ISON Image of the Week

There's No More Ice On ISON  (Dec 16, 2013)

This image, taken on Dec 11, 2013, could have been dominated by a visually stunning Comet ISON. Sadly, instead, there is nothing to see but stars. [Image credit: Lorenzo Comolli (Italy)]
There are a couple of different ways this week's Image of the Week could have gone. In one reality, we could have been posting one of a number of truly stunning recent images of comet ISON which, having survived its passage through the Sun's million degree atmosphere, now dominates the northern hemisphere night skies!

Alas, we do not live in that reality. Instead we exist in a universe in which comet ISON was simply too small, too fragile, and too volatile to survive its close brush with the Sun. As the comet neared perihelion, it was seen to dramatically fade in the hours immediately before close approach and while a dusty something did emerge from the solar atmosphere several hours later, it was merely a ghost of its former self.

Within days, the dust cloud formerly known as Comet ISON became faint and diffuse, and hopes of a visual object in the night skies were blown away like dust in the solar wind.

We are, however, still left with the question of what remains of the enigmatic ISON? Simply dust and nothing else? Or are there perhaps a few small chunks of burned out rock, still floating along in the original orbit? One thing we do know for sure is that clearly there are no ices and volatiles that remain - and as it is the presence of those that define a comet, then there is no comet left either.
But more interesting is how we determine that there's nothing icy and volatile left, and for that we initially turn to our invaluable ground troops: amateur astronomers!

As we have stated on this website previously, professional astronomers can't just grab the nearest 20-meter telescope or commandeer Hubble at our every whim. We have to submit observing proposals to those facilities and, even when accepted, many of these facilities have strict observing restrictions when it comes to near-Sun objects. So until we can make use of the Hubble Space Telescope, for example, we are reliant on observations from amateur astronomers to tell us what they are - or are not - seeing.

As always, the amateur astronomers have come through for us, but the news is bleak. The image we feature this week was recorded by Lorenzo Comolli (Tradate, Italy) on December 11th, 2013, and shows a beautifully star-filled but depressingly comet-free field of view, at the center of which lies the location that comet ISON's orbit predicts it would be on this date. We see nothing comet-like in this image, while stars as faint as magnitude +17 are visible - that's on the order of ten thousand times fainter than we would have needed comet ISON to be in order to be naked eye visible.

Lorenzo is not alone in his observations as numerous other astronomers such as Alan Hale (of Hale-Bopp fame) also came up empty handed. Many of our remaining hopes now reside with the ultra-powerful Hubble Space Telescope, which is due to attempt observations in the coming few days. However, while Hubble has the ability to see incredibly faint objects, it also has an extremely narrow field of view, meaning that they will have to get very lucky and point directly at any remaining chunks... if there are indeed any left at all! We will of course report back on this website as to the successes of the Hubble observations.

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 sungrazer@nrl.navy.mil, 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!