From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Oct 10 2007 - 13:39:05 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: Rare Look at Jupiter's Night Side
>Date: Wed, 10 Oct 2007 16:20:53 -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:
Deb Schmid
1-210-522-2254 dschmid_at_swri.org
For immediate release
San Antonio -- October 10, 2007 -- The New Horizons spacecraft, en route to
Pluto, has taken a rare look at Jupiter's night side, yielding some
surprising data about the aurora and ultraviolet light emanating from the
gas giant. Southwest Research Institute scientists, checking out the
instruments and testing mission maneuvers in a dress rehearsal for the main
event at the edge of the solar system eight years hence, collected reams of
Jovian data that have resulted in a paper outlining unexpected discoveries
about its nightglow and aurora (one of a group of papers reporting on the
New Horizons flyby of Jupiter) in the Oct. 12 issue of the journal Science.
In 1979, the Voyager spacecraft provided the first look at ultraviolet light
from the night side of Jupiter. Since then, scientists have examined
extensively the gas giant's dayside, and based on the data, developed
detailed models of the Jovian system. However, the New Horizons data that
scientists expected to see, in terms of UV light, and what they found, are
as different as night and day.
"We can't see the night side of Jupiter from Earth," said Dr. Randy
Gladstone, an Institute scientist in SwRI's Space Science and Engineering
Division and lead atmosphere scientist for the New Horizons mission. "We
only get a chance when a spacecraft goes there, and the New Horizons flyby
is one of only a handful of looks we've had of the night side of Jupiter."
Although the Voyager flyby detected marked ultraviolet night-side emissions
of the signature Lyman-alpha glow of atomic hydrogen almost 30 years ago,
data collected by the SwRI-developed Alice UV spectrograph this spring
showed almost none.
Additionally, the auroral energy deposited at night in Jupiter's upper
atmosphere has the opposite dependence with local time as occurs on the
dayside. A fortuitous observation of visible emissions associated with the
interaction between Jupiter and its satellite Io shows that they are
structured and that they extend to a surprisingly high altitude.
The substantial night-time airglow observed by Voyager in 1979 and Galileo
in1996-1997 suggested low-latitude particle precipitation, which could
contribute to the heating of Jupiter's unusually hot upper atmosphere and
account for low-latitude X-ray emissions. In contrast, the new observations
by New Horizons indicate no substantial low-latitude particle precipitation
is currently occurring, and that Jupiter's upper atmosphere must have
significantly changed between these epochs. These results are even more
puzzling, because the Voyager flybys occurred during solar maximum, while
Galileo observations and the New Horizons flyby both took place during solar
minimum.
Auroral spectroscopy from both the Hubble Space Telescope and the
Ultraviolet Imaging Spectrograph on Cassini has shown that the most
energetic of Jupiter's auroral particles are found on the dawn side of the
planet, as seen on the dayside from the vantage point of Earth. In contrast,
the Alice UV scans indicate the most energetic auroral particles on the
night side of Jupiter are located near dusk. This is unusual because, unlike
on Earth, Jupiter's auroral oval rotates with the planet, and most features
of the aurora do likewise.
"This is a surprising result. The energetic electrons responsible for these
night side emissions are probably from high latitudes connected to the dusk
flank of the magnetosphere, which is also fixed in solar local time,"
Gladstone said. "However, there are some other features of the main auroral
oval that remain fixed in local time and don't appear to rotate. The Alice
data imply that the energy of precipitating electrons is highest just after
sunset and decreases as the night goes on at Jupiter."
Observing the Io Flux Tube, a cylinder of magnetic flux formed by Jovian
magnetic field lines that transiently interact with the atmosphere of the
satellite Io, was serendipitous. New Horizon's Long Range Reconnaissance
Imager or LORRI visible camera only planned to observe the main Jovian
aurora, however, the timing was right to catch the Io Flux Tube in profile
right at the edge of Jupiter. The resulting images show that the spot of
aurora that occurs when electrons in the Io Flux Tube hit the atmosphere of
Jupiter has considerable structure and extends to more than 1,000 km above
the planet. The high altitude of the emissions may indicate that electrons
in the Io Flux Tube are less energetic on the night side than on the
dayside.
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. Southwest
Research Institute is lead investigator of the SWAP instrument, developed
the Alice instrument and hosts the Tombaugh Science Operations Center. Dr.
S. Alan Stern, of NASA Headquarters and former executive director of SwRI's
Space Science and Engineering Division, is the principal investigator of New
Horizons and Alice.
The paper, "Jupiter's Nightside Airglow and Aurora," by Gladstone, Stern,
D.C. Slater, M. Versteeg, M.W. Davis, K.D. Retherford, L.A. Young, A.J.
Steffl, H. Throop, J.W. Parker, H. A. Weaver, A.F. Cheng, G.S. Orton, J.T.
Clarke, and J.D. Nichols will be published in the Oct. 12 issue of Science.
Editors: An image to accompany this story is available at
http://www.swri.org/press/2007/nightJup.htm
SwRI is an independent, nonprofit, applied research and development
organization based in San Antonio, Texas, with more than 3,000 employees and
an annual research volume of more than $455 million. Southwest Research
Institute and SwRI are registered marks in the U.S. Patent and Trademark
Office. For more information about Southwest Research Institute, please
visit newsroom.swri.org or www.swri.org.
--------------------------------------------------------------------------
If you do not wish to receive press releases that are forwarded to the news
media by the American Astronomical Society, just reply accordingly to any
incoming press release, or write to steve.maran_at_aas.org. Requests for
referrals to experts on astronomy and space exploration should be sent to
the same address. Steve Maran, AAS Press Officer steve.maran_at_aas.org
Telephone 1-202-328-2010 X116
--- Message scanned for viruses and dangerous content by the AAS MailScanner, and is believed to be clean.
This archive was generated by hypermail 2.1.6 : Wed Oct 10 2007 - 13:44:39 PDT