Experiencing Kitt Peaks and Valleys as ISON Takes Us On A Ride


The McMath-Pierce Solar Telescope at Kitt Peak National Observatory on the morning on November 26, 2013. [Image credit: Karl Battams]
I arrived at Kitt Peak fairly late last night and immediately fell into a chaotic mess of emails, media requests and - most importantly - comet ISON data! I'm sitting side-by-side with fellow CIOC-er Matthew Knight, and working with him on analyzing the solar spacecraft data as it comes in. In particular, he has been looking at the brightness of the comet ("photometry"), as that can be a good indicator of what's going on with it.

Yesterday the big news was that ISON was giving some serious indications of having "disrupted" - i.e. an indication that its nucleus had simply fallen apart. Let me explain what that would mean. If you imaging a comet as big brick house, the bricks would be the dust/rocks in ISON's nucleus and the mortar that holds the bricks together would be the comet's ice. In essence, the ice is the structure that binds the whole comet together, and as that ice begins to melt away, the rocks/dust (our bricks) become loose and fall away, exposing fresh bricks and mortar. This complete disruption we speak of would mean that the majority of the ices (the mortar) has melted and the dust/rocks (bricks) are completely loose.
So what would that mean? Well, it would mean that comet ISON is now more-or-less just a giant cloud of disconnected dust and rapidly melting chunks of ice. If this is the case, then when ISON passes through the NASA SDO field of view and the Sun's million degree solar corona, the likely outcome would be the complete vaporization of the comet. Scientifically, and visually in those images, this would likely be spectacular, but for those that want to see ISON in the night sky in December it would be catastrophic news.

But is that what has happened?

Matthew and I talked extensively about this last night, and as he performed his photometry and observed the comet's brightness dropping, he said something along the lines of "I hate to say it, but I really think it's gone." That was a pretty heartbreaking admission for him, and even more so for me as I reluctantly had to agree. This would not spell the end for science - far from it, in fact! But would definitely kill the chances of a nice night sky object in December. And so it was with heavy hearts and heavier eyelids that we retreated to our dorm rooms for the night.


The CIOC's Matthew Knight busy at work analyzing STEREO data in the solar telescope control room at Kitt Peak National Observatory [Image credit: Karl Battams]
This morning was a fresh day, and we came in to the telescope control room to a fresh set of STEREO data waiting for us on our laptops. Having left Matthew to do his photometry while I analyzed some other interesting aspects of the data I'd spotted, I was started out of my science-induced stupor by an exclamation of, "It got brighter again!/. Not quite believing him, I scooted my chair over and sure enough there was a lightcurve showing a nice steady increase in ISON's brightness! What gives??!

First the good news: we are now significantly less fearful that it has fully disrupted, and we think there is still a significant chance that an appreciable chunk of nucleus still exists! Now the details: why do we think this, and what do we think might have happened?

When we look at Matthew's light-curve (sorry, we can't show it here right now) we see that shortly after ISON entered the STEREO field of view, the brightness increased sharply and then leveled off. This corresponds in time with the reported increased in dust and decrease in emission. The brightness then fell, which was very worrying. That's what led us to our "demise" conclusion. But then over the following ~36hrs, to at least 12UT on Nov 26, ISON's brightness climbed gradually and steadily, more-or-less exactly how we expect a healthy sungrazer to behave! So our hypothesis is that ISON may have simply undergone another outburst, perhaps involving some degree of fragmentation, but has now returned to "correct" behavior.


Comet ISON has entered the field of view of the LASCO C3 coronagraph telescope on the ESA/NASA SOHO satellite.[Credit: ESA/NASA]
We don't know if that's true, or if ISON really has just fallen apart. And we still have no idea what ISON will do at perihelion. But we don't have too much longer to speculate! Just a short time ago, comet ISON entered the SOHO/LASCO C3 field of view, giving us our first true realtime look at the comet!

At first glance, I had to exclaim that ISON looks remarkably similar to how comet C/2011 W3 (Lovejoy) did in 2011 when it first entered LASCO C3 in December 2011. This would not be the first time we've used Lovejoy as an analogy, though that comet had nowhere the quantity of pre-perihelion observations that ISON has had, so we can't easily compare the two.

Upon inspection I'd say that ISON is maybe marginally fainter than Lovejoy was at this point, but really not by much. Matthew will be looking at that soon and we'll let you know the outcome. And we know all too well that Sungrazing comets can brighten by anywhere up to ten magnitudes as they cross this field of view. So all is far from lost, and while yesterday ended on a sour note, today ends on a much better one. We still have a comet, and tomorrow could be a really exciting day as it moves through this field of view and also the two COR-2 cameras on the twin NASA STEREO satellites.
You should definitely bookmark the SOHO latest images page and check back often as we have pretty much realtime coverage throughout perihelion now. On Thursday, the focus will be on the LASCO C2 camera and then, perhaps most exciting of all, the NASA SDO cameras. The SDO team will be holding a live viewing party that you really shouldn't miss! There will also be a Google Hangout from 1:00 to 3:30pm EST featuring Alex Young and Dean Pesnell from NASA Goddard, astronomy blogger extraordinaire Phil Plait, and me! It'll be a really fun event so we urge you to watch us live on Youtube (I don't think the link has been released yet) and Tweet us your questions with the tags #ISON and #AskNASA.

Keep up-to-date on the latest ISON and sungrazing comet news via my @SungrazerComets Twitter feed. All opinions stated on there, and in my blog posts, are my own.