IEEE Spectrum March, 2007 - 44

radial velocity data. After creating the best-fit planetary system,
a user can then post the results
to Systemic's online "back end"
and compare them with those
of other aspiring planet hunters
around the world.
For example, the 313 data points
for the known planet-bearing star
55 cancri A reveal that the star is
experiencing wobbles that speed
up or slow down its radial velocity by as much as 100 meters per
second. using these data, since
1997 professional astronomers
have determined the presence of
four planets orbiting 55 cancri A.
With Systemic, a skilled amateur
user can regenerate something
approaching this decade of professional results in less than half
an hour. What's more, of the 82
proposed 55 cancri A planetary
systems that users have already
uploaded to http://oklo.org, some
of the tightest fits to the data feature five or six planets, not four.
clearly, 55 cancri A hasn't yielded
up all its planetary secrets yet.
the opportunities for amateur
science, says Jaymie Matthews
of the university of british
columbia, in Vancouver, are rife
with a program like Systemic.
"you never know, sometimes
that flash of inspiration comes
from an unexpected direction,"
he says. "We're fortunate in
astronomy in that without an
accelerator in your basement
or a 10-meter telescope in your
backyard, you can still potentially make contributions to the
cutting edge of science."
hOwever, the wOBBle

method works best for detecting
Jupiter-type planets, which are
massive enough to really tug on
their stars. the best chance for
finding Earth-sized planets (and
hence possible homes for E.t.)
may rely instead on a much more
difficult technique at the heart
of another online project called
planetQuest (http://planetquest.
org). the technique, known as
the photometric transit method,
involves closely monitoring the
brightness of a star and looking
www.spectrum.ieee.org

for slight dips in its luminosity
as a planet passes in front of it,
blocking some of its light.
No planet has yet been discovered using this method, however. this is, in part, because a
planet's transit across a star's
face, as seen from Earth, might
last only a fraction of a day and
can occur only once during the
planet's orbit, the length of which,
of course, could easily be measured in years.
As a result, digging out these
momentary dips in luminosity
from archived measurements of
stellar brightness is a huge exercise in data mining that, according
to Laurence doyle, an astrophysicist at the SEtI Institute,
in Mountain View, calif., is best
tackled by distributed computing. drawing from more than
two years of dedicated nightly
observations of eight fields of
stars, planetQuest will comb
through the data for periodic dips
in stellar luminosity. Each field of
stars is one degree across in the
constellations cassiopeia and
Sagittarius, with each image containing 16 million pixels and tens
of thousands of stars.
Naturally, though, a star's
brig htne s s could incr ease
and decrease for many reasons. perhaps a wisp of a cloud
momentarily passed overhead,
or the telescope's mirror warped
slightly due to a change in temperature. So the challenge the
planetQuest team faces is to
find those rare cases when the
dimming and brightening happen in a periodic way that can be
explained in terms of a possible
planetary transit.
Factoring in the numerous
possible planetar y transits
across both single- and double-star systems, planetQuest
requires an estimated three cpuyears to analyze the light from a
single star. So planetQuest will
divvy up the problem and let
many hundreds or thousands of
computers tackle it. closely modeled on the SEtI@home approach,
the project that uses Internetconnected computers in the
March 2007 | IEEE Spectrum | NA

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http://www.oklo.org http://planetquest http://www.spectrum.ieee.org
Table of Contents for the Digital Edition of IEEE Spectrum March, 2007
