IEEE Spectrum March, 2007 - 42

Planet Hunters
Wanted
some spare processor
cycles would be nice, too
By Mark andersOn

weBsights

As of this past december,
there were 209 planets
known to be orbiting stars
outside the solar system-209 more than were
known just two decades
ago. And while the rate of
extrasolar planet discoveries by professional astronomers is impressive (27 new
planets were discovered in 2006
alone), some researchers think
the catalog of new worlds could
swell even faster. the discoveries could mount not by building
new planet-finding telescopes
or satellites, but by marshalling
an army of amateur astronomers
and enthusiasts along with their
personal computers.
the researchers believe
that many extrasolar planets
have already been unwittingly
detected through telescopes but
that they are hidden because of
the complexity of teasing out the
signal of the planet's existence
from a mountain of astronomical data. Now two free programs
are being developed that will let
anyone hunt through the data for
our cosmic neighbors.
the reason it's so hard to
identify planets is that, unlike
stars and some nebulae, planets don't give off their own light.
While satellites are in the works
to directly detect the dim light
that gets reflected from planets orbiting stars, nearly all the
known extrasolar planets have
been uncovered using the same
method astronomers typically

NIcK doLdINg/gEtty IMAgES

www.spectrum.ieee.org

use to discover black holes. they
look not for the object directly but
for its invisible gravitational tug
on the luminous star nearby.
this tug causes the star to
wobble slightly back and forth
as seen from Earth, or more formally, the star's "radial velocity"
accelerates and decelerates. the
wobble can be detected because
the frequency of the light from
the star will be altered by the
doppler effect. that is, when
the star's wobble moves the star
closer to us, its light is shifted
slightly toward the blue end of
the spectrum, and when the
wobble pulls the star away from
us, its light is shifted toward the
red end of the spectrum.
using this effect, for example,
an alien astronomer observing
our sun would notice that the sun
wobbles back and forth every
23.8 years, and some number
crunching would reveal that period
to be the signature of a large
gas giant orbiting the sun every
11.9 years-in this case, Jupiter.
Not surprisingly, finding tiny
planet-induced doppler shifts of a
star's spectrum is a very delicate
undertaking. And when there are
three or four large planets like
Jupiter and Saturn in orbit around
a star, the complex superposition
of wobbles that the invisible companions produce are even more
challenging to decode.
Astronomer greg Laughlin,
at the university of california,
Santa cruz, wants to make anyone willing to learn a few basic
March 2007 | IEEE Spectrum | NA

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http://www.spectrum.ieee.org

Table of Contents for the Digital Edition of IEEE Spectrum March, 2007

IEEE Spectrum March, 2007 - Cover1
IEEE Spectrum March, 2007 - Cover2
IEEE Spectrum March, 2007 - 1
IEEE Spectrum March, 2007 - 2
IEEE Spectrum March, 2007 - 3
IEEE Spectrum March, 2007 - 4
IEEE Spectrum March, 2007 - 5
IEEE Spectrum March, 2007 - 6
IEEE Spectrum March, 2007 - 7
IEEE Spectrum March, 2007 - 8
IEEE Spectrum March, 2007 - 9
IEEE Spectrum March, 2007 - 10
IEEE Spectrum March, 2007 - 11
IEEE Spectrum March, 2007 - 12
IEEE Spectrum March, 2007 - 13
IEEE Spectrum March, 2007 - 14
IEEE Spectrum March, 2007 - 15
IEEE Spectrum March, 2007 - 16
IEEE Spectrum March, 2007 - 17
IEEE Spectrum March, 2007 - 18
IEEE Spectrum March, 2007 - 19
IEEE Spectrum March, 2007 - 20
IEEE Spectrum March, 2007 - 21
IEEE Spectrum March, 2007 - 22
IEEE Spectrum March, 2007 - 23
IEEE Spectrum March, 2007 - 24
IEEE Spectrum March, 2007 - 25
IEEE Spectrum March, 2007 - 26
IEEE Spectrum March, 2007 - 27
IEEE Spectrum March, 2007 - 28
IEEE Spectrum March, 2007 - 29
IEEE Spectrum March, 2007 - 30
IEEE Spectrum March, 2007 - 31
IEEE Spectrum March, 2007 - 32
IEEE Spectrum March, 2007 - 33
IEEE Spectrum March, 2007 - 34
IEEE Spectrum March, 2007 - 35
IEEE Spectrum March, 2007 - 36
IEEE Spectrum March, 2007 - 37
IEEE Spectrum March, 2007 - 38
IEEE Spectrum March, 2007 - 39
IEEE Spectrum March, 2007 - 40
IEEE Spectrum March, 2007 - 41
IEEE Spectrum March, 2007 - 42
IEEE Spectrum March, 2007 - 43
IEEE Spectrum March, 2007 - 44
IEEE Spectrum March, 2007 - 45
IEEE Spectrum March, 2007 - 46
IEEE Spectrum March, 2007 - 47
IEEE Spectrum March, 2007 - 48
IEEE Spectrum March, 2007 - Cover3
IEEE Spectrum March, 2007 - Cover4
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