Is Comet Ison Kaput?

A blast of particles from the sun called a coronal mass ejection, or CME, is seen at the right of this image taken on Nov. 22 by the STEREO-A spacecraft. (The sun is not actually visible.) Comet Ison is at the extreme left of the image. A smaller comet, Encke, is also visible, as is Mercury and the Earth. It is not known for sure whether this CME actually hit Ison. But the image does provide a sense of the increasingly violent environment the comet is encountering as it comes ever closer to the sun. (Source: Karl Battams/NRL/NASA-CIOC) I've been closely following NASA's status reports about Comet Ison, which is three days out from its expected closest approach to the sun. And the latest report raises the possibility that the answer to the question posed in the headline is, well, "maybe." Karl Battams, an astrophysicist and computational scientist based at the Naval Research Laboratory in Washington DC, has been posting regular updates on NASA's Comet Ison Observing Campaign website. He has operated the NASA-funded Sungrazing Comets Project since 2003. Here's a snippet from his latest post:

We are seeing reports online that molecular emission from the comet has fallen dramatically, meanwhile dust production seems to be enormous. What this could indicate is that the nucleus has completely disrupted, releasing an enormous volume of dust while significantly reducing emission rates. Fragmentation or disruption of the nucleus has always been the highest risk factor for this comet so if this has indeed happened then while unfortunate, it would not be a surprise. However, these reports are new, and while they are undoubtedly valid, we do still need to keep observing the comet to be sure what is happening.

Here is one of the online reports he refers to, from a public Yahoo mailing list about comets:

Michal Drahus Message 1 of 17 , Today at 3:32 AM Hi All, Comet ISON has been closely monitored at the IRAM millimeter telescope in Spain by Israel Hermelo (IRAM Granada) and myself (Caltech/NRAO) for the last 6 days. We observe consistent, rapid fading of the molecular emission lines between Nov. 21 and Nov. 25 by at least a factor of 20 (likely more). This may indicate that the nucleus is now at best marginally active or that... it no longer exists. Regards, Michal

Comet Ison has been visible to NASA's STEREO-A spacecraft. And last Friday, it captured the image at the top of this post showing the result of a massive explosion on the sun called a coronal mass ejection. Look to the right of the image and you'll see it. The area of disruption that looks a bit like some sort of explosion is actually billions of tons of solar particles streaming outward toward Comet Ison and the smaller Comet Encke.

Did this CME hit Ison, and if so what impact did it have? Here's what Karl Battams had to say about it in a blog post yesterday:

The CME can be seen coming towards the comets but then... argh! We had a data gap! (Put the tin foil down! Data gaps happen all the time, and they're temporary.) We pick up the sequence a few hours after the CME has passed but there doesn't appear to be any major interaction happening so I suspect they didn't get hit, or if they did then it wasn't a direct blow. Both of these comets are directly in the line of fire for CMEs, though, so hopefully we do get a big one in the next couple of days.

So let's be clear: I didn't use the image at the top of the post to suggest that the CME has spelled doom for Comet Ison. But it does show what the comet must contend with as it nears the sun — an increasingly violent environment that could well have already spelled doom. We'll know soon enough.

In the meantime, Battams urges us to keep all of this in the right scientific perspective:

Remember: Comet ISON is a dynamically new sungrazing comet, fresh in from the Oort Cloud, and the last time we saw an object like this was never! Furthermore, a sungrazing comet just three days from perihelion has never been studied in this kind of detail - we're breaking new ground here! When we factor in your standard "comets are unpredictable" disclaimer, what we have is a huge recipe for the unknown.