milky Way Galaxy whose electromagnetic emissions are detectable.

R* =The rate of formation of stars suitable for the development of intelligent life.

fp = The fraction of those stars with planetary systems.

ne = The number of planets, per solar system, with an environment suitable for life.

fl = The fraction of suitable planets on which life actually appears.

fi = The fraction of life bearing planets on which intelligent life emerges.

fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.

L = The length of time such civilizations release detectable signals into space.

number of technological, intelligent civilizations in the Milky Way =

The Drake Equation

rate at which new stars are formed x fraction of stars having planetary systems x average number of habitable planets within those planetary systems x fraction of those habitable planets on which life arises x fraction of those life-bearing planets on which intelligence evolves x fraction of those planets with intelligent life that develop technological society x average lifetime of a technological civilization Each term is less certain than the preceding one! Only in last ten years have we addressed the second term.

Allen Telescope Array – radio SETI Optical SETI [Harvard U.] SETI League (Amateur Radio Astronomers)

More than 300 discovered.

Extrasolar Planets

Main technique: detect Doppler Shift due to wobble of star caused by unseen planet. Biased – easier to detect heavier (Jupiter-class) planets.

Second technique: detect eclipse (transit) of planet – Kepler mission.

Third technique: detect wobble in star's position in sky due to unseen planet (astrometric method).

Fourth technique: direct imaging of planet.

Fifth technique: microlensing Future missions hope to detect Terrestrial planets

Astrometric method http://planetquest.jpl.nasa.gov/science/finding_planets.cfm

506 exoplanets detected as of 6 Dec 2010 Candidates detected by radial velocity or astrometry Transiting planets microlensing imaging 397 planetary systems 471 planets 47 multiple planet systems 105 planetary systems 107 planets 7 multiple planet systems 10 planetary systems 11 planets 1 multiple planet systems 11 planetary systems 14 planets 1 multiple planet systems http://exoplanet.eu

•

Terrestrial Planet Finder (TPF) Mission

TPF Science goals – Survey stars within ~ 30 pc for planets within “habitable zone” • Looking for “Earth analogues” – Characterize any detected planets • Orbit & Spectrum • Past, current, future TPF studies – Two main designs possible – Preliminary concept studies underway for several years – Followed eventually by “Life Finder” and “Planet Imager” Image courtesy NASA/JPL 9

Detecting Terrestrial Planets Directly is HARD

Brightness differences make this a very tough problem

58.21

100 10 1 0.1

1  10 0.01

3 SunSpec 1  10 ER10pcQ 1  10 1  10 Exozody 1  10 4 5 6 7 ERtotal 1  10 1  10 1  10 1  10 10 11 8 9 1  10   1  10 14 1  10 12 13 14 0.1

0.303

Zodiacal dust planet (reflection + emission) (reflection)

wavelength [microns]

1 10 wavelen star planet+dust total 100 1  10 3 1 10 3

Non-redundant Linear Array (NRLA) [Hypertelescope]

100m

Exoplanets Seen Through an Advanced Space Telescopes

Roddier-Guyon Synthesis Imager Earth-Sun system at 10pc 12 2.7h exposure time, 5 to 15 m m

Kepler Mission – Extrasolar planet transits from space

Kepler Mission – Extrasolar planet transits from space • 700 candidate planets found 0.077 to 2.1 Jupiter masses (note, Earth = 0.003 Jupiter masses) • 8 confirmed new planets http://kepler.nasa.gov/

Is There Life Elsewhere in the Universe?

Requirements for Life:

- Elements to build cells (C, H, O most important) - Energy source to make chemical reactions happen to fuel metabolism - Liquid medium – water allows organic (C-based) molecules to dissolve and be carried into cells for metabolic reactions These conditions occurred on Earth, but it's not clear whether life was then inevitable. Also, how unique are they?

Urey-Miller Experiment (1953)

Solution of water, methane, CO 2 , ammonia, with electrical discharge => amino acids formed (building blocks of proteins, which control metabolism Later experiments produced nucleotide bases (building blocks of DNA) Yet to make cell or DNA through such experiments (although some cell like objects created from mixing amino acids and heat). Not clear how robust life is and whether it required a fortunate set of accidents.

Alternative theory:

Organic molecules, maybe even amino acids and nucleotide bases came from comets and meteoroids (a lot of Earth's water may have come from comets)