Here Be Dragons

THE PLANET FINDERS
seconds, which means that it should be able to detect a nearby star's
wobble caused by the presence of a Jupiter-like planet.
PTI can also operate in a simpler mode, in which it simply looks at a
single star through the two telescopes. This technique cannot detect a
star's wobble, but it can determine whether a star's image is a "point
source" or is something more complicated, such as a binary pair. In
1997, Mike Shao's group used this method on 51 Peg, the star whose
now almost sacred "planet" was detected by Queloz and Mayor. Shao's
group claimed to find that 51 Peg was a binary system, meaning that
the "planet" was not a planet at all but a small companion star. They
wrote an abstract on this finding that got onto the Internet and then
into the pages of Science. But follow-up work showed that this result
was incorrect: 51 Peg is indeed a single star, and the planet exists after
all. When, on another occasion, we have the chance to ask Shao about
this, he laughs and says "The final word is, one of our team members
was a little bit overly enthusiastic. Once we got rid of two large sources
of error, the wiggles weren't there." Since Queloz is now a member of
Shao's team, the retraction has presumably smoothed the atmosphere
within his lab.
PTI'S main function, however, is not to detect or refute planets but
to serve as a prototype for a succession of bigger and better interferometers.
First, the Keck telescopes will be set up in differential interferometric
mode: this will involve not just the integration of the two
existing lo-meter telescopes but the construction of four small "outrigger"
telescopes that will all be optically connected. 14 The Keck
Interferometer is expected to have a precision of 10 to 30 microarcseconds
and to be capable of detecting the wobble caused by Uranus-like
planets orbiting stars as distant as 20 light-years from Earth.
The Keck telescopes will also be capable of operation in another
mode of interferometry, which should permit direct detection of the
close-in Jupiters. In this mode, two starbeams from the star of interest
are combined, and the fringe pattern measured. The measurement is
done first at visible wavelengths—a region of the spectrum in which
the star so greatly outshines the planet that the latter makes essentially
no contribution to the fringe pattern. Then the measurement is repeated
at infrared wavelengths—a region in which the planet, because
it is heated by the nearby star, does make a small but detectable contribution.
Because the planet is at a slight distance from the star, its
contribution is out of phase, and it therefore shifts the overall fringe
pattern slightly. By measuring this phase shift at many different ori-
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