JOINT SEMINAR—the Department of Physics and Astronomy and the Centre for Planetary Science and Exploration (CPSX)
Date: Tuesday, 9th October 2012
Time: 1:30 p.m.
Location: Physics & Astronomy Room 100
Dr. Henry (Jay) Melosh
Department of Earth and Atmospheric Sciences
Purdue University
“Tiny Worlds of Ice and Grit: Results from NASA’s Most Recent Comet Missions”
ABSTRACT
NASA’s most recent successes in exploring new worlds took place on November 4, 2010 and February 14, 2011 when two spacecraft made close passes by comets Hartley 2 and Tempel 1. Although small, Hartley 2 turned out to be a feisty customer, blasting huge quantities of CO2 gas and water vapour into space, along with dust and tarlike organic material. Images from the spacecraft show an elongated nucleus about 2.0 km long, shaped like a peanut. It is divided into two major lobes separated by a smooth collar. The lobes are sources of powerful jets of gas and dust that loft chunks of material into space. Its surface is pitted, ridged and littered with blocks of ice and dust tens of metres in diameter. Tempel 1—the target of the Deep Impact collision in 2005—is much larger, seems to lack clumps of material and appears to be composed of a fine, weak powder. It nevertheless possesses a complex geologic history, with layers, crater-like depressions and what appear to be several “volcanic” flow deposits. In this presentation I will show images of these comets’ surfaces and discuss what these observations mean, so far as we currently understand them. Many of the observed phenomena, such as the jets of gas and dust, defy current understanding of how gas and dust interact in a vacuum under low gravity. The ices present in the comets are yielding important clues to conditions in the nebula from which the comets, and our own planet, originally formed.