November 21, 2013 - Two wing-shaped features in the thin atmosphere around the head of Comet ISON were detected earlier this week by scientists from the Max Planck Institute for Solar System Research (MPS) in Germany. You can see them in the image above -- it looks almost like a cartoon angel gliding through the night sky.
The wings in the image were not immediately visible to the naked eye, however. They were revealed after the researchers eliminated the uniformly bright background of the comet's atmosphere in the image, uncovering the fainter structures that it was outshining.
The researchers did the same futzing with two images of the comet -- one taken Nov. 14 and one taken Nov. 16. While the wings were faintly detectable on Nov. 14, they dominate the Nov. 16 image, according to a news release from the institute.
Scientists at MPS suggest that the wings are a result of the comet fragmenting.
"Features like these typically occur after individual fragments break off the nucleus," Hermann Böhnhardt of the MPS said in a statement.
If a fragment did indeed break off the comet, that could also explain why it was seen to brighten suddenly, and considerably, in mid-November. Just like the nucleus of a comet, fragments also release dust and gas that can reflect the light of the sun. According to the MPS news release, the wings can occur where emissions from the comet and its fragments meet.
If this is the case, then Comet ISON has a much-reduced chance of surviving its close brush with the sun on Nov. 28.
"According to past experience, comets that have once lost a fragment tend to do this again," Böhnhardt said.
But not everyone agrees with this analysis. On NASA's Comet ISON Observing Campaign blog, Karl Battams writes that the wings look a bit too symmetrical to have been caused by nucleus fragmentation. He suggests the wings might be caused by jets in the comet's nucleus shooting dust off the comet, or that they might have been caused by a change in the solar wind.
Who is right, and will Comet ISON survive its close pass with the sun to dazzle us in early December? Only time will tell.