From spencer@lowell.edu Sun Dec 10 19:22:40 1995
From spencer@lowell.edu Sun Dec 10 19:22:40 1995
From: spencer@lowell.edu (John R. Spencer)
Date: Sun, 10 Dec 1995 19:16:26 -0700
To: oleroemer@lowell.edu
Subject: Io and Galileo
Cc: spencer@lowell.edu
Status: RO
Content-Length: 2900
X-Lines: 56


The NASA Infrared Telescope Facility (IRTF) program of daily
observations of Io in support of the Galileo encounter ended today,
after a week of almost-daily 8.8 - 20 micron photometry of Io with the
MIRAC2 mid-IR camera, using the polypropylene sunshade over the
primary.  The solar elongation is now down to 6.5 degrees (don't try
this at home...).  We have observed Io eight times in the past week,
well scattered in longitude, though the data quality varies and is
never great at 8.8 microns, where we expect the most diagnostic
information on volcanic activity.  Our best 8.8 micron detections are
when Loki is on the disk, which may or may not be significant: we
haven't done proper photometric reductions yet.  I'm not aware of any
planned Io volcano observations after this until February, except for
the daily NSFCAM IRTF Galileo monitoring program, started this fall,
which may attempt some sunlit imaging of Io in January.

The MIRAC Io team is John Spencer and Jay Goguen, with assistance over
the past week from Glenn Orton, Padma Yanamandra-Fisher, Sarah Stewart,
Bill Hoffmann, Jim Friedson, and Bill Golisch.

The IRTF Galileo monitoring program with the NSFCAM near-IR camera will
be suspended temporarily between sometime in February and May 7th, when
it will resume taking infrared images of Jupiter and Io every
day that weather permits and NSFCAM is on the telescope for the rest of
the year.  The exception will be a break sometime in the Fall of 1996
when the IRTF will be closed for maintainence for 45 days.

GALILEO NEWS

Galileo probe data are being returned to Earth starting today:
about half the data will be returned in the next few days, the
rest will have to wait till after solar conjunction.  Glenn
Orton tells me he has had a look at some of the data but he
can't talk about it till the press conference, which will be
on Tuesday 19th December, at Ames.

Information on the re-scheduling of the Galileo G1 encounter, adapted
from a message from Terry Martin to the Galileo Atomspheric Working
Group.  The Ganymede encounter has been moved from July 4th to June
27, 1996.

  The low Io encounter (closer to Io by 112 km than planned) implies that
  it would take a lot of propellant to get us to G1 on the planned date
  (perhaps 12 kg), so the plan is to get to G1 one rev = 1 week earlier.
  Then G1-G2 cruise will be one week longer, so we get to G2 on the
  original timeline. The flyby at G1 will be about 841 km vs. 500 km
  originally.

Due to the orbital resonance, Io and Europa (but not Callisto) will be
in almost the same places on June 27th as on July 4th, so the planned
Galileo Io observations, and any Europa observations, should not
require a lot of redesign as a result of the change of date.  However,
planned observations of the Great Red Spot will now no longer occur
very close to the Ganymede encounter, which will give everyone more
time.