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Planets common
as stars in galaxy
By Nadia Drake
When you turn an eye to the evening sky,
there’s a good chance that many of the
stars you see have at least one planet.
Using six years of data from planet-finding surveys, an international
team of researchers concludes that,
on average, a star in the Milky Way is
accompanied by 1. 6 planets. That’s at
least 100 billion planets in all, the scientists report January 12 in Nature.
The figure might seem enormous, but
it doesn’t shock planet hunters. “I’m not
surprised by this result,” says astrophysicist Wesley Traub of NASA’s Jet Propulsion Laboratory in Pasadena, Calif.,
who was not involved in the study. “This
sounds reasonable. This sounds good.”
The scientists used data that had been
gathered from 2002 to 2007 by surveys
looking for temporary brightening in a
distant star’s light caused by the gravity of a body passing in front of it. If that
The Milky Way’s stars host, on average, at least one planet, a new analysis sug-
gests. This not-to-scale illustration depicts such stars and accompanying planets.
More like Faux-malhaut b
in 2008, astronomers claimed that the hubble space telescope
had snapped the first actual picture of an exoplanet, a pinpoint
of light found within the debris disk of a star called fomalhaut
about 25 light-years from earth (star at center, proposed planet
boxed). now, a different team of scientists spying on the presumed planet, dubbed fomalhaut b, with the spitzer space telescope suggests that the dot in the original image isn’t a planet
at all. though the team isn’t sure what the dot is, the point
of light doesn’t appear to radiate at the infrared wavelengths
where exoplanets should, a team led by markus Janson of
princeton University reports online January 24 at arXiv.org. this
isn’t the first time that fomalhaut b has stumped astronomers.
Ground-based infrared telescopes haven’t been able to see it,
and it’s tracing an unexpected path around its star. theories
proposed to explain the imaged “planet” range from a background star to light scattered by a dust cloud. — Nadia Drake
passing body is a star with one or more
planets, the system causes a predictable
boost in the distant star’s light.
Unlike other types of planet searches,
this technique, called gravitational
microlensing, works well for stars both
near Earth and far away. “If we want
to go out of our little box and see into
the infinite universe, or in the galactic
bulge, or far outside the galaxy — are
there planets even there? — then micro-
lensing is the way,” says study coauthor
Kailash Sahu, an astronomer from the
Space Telescope Science Institute in
Baltimore. And microlensing can more
easily detect small planets in orbits far
from their stars — though the new study
considered only planets circling from
half the distance of Earth to the sun out
to the equivalent of Saturn’s orbit.
