June 28, 2012
J. D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov
Lynn Chandler
NASA Goddard Space Flight Center, Greenbelt, Md.
301-286-2806
lynn.chandler-1@nasa.gov
RELEASE: 12-217
HUBBLE, SWIFT DETECT FIRST-EVER CHANGES IN AN EXOPLANET ATMOSPHERE
WASHINGTON -- An international team of astronomers using data from
NASA's Hubble Space Telescope has made an unparalleled observation,
detecting significant changes in the atmosphere of a planet located
beyond our solar system.
The scientists conclude the atmospheric variations occurred in
response to a powerful eruption on the planet's host star, an event
observed by NASA's Swift satellite.
"The multiwavelength coverage by Hubble and Swift has given us an
unprecedented view of the interaction between a flare on an active
star and the atmosphere of a giant planet," said lead researcher
Alain Lecavelier des Etangs at the Paris Institute of Astrophysics
(IAP), part of the French National Scientific Research Center located
at Pierre and Marie Curie University in Paris.
The exoplanet is HD 189733b, a gas giant similar to Jupiter, but about
14 percent larger and more massive. The planet circles its star at a
distance of only 3 million miles, or about 30 times closer than
Earth's distance from the sun, and completes an orbit every 2.2 days.
Its star, named HD 189733A, is about 80 percent the size and mass of
our sun.
Astronomers classify the planet as a "hot Jupiter." Previous Hubble
observations show that the planet's deep atmosphere reaches a
temperature of about 1,900 degrees Fahrenheit (1,030 C).
HD 189733b periodically passes across, or transits, its parent star,
and these events give astronomers an opportunity to probe its
atmosphere and environment. In a previous study, a group led by
Lecavelier des Etangs used Hubble to show that hydrogen gas was
escaping from the planet's upper atmosphere. The finding made HD
189733b only the second-known "evaporating" exoplanet at the time.
The system is just 63 light-years away, so close that its star can be
seen with binoculars near the famous Dumbbell Nebula. This makes HD
189733b an ideal target for studying the processes that drive
atmospheric escape.
"Astronomers have been debating the details of atmospheric evaporation
for years, and studying HD 189733b is our best opportunity for
understanding the process," said Vincent Bourrier, a doctoral student
at IAP and a team member on the new study.
When HD 189733b transits its star, some of the star's light passes
through the planet's atmosphere. This interaction imprints
information on the composition and motion of the planet's atmosphere
into the star's light.
In April 2010, the researchers observed a single transit using
Hubble's Space Telescope Imaging Spectrograph (STIS), but they
detected no trace of the planet's atmosphere. Follow-up STIS
observations in September 2011 showed a surprising reversal, with
striking evidence that a plume of gas was streaming away from the
exoplanet.
The researchers determined that at least 1,000 tons of gas was leaving
the planet's atmosphere every second. The hydrogen atoms were racing
away at speeds greater than 300,000 mph. The findings will appear in
an upcoming issue of the journal Astronomy & Astrophysics.
Because X-rays and extreme ultraviolet starlight heat the planet's
atmosphere and likely drive its escape, the team also monitored the
star with Swift's X-ray Telescope (XRT). On Sept. 7, 2011, just eight
hours before Hubble was scheduled to observe the transit, Swift was
monitoring the star when it unleashed a powerful flare. It brightened
by 3.6 times in X-rays, a spike occurring atop emission levels that
already were greater than the sun's.
"The planet's close proximity to the star means it was struck by a
blast of X-rays tens of thousands of times stronger than the Earth
suffers even during an X-class solar flare, the strongest category,"
said co-author Peter Wheatley, a physicist at the University of
Warwick in England.
After accounting for the planet's enormous size, the team notes that
HD 189733b encountered about 3 million times as many X-rays as Earth
receives from a solar flare at the threshold of the X class.
Hubble is a project of international cooperation between NASA and the
European Space Agency. Swift is operated in collaboration with
several U.S. institutions and partners in the United Kingdom, Italy,
Germany and Japan. NASA's Goddard Space Flight Center in Greenbelt,
Md., manages both missions.
For images and video related to this finding, visit:
http://go.nasa.gov/Osbvfi
For more information about Swift, visit:
http://www.nasa.gov/swift
For more information about Hubble, visit:
http://www.nasa.gov/hubble
-end-
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