ISON Image of the Week

Three Eyes on ISON  (Dec 02, 2013)

It may be (almost) gone but comet ISON leaves a legacy of unprecedented data from numerous locations within the solar system! [Image credit: ESA, NASA, Annotations by Karl Battams]
By now, we suspect that most people realize the sad fate of comet C/2012 S1 (ISON). For months it had taunted us with alternating flare-ups and periods of inactivity, before putting on a dazzling show through November resulting in some stunning ground-based observations of the comet. In the days and hours prior to its close brush with the Sun, ISON continued this dynamic and unpredictable behavior, giving us a little scare on the way to a peak brightness of approximately magnitude -3 around 12-hours before perihelion, and raising hopes for a worldwide public.

But then things kind of went downhill for ISON. Its brightness rapidly fell off over the next few hours, leading many comet experts to feel that this marked the point at which the comet's nucleus finally succumbed to the intense bombardment of solar radiation and brutal stretching and shearing forces exerted by the Sun's immense gravitational pull. Compounding the problem, we also believe this turning point occurred around the time that the comet's nucleus surface temperature would have reached the point that all material - not just ices - would begin to vaporize.

We feared the worst as ISON plunged through the solar corona, and while our hopes were briefly raised when something emerged from behind the solid LASCO C2 occulting disk, it soon became apparent that ISON was no longer a healthy comet. Within a day or so following perihelion, our last last remaining hope began to fade as quickly as the comet itself, and by November 30, 2013, a ghostly cloud was all that appeared to remain of comet ISON.

While it is conceivable that small chunks of ISON's nucleus still exist, that possibility looks increasingly unlikely and it is with more than a little sadness that we have to declare the comet lost.

But rather than mourn what we have lost, we should perhaps rejoice in what we have gained: namely, what is arguably the largest and broadest cometary data set in history compiled by more ground and space-based telescopes than ever before. In this weekly feature, it is the latter we highlight as the solar spacecraft fleet took center stage during ISON's solar plunge. The above montage shows a post-perihelion view of comet ISON taken by three different spacecraft at roughly the same moment in time, all viewing from very different locations in the solar system.

There is no question that this set of images is truly unprecedented, giving us near simultaneous views from three perspectives of comet ISON. Such images are going to be invaluable in helping us piece together the 3D structure of ISON's dust trails, and build up the picture of when the nucleus fell apart and the distribution of the sizes of the resulting material, for example.

There's much more science than this in here, and those results will come out in good time. But the point we want to convey here is that even though ISON may be gone, what it has left us is a legacy in the form of a massive data set that will teach us a tremendous amount about comets, their composition, and the processes that they undergo. One of the fundamental questions we have about comets is "how are they constructed?", and sometimes the best way to find out how something is put together is to pull it apart - and like it or not, that's exactly what the Sun did for us on November 28th, 2013.

Every week this year we will put up a new image related to Comet C/2012 S1 (ISON). If you have a cool image you'd like us to consider, please send it to, along with a description and any credits you would want applied. We'll contact you if we choose to use your image on the CIOC Website.

See our ISON Image of the Week Archives for earlier picks!