From Newsgroup: sci.space.news


http://www.cfa.harvard.edu/news/2011/pr201112.html

Harvard-Smithsonian Center for Astrophysics
Press Release

Release No.: 2011-12
For Release: Friday, April 29, 2011

Student's Prediction Points the Way to Hot, Dense Super-Earth

Cambridge, MA - A planet that we thought we knew turns out to be rather
different than first suspected. Our revised view comes from new data
released today by an international team of astronomers. They made their
observations of the planet "55 Cancri e" based on calculations by
Harvard graduate student Rebekah Dawson (Harvard-Smithsonian Center for
Astrophysics), who worked with Daniel Fabrycky (now at the University of
California, Santa Cruz) to predict when the planet crosses in front of
its star as seen from Earth. Such transits give crucial information
about a planet's size and orbit.

The team found that 55 Cancri e is 60 percent larger in diameter than
Earth but eight times as massive. (A super-Earth has one to 10 times the
mass of Earth.) It's the densest solid planet known, almost as dense as
lead. Even better, the star it orbits is so close and bright that it's
visible to the naked eye in the constellation Cancer the Crab. This
makes it an excellent target for follow-up studies.

Dawson and Fabrycky's prediction played a crucial role in this new work
by motivating the search for transits. When the planet was discovered by
a Texas team in 2004, it was calculated to orbit its star every 2.8
days. Dawson and Fabrycky reanalyzed the data and found that 55 Cancri e
was much closer to its star, orbiting it in less than 18 hours. As a
result, the chances of seeing a transit were much higher.

Josh Winn of MIT and Smithsonian astronomer Matthew Holman brought the
new calculation to Jaymie Matthews (University of British Columbia), who
scheduled observations with Canada's MOST (Microvariability &
Oscillations of STars) satellite. The research team found that 55 Cancri
e transits its star every 17 hours and 41 minutes, just as Dawson and
Fabrycky predicted.

"I'm excited that by calculating the planet's true orbital period, we
were able to detect transits, which tell us so much more about it," said
Dawson.

The new technique applies to planets discovered by the radial velocity
method, in which astronomers hunt for a star that "wobbles" from the
gravitational tug of an orbiting world.

The initial confusion about the orbit of 55 Cancri e arose because of
natural gaps in the radial velocity data (because astronomers can only
observe a star at night and when it's above the horizon). Sometimes
these gaps introduce "ghost" signals that can masquerade as the planet's
true signal.

Dawson and Fabrycky chose to analyze six planetary systems where the
data seemed particularly ambiguous. In two cases they confirmed previous
results, while some remained unclear. For 55 Cancri e, a period revision
was certainly needed.

"It became very clear that the planet's actual orbital period was closer
to 18 hours," stated Dawson.

This places the planet so close to its star that it's blasted with heat,
baked to a temperature of 4,900 degrees F.

The star itself, 55 Cancri A, is a yellow star very similar to the Sun
and located 40 light-years away. It's the brightest, closest star known
to have a transiting planet.

Dawson recommends that the analysis method she developed with Fabrycky
be used on future planet discoveries. "We've cleared up some confusion
in the systems we studied, and we believe we've provided a way to avoid
future confusion," she said.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar{at}cfa.harvard.edu 

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam{at}cfa.harvard.edu 

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