This story was updated at 1:45 p.m.
EDT.
A recently spied planet orbits so close to its star that a new year comes every
10 hours.
Called
SWEEPS-10, the planet [image]
belongs to a newfound class of zippy exoplanets called ultra-short-period planets (USPPs) that have orbits of less than a day.
The Hubble Space Telescope
recently spotted five USPPs, all about the size of
Jupiter, in a crowded star field [image]
near the galactic
bulge of our Milky Way galaxy
as part of an exoplanet survey called the Sagittarius
Window Eclipsing Extrasolar Planet Search (SWEEPS). A
total of 16 planet candidates were found, all with relatively short orbital
periods.
"These
are the farthest planets detected so far around some of the faintest stars,"
study leader Kailash Sahu
of the Space Telescope Science Institute (STScI) in
Maryland told reporters at a NASA press conference.
Extrapolated
to the entire Galaxy, the Hubble results suggest the Milky Way contains at
least 6 billion Jupiter-sized planets, researchers say.
The findings
are detailed in the Oct. 5 issue of the journal Nature.
The new
planets were discovered using the transit technique, in which researchers
calculate a planet's mass and size based on the periodic dimming of starlight
the planet creates when it passes in front of its parent star.
Previously,
the shortest known orbital period for a planet was 1.2 days and belonged to a
"hot
Jupiter," a giant gas planet that also orbited close to its star. In
our solar system, Mercury is the
closest planet to our Sun and has an
orbital period of 88 days. Earth,
located farther away, takes about 365 days to make one full orbit.
Unlike with
hot Jupiters, the stars the USPPs
orbit are small. The star that SWEEPS-10 orbits has less than half the mass of
our Sun. The stars' small sizes are
likely what allow the planets to orbit so close, the researchers say. Planets orbiting larger stars at such
close ranges would be destroyed.
"If
sun-like stars have this kind of planet close to the star, it would simply
evaporate the planet," Sahu said.
SWEEPS also
confirmed something that astronomers have long suspected: that stars rich in
heavy elements like carbon and iron are more likely to have planets.
"We
wanted to now if this holds halfway around the galaxy," said study team
member Mario Livio, also of STScI.
"We found that indeed, it does hold. If you find a star rich in heavy
elements, there's a high probability that there will be a planet around it."
Alan Boss,
a planet expert at the Carnegie Institution of Washington who was not involved
in the study, said the new findings underscore the fact that the three types of
planets found in our solar system--rocky planets, ice giants and gas giants--also
appear to be abundant in the universe at large.
"We know
that all three examples are out there, and that gives us great hope for the
future of the field," Boss said.
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