|A NASA time-lapse image of Comet ISON before and after its closest encounter with the Sun on November 28, 2013, assembled from images taken by the NASA/ESA SOHO spacecraft.|
At the moment Comet ISON made its closest passage to the Sun last week, an interviewer asked me on a radio show exactly when we would know whether ISON had survived its encounter with the Sun.
Up to that time, it appeared that ISON would either disappear near the Sun or survive to become the long heralded 'Comet of the Century' once it came closer to the Earth in December. I had not anticipated the interviewer's question about timing, and I responded that we could expect to have some idea of ISON's fate that evening, some hours after the interview.
Barely an hour later, I began to see tweets proclaiming the end of ISON. The news was disappointing not only because it meant that there would be no more opportunities to see ISON, but also because I had given an incorrect answer about when we would know what happened to the comet.
But as the hours went by, new images from SOHO and other space-based cameras revealed that ISON had reappeared, albeit in a severely reduced form. In the days since then, ISON has been fading away again. As Phil Plait said in his Bad Astronomy blog, it's been one surprise after another from ISON, and we are all wondering if there are more surprises in store.
If there is one thing that's been consistent about the discoveries we have made about our solar system in recent decades, it is that they defy expectations. This is doubly true when it comes to comets. Comet Kohoutek fell far short of expectations 40 years ago, but we also have memories of the dramatic collision of the fragments of Comet Shoemaker-Levy 9 with Jupiter in 1994.
Even if ISON does indeed disappear, it has already provided plenty of fodder for researchers. That's the one thing that was true a week ago as it is today.
It turns out that we didn't get the full answer on ISON's survival when I thought we would. We may still not have that answer. Comet ISON has given us a good reminder to avoid the temptations of instant science.