[Baps] Mike A'Hearn, Deep Impact Talk, Thurs Jan 19 4pm, CfA

[Sarah Stewart-Mukhopadhyay]

*THURSDAY, JANUARY 19
Astronomy Colloquium, Phillips Auditorium, 60 Garden St.

*

4:00 pm: Colloquium <http://www.cfa.harvard.edu/colloquia/latest.html>.
"Deep Impact: Excavating Comet Tempel 1," Prof. Michael A'Hearn, University
of Maryland. (Anyone wishing to meet with the speaker should contact the
host, Dr. Daniel Green, dgreen at cfa <dgreen at cfa.harvard.edu>, ext. 5-7440.)
Preceded by tea at 3:30 pm. Phillips Auditorium.

*Abstract*: On 4 July 2005, Deep Impact delivered 19 Gjoules of kinetic
energy to comet 9P/Tempel 1. On approach, we learned that outbursts by
comets are far more common than previously realized and that they can be
associated with regions on the surface. We can confidently rule out exogenic
sources for these outbursts. The geology of the surface is clearly different
from that of the few other cometary nuclei visited and very puzzling. There
are clearly distinct layers, which are likely not complete shells. Surface
photometric properties are reasonably uniform except in a few small areas.
The impact itself was oblique. Most ejecta were cold, slow-moving,
few-micron sized particles. After the first second, the ejecta include small
crystals of ordinary ice, indicating excavation without heating and thus
without chemical alteration. The ejected gases included a large amount of
CO2 and a very large amount of organics in addition to water and species yet
unidentified. The refractory to volatile ratio in the ejecta is greater than
unity but not dramatically so. The ejecta enable us to determine both the
strength of the surface layers at scales from microscopic to a few hundred
meters and the bulk density of the nucleus, which must be extremely porous.
This talk will present the current state of our rapidly evolving
understanding of comet Tempel 1.

http://www.cfa.harvard.edu/cfa/calendar/latest.html

--
Sarah T. Stewart-Mukhopadhyay
Asst. Professor of Planetary Science
Dept. of Earth & Planetary Sciences, Harvard University
Office 617.496.6462 Lab 617.496.5782 Fax 617.496.7411
sstewart at eps.harvard.edu
http://www.fas.harvard.edu/~planets/sstewart/
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