[meteorite-list] Herschel Telescope Detects Water on Dwarf Planet Ceres

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?release=2014-020  

Herschel Telescope Detects Water on Dwarf Planet
Jet Propulsion Laboratory
January 22, 2014

Scientists using the Herschel space observatory have made the first
definitive detection of water vapor on the largest and roundest object
in the asteroid belt, Ceres.

Plumes of water vapor are thought to shoot up periodically from Ceres
when portions of its icy surface warm slightly. Ceres is classified as a
dwarf planet, a solar system body bigger than an asteroid and smaller
than a planet.

Herschel is a European Space Agency (ESA) mission with important NASA
contributions.

"This is the first time water vapor has been unequivocally detected on
Ceres or any other object in the asteroid belt and provides proof that
Ceres has an icy surface and an atmosphere," said Michael Kuppers of ESA
in Spain, lead author of a paper in the journal Nature.

The results come at the right time for NASA's Dawn mission, which is on
its way to Ceres now after spending more than a year orbiting the large
asteroid Vesta. Dawn is scheduled to arrive at Ceres in the spring of
2015, where it will take the closest look ever at its surface.

"We've got a spacecraft on the way to Ceres, so we don't have to wait
long before getting more context on this intriguing result, right from
the source itself," said Carol Raymond, the deputy principal
investigator for Dawn at NASA's Jet Propulsion Laboratory in Pasadena,
Calif. "Dawn will map the geology and chemistry of the surface in high
resolution, revealing the processes that drive the outgassing activity."

For the last century, Ceres was known as the largest asteroid in our
solar system. But in 2006, the International Astronomical Union, the
governing organization responsible for naming planetary objects,
reclassified Ceres as a dwarf planet because of its large size. It is
roughly 590 miles (950 kilometers) in diameter. When it first was
spotted in 1801, astronomers thought it was a planet orbiting between
Mars and Jupiter. Later, other cosmic bodies with similar orbits were
found, marking the discovery of our solar system's main belt of asteroids.

Scientists believe Ceres contains rock in its interior with a thick
mantle of ice that, if melted, would amount to more fresh water than is
present on all of Earth. The materials making up Ceres likely date from
the first few million years of our solar system's existence and
accumulated before the planets formed.

Until now, ice had been theorized to exist on Ceres but had not been
detected conclusively. It took Herschel's far-infrared vision to see,
finally, a clear spectral signature of the water vapor. But Herschel did
not see water vapor every time it looked. While the telescope spied
water vapor four different times, on one occasion there was no signature.

Here is what scientists think is happening: when Ceres swings through
the part of its orbit that is closer to the sun, a portion of its icy
surface becomes warm enough to cause water vapor to escape in plumes at
a rate of about 6 kilograms (13 pounds) per second. When Ceres is in the
colder part of its orbit, no water escapes.

The strength of the signal also varied over hours, weeks and months,
because of the water vapor plumes rotating in and out of Herschel's
views as the object spun on its axis. This enabled the scientists to
localize the source of water to two darker spots on the surface of
Ceres, previously seen by NASA's Hubble Space Telescope and ground-based
telescopes. The dark spots might be more likely to outgas because dark
material warms faster than light material. When the Dawn spacecraft
arrives at Ceres, it will be able to investigate these features.

The results are somewhat unexpected because comets, the icier cousins of
asteroids, are known typically to sprout jets and plumes, while objects
in the asteroid belt are not.

"The lines are becoming more and more blurred between comets and
asteroids," said Seungwon Lee of JPL, who helped with the water vapor
models along with Paul von Allmen, also of JPL. "We knew before about
main belt asteroids that show comet-like activity, but this is the first
detection of water vapor in an asteroid-like object."

The research is part of the Measurements of 11 Asteroids and Comets
Using Herschel (MACH-11) program, which used Herschel to look at small
bodies that have been or will be visited by spacecraft, including the
targets of NASA's previous Deep Impact mission and upcoming Origins
Spectral Interpretation Resource Identification Security Regolith
Explorer (OSIRIS-Rex). Laurence O' Rourke of the European Space Agency
is the principal investigator of the MACH-11 program.

Herschel is a European Space Agency mission, with science instruments
provided by consortia of European institutes and with important
participation by NASA. While the observatory stopped making science
observations in April 2013, after running out of liquid coolant, as
expected, scientists continue to analyze its data. NASA's Herschel
Project Office is based at JPL. JPL contributed mission-enabling
technology for two of Herschel's three science instruments. The NASA
Herschel Science Center, part of the Infrared Processing and Analysis
Center at the California Institute of Technology in Pasadena, supports
the U.S. astronomical community.

Dawn's mission is managed by JPL for NASA's Science Mission Directorate
in Washington. Dawn is a project of the directorate's Discovery Program,
managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA
is responsible for overall Dawn mission science. Orbital Sciences Corp.
in Dulles, Va., designed and built the spacecraft. The German Aerospace
Center, the Max Planck Institute for Solar System Research, the Italian
Space Agency and the Italian National Astrophysical Institute are
international partners on the mission team. Caltech manages JPL for NASA.

More information about Herschel is online at:
http://www.esa.int/SPECIALS/herschel. More information about NASA's role
in Herschel is available at: http://www.nasa.gov/herschel. For more
information about NASA's Dawn mission, visit: http://www.nasa.gov/dawn.

Whitney Clavin 818-648-9734
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin at jpl.nasa.gov

J.D. Harrington 202-358-5241
Headquarters, Washington
j.d.harrington at nasa.gov

2014-020