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(meteorobs) Fwd: Tool For First Comet Orbiter Will Examine Escaping Gases




------- Forwarded Message

From: Ron Baalke <baalke@zagami.jpl.nasadot gov>
Subject: Tool For First Comet Orbiter Will Examine Escaping Gases
To: astro-l@uwwvax.uwwdot edu (Astronomy List)
Date: Mon, 19 Nov 2001 17:00:18 -0800 (PST)


MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasadot gov

Contact: Martha J. Heil  (818) 354-0850

FOR IMMEDIATE RELEASE                     November 19, 2001

TOOL FOR FIRST COMET ORBITER WILL EXAMINE ESCAPING GASES

     A lightweight NASA instrument from California has arrived 
in the Netherlands, one step closer in its journey to examine 
how gases escape from the nucleus of a comet.

     The Microwave Instrument for the Rosetta Orbiter is one 
of 17 instruments that will fly aboard the European Space 
Agency's major mission to a comet. Rosetta will be the first 
spacecraft to orbit a comet, and the microwave instrument will 
be the first of its type to be sent to any solar system object 
other than Earth.

     "We'll look at the abundance of the gases, their 
temperatures, the speed at which they're coming off, and the 
temperature of the comet's nucleus," said Dr. Margaret 
Frerking, the microwave instrument's project manager at NASA's 
Jet Propulsion Laboratory, Pasadena, Calif.

     The JPL-built device was incorporated into the main 
spacecraft structure in Alenia, Italy, and arrived in 
Noordwjik, Netherlands, to begin a series of tests by the 
European Space Agency. The next step in its journey is its 
path to Kourou, French Guinea, for its January 2003 launch 
into space. Rosetta will swing near Earth and two large 
asteroids before reaching its chosen dance partner, Comet 
Wirtanen, on Nov. 28, 2011. At that point in Wirtanen's 5.5-
year orbit, the comet will be at about as far from the Sun as 
Jupiter and five times as far from the Sun as Earth.

     Rosetta will drop a lander onto Wirtanen's nucleus, and 
the orbiter will circle the comet at distances as close as 2 
kilometers (1.2 miles). 

     From the orbiter, the microwave instrument will monitor 
how the release of vapors from the comet's icy nucleus changes 
as Wirtanen moves closer to the Sun. Gases and dust escaping 
from the surface of a comet form a cloud-like "coma" around 
the nucleus and a tail pointed away from the Sun.
 
     "The spacecraft will remain in orbit around Wirtanen for 
20 months as the comet moves in from Jupiter's distance from 
the Sun to about Earth's distance," said JPL's Dr. Samuel 
Gulkis, principal investigator for the instrument. "During 
that time, the nucleus will warm significantly, and we'll be 
able to watch the whole process as the comet evolves from an 
inactive iceball to having a fully developed coma."

     The instruments onboard the orbiter will include a camera 
to study surface details, a microscope to analyze dust grains 
coming off the nucleus, spectrometers to examine surface and 
coma materials in various wavelengths, and an experiment to 
probe the comet's interior with radio waves.

     The microwave instrument is a very high frequency radio 
spectrometer, weighing about 20 kilograms (44 pounds). It is 
designed for studying water, carbon dioxide, ammonia and 
methanol gases, four of the most abundant gases from comets. 
The device is sensitive to slight differences in emission 
wavelengths from those gases, allowing it to measure the 
quantities coming off the nucleus, along with their 
temperatures and speeds.

     "We want to get a good estimate of the amount of mass 
being lost by the comet so we can play that backward to get at 
what the comet was like shortly after it was formed," Gulkis 
said. That will help pin down ideas about how comets and 
planets were produced during the infancy of our solar system.

     The microwave instrument will also be able to measure 
both the surface temperature of the nucleus and the 
temperature just below the surface. "That temperature 
difference will tell us about the insulating properties of the 
surface and help us understand the thermal physics of what's 
going on inside the nucleus," Gulkis said. 

     As Rosetta passes the stony asteroid Otawara and the 
carbon-rich asteroid Siwa on its roundabout route to Wirtanen, 
the microwave instrument will examine thermal properties of 
those minor planets' surfaces and check whether they have any 
permafrost layer leaking small quantities of water vapor into 
space.

     Online information is available about Rosetta at 
http://sci.esa.int/rosetta and about the microwave instrument 
at http://mirowww.jpl.nasadot gov . JPL, a division of the 
California Institute of Technology in Pasadena, manages the 
instrument for NASA's Office of Space Science, Washington, 
D.C.

               # # # # #

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