<p><b>THURSDAY, JANUARY 19<br>
Astronomy Colloquium, Phillips Auditorium, 60 Garden St.<br>
<br>
</b></p>
<p>4:00 pm: <a href="http://www.cfa.harvard.edu/colloquia/latest.html" target="_blank">Colloquium</a>.
"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, <a href="mailto:dgreen@cfa.harvard.edu">dgreen@cfa</a>, ext. 5-7440.) Preceded by tea at 3:30 pm. Phillips Auditorium.
</p>
<p>
<i>Abstract</i>: 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. </p>
<br clear="all"><a href="http://www.cfa.harvard.edu/cfa/calendar/latest.html">http://www.cfa.harvard.edu/cfa/calendar/latest.html</a><br>
<br>-- <br>Sarah T. Stewart-Mukhopadhyay<br>Asst. Professor of Planetary Science<br>Dept. of Earth & Planetary Sciences, Harvard University<br>Office 617.496.6462 Lab 617.496.5782 Fax 617.496.7411<br><a href="mailto:sstewart@eps.harvard.edu">
sstewart@eps.harvard.edu</a><br><a href="http://www.fas.harvard.edu/~planets/sstewart/">http://www.fas.harvard.edu/~planets/sstewart/</a><br>