Spitzer Space Telescope Observations of the Nucleus and Trail of Comet 103P/Hartley 2

Details Spitzer Space Telescope Observations of the Nucleus and Trail of Comet 103P/Hartley 2 Spitzer Space Telescope Observations of the Nucleus and Trail of Comet 103P/Hartley 2

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.2008f&link_type=abstract

American Astronomical Society, DPS meeting #41, #20.08

Astronomy and Astrophysics

Astronomy

Scientific paper

We have used the 22-micron peakup array on the Spitzer Space Telescope's InfraRed Spectrograph (IRS) to image thermal emission from the nucleus and trail of comet 103P/Hartley 2, the target of NASA's Deep Impact eXtended Investigation (DIXI). The comet was observed for 2.7 hours on UT 2008 August 12 and 13, when it was 5.5 AU from the Sun. The comet was faint and showed a point source plus extended emission in a trail directed along the comet's anti-velocity vector. The trail is likely composed of mm-sized grains emitted at the last perihelion passage, and has an optical depth of about 2 × 10-9. We infer from this that the main dust hazard to DIXI during its flyby in 2010 will not be the grains in the trail but rather near-nuclear dust in the coma. After modeling out the trail emission, we find that the comet's point-source by itself has a flux density of 0.10±0.02 mJy, which we interpret as thermal emission from the nucleus. Modeling of this flux, using a beaming parameter of 0.95±0.20, yields an effective radius of 0.57±0.08 km. The nucleus is about one-fifth as wide (and so roughly 100 times less massive) as that of Deep Impact's first target, comet 9P/Tempel 1. Given 103P's perihelion water production rate, its radius suggests that approximately 100% of the surface would be actively emitting volatile material then. This is about 13 times the active fraction of 9P. Since the magnitude of 103P's non-gravitational orbital parameters is similar to that of the much-larger 9P, we conclude that 103P must have a much more isotropic pattern of time-averaged outgassing from its surface. From ground-based visible-wavelength imaging, we estimate the nucleus's geometric albedo to be 0.03±0.01. Support for this work was provided by NASA through an award issued by JPL/Caltech.

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