Kathleen Burton
NASA Ames Research Center, Silicon Valley, CA
(Phone: 650/604-1731, 650/604-9000) kburton@mail.arc.nasa.gov
RELEASE: 99-84AR
AMES RESEARCHERS CONFIRM NEW TECHNIQUE, EXTRA-SOLAR PLANET
NASA scientists announced today that they have used a new technique to
confirm the existence of a planet orbiting a solar-like star in the Pegasus
constellation.
Using a Vulcan photometer at the Lick Observatory, the team of researchers
from NASA’s Ames Research Center in Silicon Valley, CA, have demonstrated
that the “transit photometry” method is a viable way to detect extra-solar
planets. Transit photometry works by measuring the change in a star’s
brightness as an orbiting planet transits its face.
“We are extremely pleased about this proof of our technology,” said Mr.
William Borucki, principal investigator at Ames. “This will give the
scientific community a valuable additional tool to use in astrobiology
research.”
The planet, orbiting star HD209458, was discovered by Dr. David Charbonneau
and colleagues at the High Altitude Observatory in Boulder, CO in September
and announced in early November. The data showed that the diameter of the
planet was about 1.3 times that of Jupiter, and that it had an orbital
period of 3.52 days.
Three different research groups at Lick attempted to make observations of
the transit on November 14. However, heavy clouds precluded success until
November 21, researchers said. The November 21 observation window was
marginal because the planet’s transit across the face of its parent star
occurred during a full moon and just before the star set, resulting in a
bright sky and a rapidly changing atmospheric transparency. The Ames team’s
Vulcan photometer succeeded in observing the planet because it monitors a
huge slice of sky and measures thousands of nearby stars. Such large
amounts of data allowed the photometer equipment to correct for the poor
conditions.
Ordinarily, the photometer monitors approximately 6,000 stars each night.
Discoveries of possible planets using photometry — which reveal a planet’s
size, transit times, orbital period and the identity of its parent star —
are then forwarded to other research groups who use the “Doppler velocity”
method to obtain the mass of the star-companions. The Doppler velocity
method monitors changes in the color of a star as it moves towards or away
from the Earth.
The two planetary observation techniques are complementary, researchers
say. Used together, scientists can make inferences about an extra-solar
planet’s density and composition, providing a more complete picture.
Combining the data from the Doppler velocity and photometry observations,
for example, “it is clear that the planet’s atmosphere is inflated by its
closeness to the central star and that the planet has a density of
approximately 40% the density of water, much less dense than Saturn,”
Borucki noted.
Plans for future research using the photometry technique include extending
the current ground-based observations to a space-based platform in 2004,
the researchers said. Unlike the current ground-based methods, which must
deal with atmospheric “noise” and other problems, observations from a small
telescope in space will allow Earth-sized planets to be discovered and will
determine if the planets are in the habitable zone, Borucki said.
Ground-based observation techniques are primarily designed to locate and
observe large, Jupiter-sized gas giants orbiting other stars and are not
able to observe planets as small as the Earth.
The Ames Vulcan photometer was designed and built at NASA Ames Research
Center, with funding from the Astrobiology program. It was installed only
a few days before it was called on to monitor HD209458 to confirm the
existence of the planet.
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