The
Search for More Earths
Summary (Jul 16,
2004): When astronomers first realized that the stars in the
sky were like our Sun, only more distant, they wondered if
those stars had planets too. And if they have planets, is
there life? Intelligent life? There's an answer - yes or no -
but we don't know it yet. NASA and the European Space Agency
are working on a series of space and ground-based
observatories that may help get an answer soon. In just a
decade, you could gaze into the night sky, locate a star, and
know that there's life there. Life could be everywhere.
Display Options: 
The Search for More Earths
by Fraser Cain,
Universe
Today
 |
Scene from a moon orbiting the
extra-solar planet in orbit around the star HD70642.
Credit:David A. Hardy, astroart.org (c)
pparc.ac.uk |
Until a decade
ago, astronomers weren't even sure there were any planets
outside the Solar System. You'd be hard-pressed to find anyone
who believed we had the only planets in the entire Universe,
but we still didn't have any direct evidence they existed.
That all changed in October 5, 1995 when Michel Mayor and
Didier Queloz announced they had discovered a planet half the
mass of Jupiter orbiting furiously around a star called 51
Pegasi. The discoveries came fast; at last count, there are
122 confirmed extrasolar planets.
But these extrasolar
systems generally look nothing like our own Solar System. Many
contain massive planets which orbit extremely close to their
parent star; no chance for life there. Planets roughly the
size and orbit of Jupiter have been uncovered, but it's
impossible for the current technology to see anything the size
of our own Earth.
Fortunately, there's a
series
of ground and space-based observatories in the works that
should be capable of detecting Earth-sized planets around
other stars. NASA and the ESA are working towards the goal of
being able to directly photograph these planets and measure
the composition of their atmospheres. Find large amounts of
oxygen, and you've found life.
Corot
- 2006
The European Space Agency will be the first
off the mark in the hunt for rocky planets with the launch of
Corot in
2006. It'll carefully monitor the brightness of stars,
watching for a slight dimming that happens in regular
intervals. These dimmings are called "transits", and happen
when a planet passes in between the Earth and a distant star.
The concept of a "transit" should be fresh in your mind -
Venus performed one recently on June 8, 2004. Corot will be
sensitive enough to detect rocky planets as small as 10 times
the size of the Earth.
 |
SIM, scheduled for launch in 2009,
will determine the positions and distances of stars
several hundred times more accurately than any previous
program.
Credit: NASA / JPL |
A
follow on mission, Eddington, was originally scheduled for
launch in 2007, would have been able to spot planets half the
size of the Earth. But it was recently canceled,
unfortunately.
Kepler
- 2007
The first space observatory designed to
find Earth-sized planets in orbit around other stars will be
Kepler, named after the German astronomer who devised the laws
of planetary motion. It's scheduled to launch in 2007, and
will also use the transit method to detect planets.
Kepler has an extremely sensitive photometer hooked up
to its one-metre telescope. It'll monitor the brightness of
hundreds of thousands of stars in a chunk of sky about the
same size as your outstretched hand, and watch for that
telltale periodic "dimming".
Over the course of its
four year mission, Kepler should discover plenty of objects
orbiting other stars, and its photometer is just sensitive
enough that it should notice an Earth-sized planet as it
crosses in front of a star for a few hours.
Space
Interferometry Mission -
2009
Next up will be the Space Interferometry
Mission, due for launch in 2009. Once in space, the SIM will
take up a position in orbit that trails the Earth as it goes
around the Sun, slowly drifting further and further away -
this'll give it a good, stable view of the heavens, without
having the Earth around to block the view.
The
observatory is designed to measure the distance to stars with
incredible precision. It's so precise, that it should be able
to spot a star being moved through the gravitational
interaction with its planets. For example, if you looked at
the position of our own Sun from a distant point, it would
look like it's wobbling around thanks to the gravity of
Jupiter, Saturn, and even the Earth. SIM will be able to
detect a star's interactions with planets down to the size of
a few times the mass of the Earth. That's precise.
Terrestrial
Planet Finder -
2012-2015
 |
The Terestrial Planet Finder will
search for Earth-like planets orbiting 250 of the
closest stars.
Credit:
NASA |
Unlike the previous
missions, which will detect Earth-sized planets indirectly,
the Terrestrial Planet Finder (TPF) will "see" them. It's
scheduled for launch in 2012 and will nullify the light from
distant stars by a factor of 100,000 times, revealing their
planets. The final design is still in the works, but it could
end up being a group of spacecraft flying in close formation,
merging their light together to form a much larger virtual
space telescope.
The TPF will pick up where SIM leaves
off, surveying the habitable zone of stars 50 light years away
from the Earth. Not only will it be able to see Earth-sized
planets in these zones, it'll be able to analyze the
composition of their atmospheres. Here's the key: the TPF will
be able to spot the presence of oxygen, water vapour, methane
and carbon dioxide in Earth-sized planets in the habitable
zone of other stars. If could find the fingerprint for life in
the atmospheres of these planets.
Find life on other
planets, and you can assume that it's probably common
throughout our Milky Way galaxy, and maybe even the entire
Universe.
Darwin
- 2014
Shortly after the TPF gets to work, the
European Space Agency is planning to launch Darwin; a flotilla
of 8 spacecraft working together to find Earth-sized planets
and search for the chemical signatures of life. Darwin will be
the most powerful space-based observatory, providing images
10-times more detailed than even the James Webb Space
Telescope (due for launch 2009).
Stars are billions of
times brighter than the planets that orbit them, so Darwin
will solve this problem by observing in the infrared spectrum,
where this difference is much smaller. It'll also be capable
of canceling out starlight to reveal the much dimmer
planets.
Darwin is similar enough to the Terrestrial
Planet Finder, that the two agencies are considering combining
their designs into a single mission funded by both
groups.
Maybe we aren't alone after
all.In just a decade, and less than 20 years
after the discovery of the first planets orbiting other stars,
astronomers should be able to supply us with an answer to one
of the most fundamental questions humans have asked
themselves... are we alone? If the Terrestrial Planet Finder
hasn't turned up evidence of life yet, then the answer will
still be, "not yet". But there's a chance that in 10 years,
you'll be reading news that that life has been discovered
orbiting another star.
But that won't be the end of it.
The scientists will press on, with new equipment,
observatories and techniques to search even deeper into space.
And the philosophers and theologians will get to work
considering our place in a very crowded Universe.
Timelines
1990
- Hubble Space Telescope
launches aboard Space Shuttle Discovery, as
Earth
Orbiting Observatory1994
- Hubble Space
Telescope finds evidence of black hole in the center of
M87
- Hubble
Key
Project begins studying Cepheid variable stars to better
define Hubble Constant, and the size of the
universe
1996
- Sidney van den Bergh and
Gustav Tammann debate Hubble Constant and the scale of the
universe
1998
- Jim Peebles and Michael
Turner debate nature of universe and whether cosmology is
solved
1999
- John Cowan confirms age
estimates of globular clusters and universe by dating
metal-poor stars
- Wendy Freedman and Allan Sandage debate
Hubble
Constant and the
scale of
universe2001
-
Hubble
Space Telescope detects an atmosphere around an extrasolar
planet
2002
- Chandra X-ray Observatory finds
evidence for new matter in "
quark
stars", matter so dense it exceeds terrestrial nuclear
material with 1.2 million degree
temperatures
2003
- Final mission in NASA
Great Observatory series, the infrared observatory, or Spitzer
Space Telescope, finds evidence for organic molecules in
intergalactic regions
-
Microwave
measurements precisely date the Big Bang at 13.7 billion
years ago, with a remarkable 1% error
prediction
2006
- French
COROT mission
will look at 50,000 to 60,000 stars and should find a few
dozen terrestrial planets and several hundred close-in
gas-giant planets during a two- to three-year
mission
2007
-
Kepler, Extrasolar
Terrestrial Planet Detection Mission, designed to look for
transiting or earth-size planets that eclipse their parent
stars [survey 100,000 stars]. Scientists expect to find
thousands of planets, and perhaps 50 Earth-like
candidates.
- Likely de-orbit for Hubble
Space Telescope [date announced is highly fluid but assumes no
planned shuttle visits from
NASA]
2009
- Planned launch for
NASA-ESA Next Generation Space Telescope, or NGST [
James Webb Space
Telescope], a near-infrared telescope that will succeed
the Hubble Space Telescope.
- Planned launch for Space
Interferometery Mission
(SIM)
2012-2015
- Planned launch
for TPF and Darwin missions
Related Web Pages
The University of California Planet Search
Project Astrobiology
Magazine New Planets Transit
Search Extrasolar
Planets Encyclopedia
Planet Quest
(JPL)
Kepler
Mission Darwin Mission Space Interferometry
Mission Three
Tough QuestionsFrequent
Wet Earths? Habitability:
Betting on 37 Gem Discovering
New Worlds Star
Bright: Part INote:
New Planets
Display Options: Friday, July 16, 2004
