Download How do we look for life?

EXPLORING ASTROBIOLOGY
How do we look for life?
Planet Survey
Venus and Mars at sunrise, from orbit
Image: NASA
So how do we go about looking for life beyond Earth?
The first step in the search for extraterrestrial life is to locate as many planets
and moons as we can—in our solar system and elsewhere.
EXPLORING ASTROBIOLOGY
How do we look for life?
Close to Home
Left: William Herschel,
discoverer of the planet
Uranus
Right: A telescope
made by Galileo
Gallilei, discoverer of
Jupiter’s four major
moons
In an effort that began in ancient times, the
major planets, moons, and small bodies that
orbit our star—the Sun—have been located.
EXPLORING ASTROBIOLOGY
How do we look for life?
Extrasolar Planet Search
Artist’s View of Planetary System in Globular Cluster M4
NASA and G. Bacon (STSci) – STSci-PRC03-19a
There are billions of stars out there. Of course not all stars have planets, but
many do. Between 1995 and 2004, 108 extrasolar planetary systems—
with some 123 planets—were located in our stellar neighborhood.
EXPLORING ASTROBIOLOGY
How do we look for life?
Seeing the Unseen
Artist’s View of Planet Around Star Gliese 876
NASA and G. Bacon (STSci) – STSci-PRC02-27
Finding extrasolar planets is difficult, because they are so distant and dim that
their parent star obscures them. They can only be detected indirectly, through
their effects on their star’s motion and appearance.
EXPLORING ASTROBIOLOGY
How do we look for life?
Likely Locations
High-resolution 3D Images from ESA Mars Express Orbiter
Images: ESA
The next step is to narrow the search to planets and moons in so-called
“habitable zones” where life could theoretically exist. Information about geology,
atmosphere, composition, history, and relationship to the rest of its solar system
is required to determine if a world might be hospitable to life.
EXPLORING ASTROBIOLOGY
How do we look for life?
Unsuited for Life
Some solar systems are
probably not suitable for any
kind of life. Some factors that
make a system unlikely to
harbor life are:
• stars whose temperature
and light vary in intensity.
• multiple star systems
• high energy radiation from
the star or surrounding areas
• very old, very young, very
hot, and very cool stars
Artist's Concept, Evaporating Planet HD 209458b
Image: NASA
EXPLORING ASTROBIOLOGY
How do we look for life?
Potential Homes
Image: NASA
Earth From Low Orbit
To qualify as a potential home for life as we know it, a location must have
liquid water, temperatures between -4°F (-20°C) and 266°F (130°C),
an energy source, and organic molecules.
EXPLORING ASTROBIOLOGY
How do we look for life?
Just Right
Sunrise, Nepal
For liquid water to exist, a planet needs a source of heat such as tidal forces or
heat from its sun. If the heat comes from a star, the planet has to be in a
“Goldilocks” position, just the right distance from the star to allow for liquid water.
EXPLORING ASTROBIOLOGY
How do we look for life?
Viable Energy Source
Hydrothermal Vent and Chemosynthetic Bacteria
Image: NOAA
An energy source might include sunlight for photosynthesis or chemicals for
chemosynthesis. Organic molecules could include amino acids, carbohydrates, or
methane, which can all be produced by atmospheric and geologic processes.
EXPLORING ASTROBIOLOGY
How do we look for life?
The Signature of Life
Credit: Defense Meteorological Satellite Program
Night View of Earth
A potentially hospitable planet might display detectable biosignatures, such as
visible signs of life, quantities of organic molecules, or atmospheric gases resulting
from metabolism.
EXPLORING ASTROBIOLOGY
How do we look for life?
Finding Habitable Worlds
Mariner 2
Cassini-Huygens
Artist’s Concepts
Images: NASA
Mars Exploration Rover
Since the 1960s, spacecraft like Viking, Mariner, Voyager, Galileo, Mars Global
Surveyor, the Mars Exploration Rovers, and the Cassini/Huygens Mission
have been providing detailed information about the planets in our solar system.
EXPLORING ASTROBIOLOGY
How do we look for life?
Bridging the Gap
But what about distant worlds?
Physical probes, even if we decided
to send them, couldn’t reach the
vicinity of other stars for many,
many years. Investigation of
extrasolar planets will have to be
done at a distance, with future
space telescopes like the Terrestrial
Planet Finder.
HD 209458, a planetary system 150 light years from
Earth. It would take an impossibly long time for a
probe to get there!
EXPLORING ASTROBIOLOGY
How do we look for life?
Terrestrial Planet Finder
Artist’s Concept, Terrestrial Planet Finder
Image: NASA
The Terrestrial Planet Finder space telescope mission will provide us with the
closest look we’re likely to get of extrasolar planets.
EXPLORING ASTROBIOLOGY
How do we look for life?
A Different Approach
The radio telescope at Arecibo, Puerto Rico
Goldstone Radio Telescope, California
The Search for Extraterrestrial Intelligence (SETI) is an alternative approach to the
search for life. It searches the sky not for planets and biosignatures, but for detectable
signs of intelligent life—such as radio signals and other forms of communication.
Stay tuned!