Comet ISON, expected to thrill, may be dying

What was once heralded as the potential “Comet of the Century” may be an equally large disappointment. Although previous reports of the comets demise may have been significantly exaggerated, new information reveals that not only is the comet underwhelming as it races towards the sun — it is also smaller than expected, and tracking in a very dangerous area for comets that wish to survive.

The comet recently passed near Mars, where NASA utilized several imaging tools to view it. It was this imaging, coupled with thousands of others which have been taken over the last several months, which revealed that Comet ISON may not be what it was initially perceived to be. The comet, which was discovered over a year ago and began brightening ahead of schedule, would have eventually reached a magnitude of -17 if it had continued to brighten at such a rate. But, over the last 4-6 months, the comets brightening has “stalled”. And this is bad, bad news for those who are hoping for a bright comet this autumn and winter.

Comet ISON as observed by the Hubble Space Telescope near Jupiter, in April of 2013.

ISON’s roots can be traced back to the Oort Cloud, a dusty mass in the far reaches of the universe. The comet was sling-shotted out of the Oort Cloud — will pass through our solar system over the next few months, and then will very likely disappear back into space never to be seen again. But the business of predicting comets brightness is a tricky one. After all, they are somewhat rare — and we are not excellent at predicting these types of arguably naturally unpredictable events.

Initial reports and imagery of the comet came with great excitement. ISON was on a path which historically featured some of the brightest comets observed. Additionally, the comet was already bright — and still brightening at a great speed. A continued brightening at the same pace observed in January and February 2013 would have led ISON to a magnitude of -15 or -17, as bright or brighter than the full moon in the night sky.

Then, the problems started. Some time during the months of January and February 2013, Comet ISON’s brightening slowed and eventually nearly stalled. The comet was expected to receive a bump as it neared the sun this summer, but that never occurred. Instead, the comet’s brightness remains nearly the same. Columbian astronomer Ignacious Ferrin believes this signals the end for Comet ISON.

Comet ISON as observed in late September 2013, just prior to its close pass to Mars. The comet was not brightening as expected.

Using secular light curves, assembled from thousands of observations, Ferrin has observed features in Comet ISON that have been observed in other disintegrating comets. “The light curve of the comet exhibited a slowdown event characterized by a constant brightness with no indication of a brightness increase tendency”, Ferrin said in a statement. In other words, ISON is heading down a path which other comets have before — and they haven’t survived. “When I saw this signature I immediately went to my database of comet light curves, and found that two comets had also presented this signature: Comet C/1996 Q1 Tabur and comet C/2002 O4 Honig; to my surprise these two comets had vanished turning off or disintegrating.”, Ferrin said.

In addition to being smaller and less bright than expected, Comet ISON is on a dangerous path. Called “Roche’s limit” the comet is expected to enter an area close to the sun where comets similar in size are nearly certain to break up. The dust production rate of ISON is also underwhelming, leading to new projections showing that ISON may never even crack naked-eye visibility this autumn.

While it is hard to say exactly what will become of Comet ISON in the next month or two, tracking projections and data present a challenge and interest for us all. And it is fair to say, with a good degree of certainty, that we will all be paying close attention to ISON over the next few months — whether it ends up lighting up the night sky or not.