[meteorite-list] EPOXI Mission Status - September 14, 2010

[Ron Baalke]

http://epoxi.umd.edu/1mission/status.shtml

EPOXI Mission Status
Michael A'Hearn
EPOXI Principal Investigator
September 14, 2010

We have now been observing the comet for about a week (we began
on Sunday, 5 September). After the first day it was clear that portions
of the spacecraft were getting hotter than we had predicted. The
previously agreed procedure was executed to turn off the HRI, which
generates a moderate amount of heat in the parts of the spacecraft near
the telecommunications system. As we approach the comet, the geometry
changes enough to make the instruments and the other parts of the
spacecraft fit better into the shadow behind the solar panels so things
will cool off and we can turn the HRI back on. Although we had planned
on taking HRI images during this period, we had not scheduled any
spectroscopy until the end of September and we expect to have the
instrument turned back on by then.

We have begun preliminary analyses of the images from the MRI and we can
already see variations in the brightness that appear to be correlated
with the rotational period that has been previously announced by
ground-based observers (Knight et al., IAU Circular 9163), namely 16.6
hours. At this time we only take observations every 6 hours because of
the heating of the spacecraft, so we do not yet have enough temporal
resolution to separate how much of the variation is due to the varying
cross-section of the nucleus and how much is due to activity, but it
seems clear that there is some variation in activity, possibly including
at least one short-duration outburst.

In our images, the coma is seen to extend several tens of thousands of
km (Image 1 <http://epoxi.umd.edu/3gallery/Hartley2_first_light.shtml> 
released 8 Sep; Image 2 <http://epoxi.umd.edu/3gallery/20100913_103P.shtml> 
released 14 Sept). As a point of comparison, at the time of the previously 
released image (5 Sept), the comet was 0.40 AU from the spacecraft but 
only 0.36 AU from Earth.  We will be looking for any structure in the 
images and whether that structure varies with rotation.