CO-2 as the driving force of comet Hartley 2's activity-An experimental study

摘要

In our experimental study we observed massive ice grain ejection driven by CO-2,during several temperature ranges when the ice is warmed up. A'Hearn et al.,2011. Science 332,1396-1400 and Meech et al.,2011. The Astrophysical Journal Letters 734,L1 among others,found that CO-2 is the major driving force of the activity of Comet 103P/Hartley 2. In our experimental studies we found that CO-2 is trapped in low temperature "cometary" amorphous water ice 3-4 orders of magnitude more efficiently than gases such as CO,CH-4 and Ar. Thus,the ice grains which agglomerated to form the nuclei of comets where CO dominates CO-2 in the coma seem to have formed in regions highly depleted in CO-2. In the experiments we observed ice grains ranging from submicron to hundreds of microns,accompanied by jets of CO-2. The experimentally observed cm size fragments,which were formed by cracking the overlying ice layer,could also be ejected under the cometary microgravity. These size ranges were also observed on Comet 103P/ Hartley 2. The smooth terrain observed on Hartley 2's "waist" is similar to the smooth terrain observed on comet Temple 1 and could have been formed by settling of ice grains ejected nearby,as observed in our experiments.