Activity of Comets at Large Heliocentric Distances Pre-Perihelion

Details Activity of Comets at Large Heliocentric Distances Pre-Perihelion Activity of Comets at Large Heliocentric Distances Pre-Perihelion

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.0202m&link_type=abstract

American Astronomical Society, DPS meeting #40, #2.02; Bulletin of the American Astronomical Society, Vol. 40, p.387

Biology

Scientific paper

We present observational data for five long-period and dynamically new comets (C/1999 J2 (Skiff), C/2003 A2 (Gleason), C/2001 G1 (LONEOS),C/2003 O1 (LINEAR) and C/2001 Q1 (Neat) observed at heliocentric distances between 5.8 to 14.0 AU). All of the comets exhibited activity beyond the distance at which water ice sublimation can be significant on the inbound portions of their orbits. In particular, the dynamically new comet C/2003 A2 was observed active at 11.5 AU, pre-perihelion. 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 (T 135K). We propose that annealing of amorphous water ice is the driver of activity in comets as they first enter the inner Solar System. Experimental data show that large grains can be ejected at low velocity during annealing and that the rate of brightening of the comet should decrease as the heliocentric distance decreases. 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. This material is based upon work supported by the National Aeronautics and Space Administration through the NASA Astrobiology Institute under Cooperative Agreement No. NNA04CC08A issued through the Office of Space Science, by NASA Grant No. NNX07A044G.

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