Activity in Distant Comets - Ice Condensation Temperatures in the Early Solar System

by Karen Meech (University of Hawaii, NASA Astrobiology Institute)

Thursday 5 Nov 2009, 10:30 → 12:00 Europe/Stockholm

FA31

Long-period and dynamically new comets (those making their first passage through the inner solar system) have long been known to be active (exhibiting dust tails) in the distant solar system, beyond the distance where there is sufficient energy for water ice sublimation. This talk will present a historical overview of active comets in the context of what we are learning from space missions, laboratory ice experiments, thermal modeling and observations using large ground-based and Earth-orbital facilities. We have conducted experiments on gas-laden amorphous ice samples and show that considerable gas omission occurs when the ice is heated below the temperature of the amorphous-crystalline ice phase transition. We propose that annealing of amorphous water ice is the driver of activity in comets as they first enter the inner Solar System. These results are consistent with both historical observations of distant comet activity and with the data presented here. The ice annealing process can only release gases at temperatures above the temperature at which the amorphous ices condensed. Thus, if observations of the onset of activity in a dynamically new comet are ever made, the distance at which this occurs would be a sensitive indicator of the temperature at which the comet had formed. New surveys such as Pan STARRS, may be able to detect these comets while they are still inactive.