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Project Progress

After the successful completion o the Deep Impact (DI) mission in 2005, an extended mission was approved, called EPOXI, which combined extrasolar planet transit observations (EPOch) and a Deep Impact Extended investigation (DIXI) to explore the nucleus of a new comet. The goal of the DIXI misison is to search for outbursts and sources, make IR spectral maps in the coma and of the surface, look at the thermal conductivity of the surface materials and correlate the surface albedo and color with topography in order to compare a new nucleus to the suite of 4 primitive small bodies that have been previously visited by in-situ spacecraft. At the time of the selection of the target, 103P/Hartley 2, the comet’s orbit had been well-observed at 4 apparitions, but the nucleus had never been detected. The Earth-based observing campaign coordinated by our team is designed to characterize the nucleus prior to encounter, specifically to get the rotation period to 20% accuracy, understand the size and albedo of the nucleus and monitor the activity pre-encounter. The challenge was that the comet is typically very active far from perihelion, producing a large coma and tail, which prevents direct observation of the nucleus. Thus nucleus observations are challenging requiring coordinating the world’s largest telescopes in combination with the Hubble Space Telescope. An observing campaign utilizing the Large Binocular telescope, The Gemini N and S telescopes, and the Hubble Space Telescope, the ESO Very Large Telesocpe, the Gran Canary Telescope and the South African Large Telescope was coordinated during March-May 2009 to secure the rotation period. The data indicate that the period is around 16.4 hours, the nucleus is relatively small, near 0.5 km, and that the nucleus may not be ellipsoidal, having a flattened shape.

The Stardust-NExT mission utilizes the Stardust spacecraft to re-visit the Deep Impact nucleus to attempt to image the crater that was not seen during the DI encounter because there was so much dust, and in addition to look at changes that occur on a comet nucleus between two successive perihelion passages. The challenge was to be able to predict the rotation period with sufficient accuracy that the final trajectory correction maneuver in Feb. 2010 would allow the spacecraft to fly past the side of the rotating nucleus that had the impact crater a year later. Not only is it known that the rotation period is changing each perilhelion passage, but that the rate of change is increasing from the outgassing torques. An intense international campaign has been planned for fall 2009, with time awarded on HST (just after the servicing mission), and telescopes in Hawaii, Arizona, Tenerife, China, Korea and India.