[meteorite-list] NASA Instrument on Rosetta Makes Comet Atmosphere Discovery

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=4609

NASA Instrument on Rosetta Makes Comet Atmosphere Discovery
Jet Propulsion Laboratory
June 2, 2015

Data collected by NASA's Alice instrument aboard the European Space Agency's 
Rosetta spacecraft reveal that electrons close to the surface of comet 
67P/Churyumov-Gerasimenko -- not photons from the sun, as had been believed 
-- cause the rapid breakup of water and carbon dioxide molecules spewing 
from the comet's surface.

"The discovery we're reporting is quite unexpected," said Alan Stern, 
principal investigator for the Alice instrument at the Southwest Research 
Institute (SwRI) in Boulder, Colorado. "It shows us the value of going 
to comets to observe them up close, since this discovery simply could 
not have been made from Earth or Earth orbit with any existing or planned 
observatory. And, it is fundamentally transforming our knowledge of comets."

A report of the findings has been accepted for publication by the journal 
Astronomy and Astrophysics.

Analysis of the relative intensities of observed atomic emissions allowed 
the Alice science team to determine the instrument was directly observing 
the "parent" molecules of water and carbon dioxide that were being broken 
up by electrons in the immediate vicinity, about six-tenths of a mile 
(one kilometer) from the comet's nucleus. The carbon dioxide and water 
are being released from the comet's nucleus and affected by electrons 
near the nucleus.

Since last August, Rosetta has orbited within 100 miles (160 kilometers) 
of comet 67P. The Alice spectrograph on board Rosetta specializes in sensing 
the far-ultraviolet wavelength band. Alice examines light the comet is 
emitting to understand the chemistry of the comet's atmosphere, or coma. 
A spectrograph is a tool astronomers use to split light into its various 
colors. Scientists can identify the chemical composition of gases by examining 
their light spectrum. Alice is the first such far-ultraviolet spectrograph 
to operate at a comet.

Alice data indicate much of the water and carbon dioxide in the comet's 
coma originate from plumes erupting from its surface.

"It is similar to those that the Hubble Space Telescope discovered on 
Jupiter's moon Europa, with the exception that the electrons at the comet 
are produced by solar radiation, while the electrons at Europa come from 
Jupiter's magnetosphere," said Paul Feldman, an Alice co-investigator 
from the Johns Hopkins University in Baltimore, Maryland.

By looking at the emission from hydrogen and oxygen atoms broken from 
the water molecules, Alice scientists can actually trace the location 
and structure of water plumes from the surface of the comet.

The far-ultraviolet region of the spectrum allows scientists to detect 
the most abundant elements in the universe: hydrogen, oxygen, carbon and 
nitrogen. However, such measurements must be made from outside Earth's 
atmosphere, either from orbiting observatories such as the Hubble Space 
Telescope, or from planetary missions such as Rosetta. From Earth orbit, 
the atomic constituents can only be seen after their parent molecules, 
such as water and carbon dioxide, have been broken up by sunlight, hundreds 
to thousands of miles, or kilometers, away from the nucleus of the comet.

The Alice spectrograph has also studied the surface of Comet 67P/Churyumov-Gerasimenko 
and will be used in further studies of its atmosphere as the comet approaches 
the sun and its plumes become more active due to solar heating.

The comet observations will help scientists learn more about the origin 
and evolution of our solar system and the role comets may have played 
in providing Earth with water, and perhaps even life.

The Alice instrument is one of two ultraviolet spectrometers named Alice 
currently flying in space. The other is on board NASA's New Horizons spacecraft, 
which is destined to make a flyby of Pluto in July. The Alice on board 
Rosetta is probing the origin, composition and workings of comet 67P/Churyumov-Gerasimenko, 
to gather sensitive, high-resolution insights that cannot be obtained 
by either ground-based or Earth-orbiting observation. It has more than 
1,000 times the data-gathering capability of instruments flown a generation 
ago, yet it weighs less than nine pounds (four kilograms) and draws just 
four watts of power.

Other U.S. contributions aboard the Rosetta spacecraft are the Microwave 
Instrument for Rosetta Orbiter (MIRO); the Ion and Electron Sensor (IES), 
part of the Rosetta Plasma Consortium Suite; and the Double Focusing Mass 
Spectrometer (DFMS) electronics package for the Rosetta Orbiter Spectrometer 
for Ion Neutral Analysis (ROSINA). They are part of a suite of 11 total 
science instruments aboard Rosetta.

Rosetta is an ESA mission with contributions from its member states and 
NASA. Rosetta's Philae lander is provided by a consortium led by the German 
Aerospace Center in Cologne; Max Planck Institute for Solar System Research 
in Göttingen; French National Space Agency in Paris; and the Italian Space 
Agency in Rome.

NASA's Jet Propulsion Laboratory in Pasadena, California, manages the 
U.S. contributions to the Rosetta mission for the agency's Science Mission 
Directorate in Washington. JPL also built the MIRO instrument and hosts 
its principal investigator, Samuel Gulkis. The Southwest Research Institute, 
located in San Antonio and Boulder, developed Rosetta's IES and Alice 
instruments and hosts their principal investigators, James Burch (IES) 
and Alan Stern (Alice).

For more information on the U.S. instruments aboard Rosetta, visit:

http://rosetta.jpl.nasa.gov

More information about Rosetta is available at:

http://www.esa.int/rosetta


Media Contact

DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-9011
agle at jpl.nasa.gov 

Dwayne Brown
NASA Headquarters, Washington
202-358-1726
dwayne.c.brown at nasa.gov 

Joe Fohn
Southwest Research Institute, Boulder, Colo.
210-522-4630
jfohn at swri.org 

Markus Bauer
European Space Agency, Noordwijk, Netherlands
011-31-71-565-6799
markus.bauer at esa.int 

2015-189