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April 6, 2018 | 3:30 p.m. - 4:30 p.m.
Category: Seminar
Location: Physics #312 | Map
666 W. Hancock
Detroit, MI 48201
Cost: Free!
Audience: Academic Staff, Current Graduate Students, Current Undergraduate Students, Faculty

Title: Breaking the Ice: How Sublimative Torques Alter and Destroy Cometary Bodies

Speaker: Jordan Steckloff (Planetary Science Institute, Tucson and University of Texas at Austin)

Abstract: To quote David Levy: "comets are like cats: they have tails, and they do precisely what they want." Comets are small ice-rich solar system objects that sublimate vigorously near perihelion. These sublimating gases entrain fine dust grains as they escape, forming a gas and dust cloud that can be seen from the Earth.  Recent spacecraft missions to comets have found that that have strange bilobate shapes, undergo outbursts (rapid, unpredictable brightening events), and form long striated dust features in their tails that somehow align with the Sun rather than the nucleus. Additionally, their dynamics appear to require some mysterious mechanism for activating their sublimative activity. In this talk, I describe how all of these features are the result of ice sublimation, the process that defines these irregularly shaped bodies.

Comets are too small to retain a significant atmosphere.  Thus, the escaping, rarefied sublimating gases are asymmetrically distributed about the nucleus.  This asymmetric sublimative mass loss generates torques that change the rotation state of the nucleus.  Such rotational spin-up can induce internal stresses that fission the nucleus, forming cometary striae and preserving the strange bilobate shape of 67P/Churyumov-Gerasimenko. Additionally, the concentration of activity at the small lobe of 103P/Hartley 2 (and the activation/reactivation of comet nuclei more generally) is likely the result of avalanches triggered by such changes in the rotation state of the comet nucleus.  Such avalanches may also cause highly collimated outburst plumes, such as those observed at 67P/Churyumov-Gerasimenko, which have thus far evaded explanation.

For more information about this event, please contact Matt Barrett at +1 313 5770750 or