Tuesday, August 30, 2011

Is NASA spacecraft observatory STEREO Behind HI-1 camera watching comet Elenin fade?

Over the last week or so the astronomical community has been abuzz about comet Elenin and its apparent fading as imaged from earth. Currently best observed from the Southern hemisphere, a small number of Australian observers have reported a diffusion and decrease in brightness of the inner coma. This is a sign that comet Elenin is running low on the volatiles necessary to keep it actively visible and may consequently completely lose its coma and tail. 

Meanwhile, NASA spacecraft STEREO B has been watching nonstop from the 14th to the 26th and seems to confirm this fading. I say seems, because, comet Elenin is heading away from the spacecraft very rapidly by the 24th as it heads for perihelion in just under two weeks from now. Comet Elenin appears to the HI-1 camera to be slowing down by the 24th when in fact it is speeding up. This is due to comet Elenin moving more directly away in close to a straight line and consequently this could be resulting in it becoming more and more faded in brightness. It appears brightest as it shows up in the normal field of view of the STEREO B HI-1 camera because of its range and also because of its coming out of conjunction with the sun, which causes it to light up a little more due to forward scattering. As of the 19th when a coronal mass ejection hit comet Elenin, which can be seen as a slight tail forming and then violently being ripped off and twirled about, there was a dramatic decrease in brightness and the central condensation that would normally be considered the inner coma became an elongated diffused blur as seen from earth based observers. The STEREO B HI-1 camera however is showing no decrease whatsoever in the days following the 19th, but does show a decrease by the 24th. The question is, is this due to the thermal imaging attribute of the HI-1 camera or is there something else happening? And the slight fading seen through the 24th to the 26th, can this be attributed to the rapidly increasing range or is this the actual fading that is being observed from earth? We will learn the answers in just a week or so from the time of this writing!