__________________________________________________________________________ T H E O L E R O E M E R M E S S E N G E R _______________________________________________ JJJJ C G JJJJJJ I E JJJJ __________________________________________________________________________ Newsletter of the International Jupiter Watch Satellite Discipline E-mail issue 2 January 6, 1992 Editor: Discipline Leader: John Spencer Jay Goguen Lowell Observatory Jet Propulsion Lab, M.S. 183-501 1400 W. Mars Hill Rd. 4800 Oak Grove Dr. Flagstaff, AZ 86001 Pasadena, CA 91109 Voice: (602) 774-3358 Voice: (818) 354-8748 Fax: (602) 774-6296 Fax: (818) 354-0966 Internet: spencer@lowell.edu Internet: jdg@scn2.jpl.nasa.gov __________________________________________________________________________ EDITORIAL COMMENTS This second issue of the new Ole Roemer Messenger contains information distributed by e-mail since the first hardcopy issue was sent out, for the benefit of hardcopy "subscribers". Please send me comments and contributions for future issues! ________________________________________________________________________ GOODIES AVAILABLE BY ANONYMOUS FTP Miscellaneous files related to the satellite discipline are now available by anonymous ftp over the Internet, from "lowell.edu" or "192.103.11.2", in subdirectory pub/ijw. Back copies of the messenger are avaiable as ASCII files with names like "roemer1.doc". A global Voyager image mosaic of Io, prepared by Alfred McEwen, is also available in compressed FITS format at a variety of resolutions. The file CONTENTS.DOC in the subdirectory gives details. ________________________________________________________________________ GALILEO SATELLITE TOUR CHOSEN The Galileo project has chosen the sequence of Jupiter orbits and Galilean satellite encounters that will follow Jupiter Orbit Insertion. The "tour", called 92-14A, will be implemented whether or not the high-gain antenna eventually opens. The highlights of the tour are as follows: Min. distance Distance from satellite, from Date (km) Jupiter (Rj) Event -------------------------------------------------------------------- 1995/12/07 ?? Close Europa untargeted flyby 1995/12/07 1000 Io targeted flyby 1995/12/07 4.1 Jupiter orbit insertion burn 1996/03/12 277.5 Apojove, perijove raise burn 1996/07/04 500 Ganymede targeted flyby 1996/07/05 10.9 Perijove 1 1996/07/05 186000 Europa "untargeted" flyby 1996/08/06 118.7 Apojove 1996/09/06 200 Ganymede targeted flyby 1996/09/07 10.6 Perijove 2 1996/10/07 113.0 Apojove 1996/11/04 1232 Callisto targeted flyby 1996/11/06 9.2 Perijove 3 1996/11/06 65475 Europa untargeted flyby 1996/11/27 89.1 Apojove 1996/12/19 9.2 Perijove 4 1996/12/19 633 Europa targeted flyby 1997/01/04 72.1 Apojove 1997/01/20 9.1 Perijove 5 1997/01/20 25187 Europa untargeted flyby 1997/02/04 72.0 Apojove 1997/02/20 635 Europa targeted flyby 1997/02/20 9.1 Perijove 6 1997/03/14 89.2 Apojove 1997/04/04 24988 Europa untargeted flyby 1997/04/04 9.1 Perijove 7 1997/04/05 2740 Ganymede targeted flyby 1997/04/21 75.9 Apojove 1997/05/06 35205 Callisto untargeted flyby 1997/05/07 1602 Ganymede targeted flyby 1997/05/08 9.3 Perijove 8 1997/06/02 100.2 Apojove 1997/06/25 414 Callisto targeted flyby 1997/06/26 76976 Ganymede untargeted flyby 1997/06/27 10.8 Perijove 9 1997/08/08 143.0 Apojove 1997/09/17 522 Callisto targeted flyby 1997/09/18 9.2 Perijove 10 1997/10/13 98.8 Apojove 1997/11/06 1000 Europa targeted flyby 1997/11/07 9.1 Perijove 11 For comparison, Voyager closest approaches to the satellites were: Io, 20,000 km; Europa, 206,000 km; Ganymede, 62,000 km; and Callisto, 126,000 km. There will be other useful approaches to the satellites at ranges greater than 100,000 km, but these aren't considered "official" flybys. In particular, Io encounters at minimum distances between 600,000 km and 200,000 km should occur on most orbits, giving from 430 to 1400 imaging pixels, or 13 to 37 NIMSels, or 3 to 7 radiometer apertures, across Io's diameter. There are possibilities for distant occultations of the spacecraft by Io on orbits 6, 9, and 10, at a minimum distance of 3 million km. None of these are definite yet, but some will probably be done. Development of detailed sequences of observations won't start until Spring 1993, when there will be a better idea of whether the High Gain Antenna will be available. The best hope for opening the antenna is right now, when the motors are being "pulsed" to drive the antenna open while the support structure is at its warmest and most extended. So far the "pulsing" has been unsuccessful, but they will keep trying! ________________________________________________________________________ DISCOVERY MISSIONS A workshop on low-cost "Discovery" missions was held at San Juan Capistrano on Nov. 16-20, 1992. Seventy-three mission proposals were presented and reviewed, of which these four concerned the Jupiter system or Jovian planets in general: ---------------------------------------------------------------- Mission Name P. I. ---------------------------------------------------------------- Jupiter Polar Orbiter Glen Orton Earth Orbital UV Jovian Observer Paul Feldman Radio Science and Astronomy Mission (RSAM) Len Tyler Giant Outer Planet Orbiters Io Mapper William D. Smythe ---------------------------------------------------------------- IO MAPPER The Io Mapper is the only Discovery proposal directly relevant to this discipline, and is described in more detail below: The Io Mapper mission would use a derivative of the Pluto microspacecraft, consisting mostly of an RTG and a high-gain antenna, the so-called "nuclear powered wok". For Io a retropropulsion module would be added for achieving Jupiter orbit, and a single scientific instrument would be carried, a "Visible and Infrared Camera" (VIC). Total dry weight would be only 244 pounds. The camera would have a 256 x 256 InSb array sensitive from 0.4 to 5.2 microns, with 32 filters and a pixel size of 4 microradians (compared to 10 microradians for the Galileo camera and 500 microradians for the Galileo NIMS). VIC also includes an 8 - 40 micron radiometer with 300 microradian pixels (compared to 2500 microradians for the Galileo radiometer). The orbit would be similar to Galileo's, with a single close Io flyby (allowing imaging at 2 meters px-1) at orbit insertion and then a "perijove raise" maneouver into a 50-day orbit with a 9 Rj perijove to reduce the radiation dose. From perijove Io can be imaged at 1 km resolution in the visible and (because of diffraction) 4 km resolution at 5 microns (compared to 125 km at 5 microns for Galileo NIMS). Volcanic thermal emission, plumes, and surface composition and albedo changes can thus be studied in much greater detail than Galileo over the 1 year orbital lifetime of the mission, and with better time coverage because Io is the main focus of the mission. The mission was classified as "high risk" by the Discovery review panel, mostly because it requires RTGs and radiation hardening and the Pluto spacecraft does not yet exist, and science return was classed as "medium" because it provided "only an incremental advance over the goals of Galileo". It is therefore unlikely to receive NASA study money in preparation for the Announcement of Opportunity that will come out in a couple of years, but JPL funding is possible to continue development of the concept in preparation for the AO. We think that Galileo's lack of focus on Io, and the greatly improved spatial resolution of the Io Mapper compared to Galileo, especially in the IR, would provide much more than an "incremental" increase in our knowledge of Io. This is even more true if the Galileo high-gain antenna fails to open and Io monitoring from Galileo is thus restricted further. There is also the possibility of using solar panels rather than RTGs and thus reducing mission risk. So we continue to be enthusiastic about this mission concept. For more information, contact Bill Smythe (issac::wsmythe, issac.jpl.nasa.gov) or Rosaly Lopes-Gautier (issac::rlopes), both at JPL, M.S. 183-601. ________________________________________________________________________ GALILEAN SATELLITE EPHEMERIS I talked to Jay Lieske at JPL recently about the problems with the existing ephemerides for the Galilean satellites. As noted in the last Messenger, infrared photometry of the occultations of Io by Europa in 1991 suggested errors of up to several hundred km in the relative positions of Io and Europa compared to ephemeris predictions, making it difficult to determine hot spot locations from occultation timings. Jay Lieske noted that very similar problems were seen in the numerous visible-wavelength photometric observations of the 1991 mutual events. The problem seems to be an unexpectedly rapid divergence of the satellite positions from predictions based on earlier series of mutual events. The ephemeris will eventually be updated to include the 1991 observations and will then provide accurate positions for the satellites during the 1991 mutual events, but this will take a year or two. ________________________________________________________________________ UPCOMING OBSERVING PLANS Due to the remodelling of the IRTF this fall, Spencer and Clark's November and December Io runs were cancelled. Plans for the winter and spring include: Who: D. Blaney, Lynch, Russell, Hackwell, M. Hanner What: Infrared Spectroscopy of Io (2-5; 8-13 microns) using the BASS Spectrograph. Why: Determine the infrared flux at all wavelengths to model thermal sources of Io; look for silicate emission features from volcanic areas; and look for variations in SO2 frost abundance correlated with thermal emission. Where: IRTF, Mauna Kea When (UT): 1993/02/07-09 Who: J. Spencer and B. Clark What: Jupiter eclipse and occultation imaging of Io, 1.6 - 4.8 microns. Why: Continued monitoring of locations, temperatures, and areas of multiple hotspots on the Jupiter-facing hemisphere. Where: IRTF, Mauna Kea When (UT): 1993/01/10; 1993/01/12; 1993/01/19; 1993/02/02; 1993/02/11; 1993/05/02; 1993/05/09; 1993/05/11. Who: J. Spencer What: Jupiter eclipse and occultation (?) imaging of Io, 1.6 - 2.2 microns. Why: Measure high-temperature disk-integrated volcanic flux, attempt 2.3 micron occultation to get disk resolution. Where: 72" Perkins Reflector, Lowell Observatory When (UT): 1993/02/27; 1993/03/01; 1993/03/08. Who: J. Spencer and W. Calvin What: 0.32 - 0.8 micron CCD spectroscopy of Io and Callisto Why: Obtain improved UV and visible spectra Where: 72" Perkins Reflector, Lowell Observatory When (UT): 1993/03/19-21. Who: J. Goguen, D. Matson, G. Veeder, D. Blaney, T. Johnson What: 5 - 20 micron lightcurve photometry and 5 micron imaging of Io Why: Monitoring of Io hot spot activity at all longitudes; heat flow. Where: IRTF, Mauna Kea When (UT): 1993/03/25-29. Who: M. McGrath, P. Sartoretti, F. Paresce, J. Clarke, J. Spencer, A. McEwen What: 2300 - 4000 A imaging of Io at several longitudes Why: Map surface and atmospheric SO2 distribution, look for surface changes since Voyager. Where: Hubble Space Telescope When: Summer 1993? Who: J. Clarke et al. What: Far-UV spectra of Io passing into eclipse Why: Observe effect of loss of sunlight on OI and SI airglow. Where: Hubble Space Telescope When: Feb-March 1993 Who: J. Clarke et al. What: 1600-3200 A spectra of Io leaving eclipse Why: Observe effect of returning sunlight on airglow and SO2 frost Where: Hubble Space Telescope When: Early summer 1993 John Clarke provides more detail on his HST observations: ...our group is planning HST spectra of Io in two sets of observations which may have some relevance to the surface in terms of SO2 frost. Over Feb.-March 1993 we hope to schedule two series of far-UV spectra of Io passing into eclipse, which will be mainly an atmospheric observation (i.e. OI 1304 and SI 1900 airglow to determine the time scale for decrease when Io passes into shadow). Early next summer we hope to schedule two sets of spectra over 1600-2300 A and over 2300-3200 A of Io leaving eclipse, which are to study the spectrum of Io after 1 1/2 hours in shadow. Ceertainly at the longer wavelengths, we are seeing the surface and SO2 frost. ________________________________________________________________________ PUBLICATIONS IN THE PIPELINE Paresce, F., P. Sartoretti, and the HST FOC instrument team, "Near Ultraviolet Imaging of Jupiter's Satellite Io with the Hubble Space Telescope", Astronomy and Astrophysics 262, 617-620. Spencer, J., R. Howell, B. Clark, D. Classen, and D. O'Connor, "Volcanic Activity on Io at the Time of the Ulysses Encounter", Science 257, 1507-1510. "Europa, Ganymede, And Callisto: New Radar Results From Arecibo And Goldstone" S. J. Ostro (300-233, Jet Propulsion Laboratory, Pasadena, CA 91109), D. B. Campbell, R. A. Simpson, R. S. Hudson, J. F. Chandler, K. D. Rosema, I. I. Shapiro, E. M. Standish, R. Winkler, D. K. Yeomans, R. Velez, R. M. Goldstein. JGR Planets 97, 18227. "Photometric Models for Galilean Satellite Astrometry" T. Mallama, Hughes STX Corp. Submitted to JGR Planets Annapolis Conference Special Issue. Abstract: Models for Io, Europa, Ganymede, and Callisto have been used to determine the distribution of brightness on their surfaces. The results indicate that the distance between a satellite's photocenter and its center-of-figure can be over 200 km. Astrometry of the satellites can achieve much greater precision than this, so a correction for the photocentric offset should be included. The ephemerides derived from astrometry are essential for interpreting observations of variable phenomena on Io, and for spacecraft navigation. This paper presents tables of photocentric offsets for the Galilean satellites as a function of orbital and solar phase angles _________________________________________________________________________ UPCOMING MEETINGS SODIUM ATMOSPHERES WORKSHOP San Juan Capistrano Institute, San Juan Capistrano, CA, 2-4 February 1993. Contact Doug Nash. IO CONFERENCE The Io conference organised by Doug Nash, to be held at the San Juan Capistrano Research Institute, now has firm dates, as follows: Indication of interest form due: Feb. 15, 1993 Abstract Deadline: May 3, 1993 Conference: Tuesday June 22 - Friday June 25 1993 The first mailing will be issued very shortly. _________________________________________________________________________