From: LARRY KLAES (ljk4_at_msn.com)
Date: Tue Oct 09 2007 - 10:26:29 PDT
>From: "AAS Press Officer Dr. Steve Maran" <Steve.Maran_at_aas.org>
>To: "AAS Press Officer Dr. Steve Maran" <steve.maran_at_aas.org>
>Subject: SwRI: Pluto Probe Finds "Dramatic Changes" in Jupiter's Moon Io
>Date: Tue, 9 Oct 2007 11:13:43 -0400
>
THE FOLLOWING RELEASE WAS RECEIVED FROM THE SOUTHWEST RESEARCH INSTITUTE, IN
SAN ANTONIO, TEXAS, AND IS FORWARDED FOR YOUR INFORMATION. (FORWARDING DOES
NOT IMPLY ENDORSEMENT BY THE AMERICAN ASTRONOMICAL SOCIETY.) Steve Maran,
American Astronomical Society steve.maran_at_aas.org 1-202-328-2010 x116
Contact:
Rob Leibold
1-210-522-2258 rleibold_at_swri.org
New Horizons’ Alice UV spectrograph observes Io’s atmosphere change in
response to eclipse events
SAN ANTONIO -- Oct. 9, 2007 -- Dramatic changes in the atmospheric density
of Jupiter’s moon Io and its interaction with Jupiter’s magnetosphere
during solar eclipse were observed through Io’s aurora on four occasions
this past spring as the New Horizons spacecraft rounded Jupiter for a
gravity assist on its way to Pluto.
Scientists using New Horizons’ Southwest Research Institute
(SwRI)-developed Alice ultraviolet spectrograph, which is designed to image
ultraviolet emissions, noted auroral brightness and morphology variations as
the spacecraft entered and then exited the eclipse zone revealing changes in
the relative contribution of sublimation and volcanic sources to the
atmosphere. The findings were supported by concurrent Hubble Space Telescope
ultraviolet imaging and will be published in the Oct. 12 issue of Science.
FUV (far-ultraviolet) aurora morphology also reveals the plumes effect on
Io’s electrodynamic interaction with Jupiter’s magnetosphere.
Comparisons to simulations of Io’s aurora indicate that volcanoes supply 1
percent to 3 percent of Io’s dayside atmosphere.
Aurora observations, particularly while Io is in solar eclipse by Jupiter,
can provide information on both Io’s atmosphere and its interaction with
Jupiter, the paper states.
An aurora is a luminous phenomenon in the upper atmosphere of a planet
caused by the emission of light from atoms excited by electrons accelerated
along magnetic field lines. Most planetary aurorae occur in the polar
regions, but Io’s aurora is brightest near its equator as well as in
volcanic plumes distributed across the satellite.
“Io is volcanically active, and that volcanism ultimately is the source
material for Io’s sulfur-dioxide atmosphere, but the relative
contributions of volcanic plumes and sublimation of frosts deposited near
the plumes have remained a question for almost 30 years,” said Dr. Kurt
Retherford, a senior research scientist in the Space Science and Engineering
Division at the Institute.
The interaction between Io’s atmosphere and the Io plasma torus produces
displays of auroral emissions on Io, supplies plasma to Jupiter’s
magnetosphere and physically links Io to Jupiter, according to the paper.
“When Io goes into solar eclipse, and during the night, its surface
temperature drops significantly, causing diminished sublimation of surface
material into the atmosphere. The atmosphere at that point collapses down so
that all that is left supplying the atmosphere are the volcanoes,”
Retherford said.
A dramatic difference between Io’s dayside and nightside atmospheric
density best explains the aurorae observations, he added.
Alice provides spectral images in the extreme- and far-ultraviolet (EUV and
FUV) passbands. S. Alan Stern, NASA’s associate administrator for the
Science Mission Directorate and former executive director of the Space
Science and Engineering Division at SwRI, is the principal investigator of
New Horizons, Alice and Ralph, a visible and infrared camera onboard the
spacecraft. Prof. Joachim Saur at the University of Cologne, Germany,
conducted the simulations.
New Horizons is the first mission in NASA’s New Frontiers program. The
Johns Hopkins University Applied Physics Laboratory manages the mission and
operates the spacecraft for the NASA Science Mission Directorate. SwRI leads
the SWAP instrument and hosts the Tombaugh Science Operations Center.
The paper is titled, “Io’s Atmospheric Response to Eclipse: UV Aurorae
Observations,” by K.D. Retherford, J.R. Spencer, S.A. Stern, J. Saur, D.F.
Strobel, A.J. Steffl, G.R. Gladstone, H.A. Weaver, A.F. Cheng, J.Wm. Parker,
D.C. Slater, M.H. Versteeg, M.W. Davis, F. Bagenal, H.B. Throop, R.M.C.
Lopes, D.C. Reuter, A. Lunsford, S.J. Conard, L.A. Young and J.M. Moore.
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