Searching for Life Beyond The Solar System

Dr. Victoria Meadows NASA Astrobiology Institute

Spitzer Science Center/California Institute of Technology

Life Beyond Our Solar System

“There are countless suns and countless earths all rotating around their suns in exactly the same way as the seven planets of our system. We see only the suns because they are the largest bodies and are luminous, but their planets remain invisible to us because they are smaller and non-luminous. The countless worlds in the universe are no worse and no less inhabited than our Earth.”

- GIORDANO BRUNO (1584)

What Is Astrobiology?What Is Astrobiology?

• Astrobiology is the scientific study of life in the universe, its past, present and future.

• Astrobiology seeks to answer three questions:– How does life begin and develop?– Does life exist elsewhere in the universe?– What is life’s future on Earth and beyond?

• Astrobiology is an interdisciplinary science– combines biology, chemistry, geology, astronomy,

planetary science, paleontology, oceanography, physics, and mathematics to answer these questions.

• Astrobiology is the scientific study of life in the universe, its past, present and future.

• Astrobiology seeks to answer three questions:– How does life begin and develop?– Does life exist elsewhere in the universe?– What is life’s future on Earth and beyond?

• Astrobiology is an interdisciplinary science– combines biology, chemistry, geology, astronomy,

planetary science, paleontology, oceanography, physics, and mathematics to answer these questions.

Where would we start the search for life outside our Solar System?

First, find a habitable world

What Is a Habitable World?

A world that can maintain liquid water on its surface

Challenges: Separating Planet and Star

In the visible, they don’t give off their own light

They are VERY far away, which makes them very faint

They are lost in the glare of their star

Learning About the Planet

• We will not be able to see details on it

• Everything we learn will be “disk-averaged”.

• The signs of life must be a global and on the surface

• Our interpretation is only as good as how deep we can see!

Learning About Distant Worlds

Radio

Infrared

Visible

Ultra-Violet X-Ray

Gamma Rays

Greenhouse Warming

Teffective Tsurface Greenhouse

Venus -43C 470C 513C

Earth -17C 15C 32C

Mars -55C -50C 5C

After Table 9.1, Bennet, Shostak, Jakosky, 2003

Δ 37 C Δ 520 C

A planet’s greenhouse effect is at least as important in determining that planet’s surface temperature as is its distance from the star!

So Many Planets…

• 211 planets known beyond our Solar System!

• But there’s ONE problem…

Too Big!

• These planets are mostly “giant planets”

• Small, rocky, Earth-like terrestrial planets around good parent stars are still very difficult to find.– A handful of M < 10 Earth masses known

– Recent discovery of Gl 581c, > 5.1 Mearth

R. Hasler

How can we tell if a planet is inhabited?

Hi!

DEAFENING

SILENCE!

Without direct contact with an alien civilization, or travelling to the nearest solar system, our best chance for finding life in the Universe is to look for global changes in the atmosphere and surface of a terrestrial planet.

Signs of Life

• Astronomical Biosignatures are global-scale photometric, spectral or temporal features indicative of life.

• Earth shows us that life can provide global-scale modification of:– A planet’s atmosphere

– A planet’s surface

– A planet’s appearance

over time

• Biosignatures must always be identified in the context of the planetary environment– e.g. Earth methane and Titan methane

CH4

O3

Signs of Life: Atmosphere

Ref

lect

ivit

y

Signs of Life: Surface

Signs of Life: Time

NOAA-CMDL

A Diversity of Worlds

Star-Planet Distance

Cir

cula

rit

y

A Diversity of Worlds in Space…

Water Content WetDry

…and Time

Archean

Modern

Proterozoic

Earths Around Other Stars

CO2

CH3Cl

CH4

O3

+

N2O

H2O

EarthAD Leo planet

Active M Star Planets

Earth-like planets around M stars with similar surface fluxes can produce simultaneous strong signatures of O2 or O3 and CH4, CH3Cl or N2O.

N2O

Early Earth-like Planets

Modern Earth

355ppm CO2

Proterozoic

0.1PAL O2

100ppm CH4

15% decrease in ozone

column depth

Archean

N2 99.8%2000ppm CO2

1000ppm CH4

100ppm H2

High CO2 Early Earth-like Planet

High CO2 Early Earth-like Planet

The Coevolution of Photosynthesis with the Atmosphere On Extrasolar Worlds

Why Are Plants Green?

Terrestrial Planet Finders

Direct detection of planetsLaunch… ?

Terrestrial Planet Finder NASA

Darwin ESA

http://vpl.ipac.caltech.edu

http://planetquest.jpl.nasa.gov