The Flight of Comet ISON

The folks at the Solar and Heliospheric Observatory (SOHO) have been busy on this Thanksgiving Day taking images of ISON’s flight around the Sun. While we had hoped ISON might survive its closest approach, the truth is that a sungrazing comet’s chance of surviving a trip around the Sun is remarkably similar to that of a snowball in hell.

Even so, the results are quite surprising. Take a close look at the last few frames of the video:

Comet ISON captured by SOHO on November 26 – 29, 2013 – Update 9

Let me explain the video a bit: The Sun is at the very center of the image, but in order for SOHO to take images of its outer heliosphere, it must block out the Sun itself. The Sun’s disk is drawn in white so we can tell exactly where it is, but the occulting disk needs to be considerably larger than the Sun itself in order to block out its light.

ISON enters the field of view in the lower right, peaking in brightness at around 0:10 (the horizontal line it produces is not real – it’s an artifact due to the detector saturating, a process called blooming).

ISON starts to dim as it goes “under” the occulting disk, and that’s typically an indication that the comet is breaking up. But then something appears to emerge from underneath the disk, and it’s pretty damn bright!

Woah! Image credit: NASA/ESA/SOHO
Woah! Image credit: NASA/ESA/SOHO

In the updated image taken at 12:30 UTC on November 29, the object has moved farther away and continues to appear rather comet-like:

Even more woah! Updated SOHO image taken Nov 29, 12:30 UTC
Even more woah! Updated SOHO image taken Nov 29, 12:30 UTC

Here’s another view of the event, taken with SOHO’s LASCO C2 instrument, which has a close-in field of view:

All of this is to say…I have no idea. Comets are very strange creatures, and they surprise us all the time. At this point, I can hardly make any conclusions, and from what I’m reading on the interwebs even comet specialists are stumped. And that’s the best part of all of this. Being surprised by nature is part of what makes science so fun!

ISON may very well be the little comet that could.

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