From: IN%"kent.tobiska@jpl.nasa.gov" "W. Kent Tobiska" 28-OCT-1998 22:07:23.77 To: IN%"David.A.Senske@jpl.nasa.gov" CC: IN%"hendrix@pisces.colorado.edu" "Amanda Hendrix", IN%"barth@pisces.colorado.edu" "Charles Barth", IN%"hord@pisces.colorado.edu" "Charlie Hord", IN%"stewart@pisces.colorado.edu" "Ian A.F. Stewart", IN%"adams@lasp.colorado.edu" "Jim Adams" Subj: UVS/EUV prime mission science highlights Return-path: Received: from eis-msg-014.jpl.nasa.gov by pisces.colorado.edu (PMDF V4.2-13 #26137) id <01J3IPUGT2IOHSJ58K@pisces.colorado.edu>; Wed, 28 Oct 1998 22:05:38 GMT Received: from [137.78.240.45] (karakh.jpl.nasa.gov [137.78.240.45]) by eis-msg-014.jpl.nasa.gov (8.8.5/8.8.5) with ESMTP id OAA01498; Wed, 28 Oct 1998 14:07:34 -0800 (PST) Date: Wed, 28 Oct 1998 14:10:43 -0800 From: "W. Kent Tobiska" Subject: UVS/EUV prime mission science highlights To: David.A.Senske@jpl.nasa.gov Cc: Amanda Hendrix , Charles Barth , Charlie Hord , "Ian A.F. Stewart" , Jim Adams , Joe Ajello , Karen Simmons , Kent Tobiska , Lisa Crowell , Wayne Pryor , Wendy Sweet Message-id: MIME-version: 1.0 Content-type: text/plain; charset="us-ascii" Content-transfer-encoding: 7BIT X-Sender: ktobiska@pop.jpl.nasa.gov ********************************************************************* UVS/EUV prime mission science highlights for the "Galileo Messenger." MWG: 1) Io torus: EUV measurements show that the Io Plasma Torus varies between a bright, dense, cool state and a dimmer, less dense, and warmer state. Voyager discovered the IPT in the latter state. It is likely that the denser state results from an increased rate of gain of material (sulfur and oxygen) from Io, perhaps linked to increased volcanic activity. 2) Io neutral cloud: The extended atmosphere of neutral O and S observed from SI and OI resonance lines is in agreement with HST at Io. SWG: 1) Ganymede: Characterization of tenous hydrogen atmosphere on Ganymede with a 450 K exosphere and possible source from UV photodesorption or magnetospheric ion plasma sputtering of water ice. Also, in the near-UV an ozone-like absorption feature has been detected, likely due to bombardment by charged particles on Ganymede's trailing hemisphere. The absorber appers to be destroyed by sunlight (converted into molecular oxygen) but survives in the low-sun regions of the poles and near the terminator. 2) Europa: In near-UV low-resolution observations, an "SO2-like" absorption feature becomes stronger closer to trailing hemisphere apex, where the corotating magnetospheric plasma sweeps by Europa. Higher resolution observations from the primary mission and continuing into the GEM are showing that the absorption feature is also related to certain terrain types. The absorption feature may be due to a combination of implantation/sputtering by the magnetospheric plasma and endogenic processes at the surface. 3) Io: Near-UV observations show variations in amount of SO2 frost as well coverage by and thickness of patchy SO2 gas regions. The SO2 gas varies in thickness depending on SO2 frost sublimation and volcanic plume/hotspot activity. 4) Callisto: Callisto also has a tenuous atmosphere of about three times less hydrogen as Ganymede. Ganymede's escaping hydrogen is likely due to a combination of 1) charged particles impacting the water ice surface, ejecting hydrogen atoms, and 2) ultraviolet photodesorption causing ejection of hydrogen atoms from the surface water ice. In contrast, Callisto's escaping hydrogen is likely due mostly to ultraviolet photodesorption, as there are less charged particles at Callisto's orbit to break up the water ice than at Ganymede's orbit; there is also less exposed water ice at Callisto's surface than on Ganymede's surface to serve as a source of escaping hydrogen. AWG: 1) Jupiter aurora (EUV): North and south polar observations of H2 show a wide range of altitudes for aurorae. 2) Jupiter aurora (FUV): The first detection of H2 a-b transition in astronomy is made along with the characterization of the Jovian aurora as having an important component source of secondary electrons. 3) Jupiter thermosphere: Hydrogen bulge is stable from Voyager to Galileo and newly discovered non-bulge H enhancements and depletions may be caused by coupled energetics from lower atmosphere features via gravity waves. 4) Jupiter features: (???? - Wayne - ammonia?) 5) S-L 9: UVS measured the extremely hot bolide entry phase of fragment G of Comet Shoemaker-Levy 9. A bright signal was seen at 292 nm for a 1.6 s interval, and was not seen in observations made 5.33 s earlier and later. Comparison with PPR data confirm that UVS saw the initial bolide flash, with a blackbody temperature of 8000 K and an area of about 40 square km. The subsequent cooler emissions at longer wavelengths from the expanding fireball were tracked by PPR and NIMS. ************************** W. Kent Tobiska FDC/JPL, MS 264-580 4800 Oak Grove Dr. Pasadena, CA 91109 (818) 393-7742 (phone) (818) 393-4530 (fax) kent.tobiska@jpl.nasa.gov **************************