Comet ISON's Current Status

Latest Update: November 19th, 2013



The latest light-curve for Comet ISON (compiled November 19, 2013 by Matthew Knight).
Yesterday we discussed, among other things, whether or not comet ISON had fragmented. This story caught the attention of lots of media and news outlets, so several of us have had a busy day or so responding to queries. The takeaway message from yesterday was simply that "we don't know... but we suspect it's still in one piece. Today we still don't know if the comet is in one piece, but the evidence is implying that it is.

Comet ISON is getting difficult to observe: it's low to the horizon in brightening skies, and a full moon is certainly not helping. But images are still coming in, and in shots like this one from Indonesia last night, the comet's nucleus still looks nicely condensed and symmetrical.

There had been reports of "coma wings" in processed images of the comet, and these are a feature that has been associated with fragmentation of comet nuclei. We blogged about this yesterday with the main conclusion being that yes it certainly could mean fragmentation, but also could mean one of several other things that have nothing to do with fragmentation. Thus we urged continued imaging and community-wide discussion of this feature. Overnight we have heard that those "coma wing" features appear to have faded. Does this mean ISON has definitely not fragmented? No, but it lends weight to the belief that it's still in one piece.

Again we emphasize here that we applaud the group for publicly making those statements and distributing the observations. This is how the best science happens, when we share, discuss, cooperate and coordinate! We encourage all other observing groups to take the same approach with their data and keep the discussion rolling. And speaking of which...

This is the most exciting news of the day: the scientists using the European Southern Observatory's TRAPPIST telescope are this morning reporting that comet ISON is again in outburst! Overnight they have seen a six-times increase in production rates (gases, water). This is not as large as the outburst last week that saw a ten-or-more-fold increase in production, but this is still a very significant outburst. They note that they are just about at the end of their observing run but will continue to follow up as much as they can. Both those scientists and indeed the CIOC are urging observers to try and image the comet when at all possible. We really are down to the wire with pre-perihelion observations!

Finally, Matthew has updated our light-curve today, which you can see above. The post-outburst observations are very evident but note that there are no new observations that include the second outburst we just detailed above. It will be a day or so before that information comes in. Furthermore, data points are going to be scarce now for all the reasons we just highlighted about how difficult ISON is becoming to observe. We are almost in the domain of the solar spacecraft only...

So for those short on time, today's tl;dr is that ISON still appears to be in one piece, but is undergoing a new outburst right now. Observing conditions are becoming extremely difficult, and very few pre-perihelion days remain for useful ground-based observations.

Light-Curve

Frequent visitors to this page will notice that the above lightcurve plot has been overhauled. It is now a bit busier, but is also conveying more information and is hopefully easier to see exactly what’s going on right now. In a nutshell, here is what is new.

First, we are now plotting two sources of data. The first, shown as red circles, are the magnitude measurements being reported by the Minor Planet Center. As we’ve discussed before, these measurements vary widely from observer to observer based on each person’s technique and instrumentation. Most are only measuring a relatively small region near the comet, yielding a fainter brightness than if they measured the whole coma.

The second, plotted as blue triangles, are from the International Comet Quarterly (thanks to Alexandre Amorim for pointing this out to us). These data had not previously been plotted here, but are quite useful. The ICQ data are “total magnitude” estimates that try to encompass all of the light from the comet. Many of these estimates are made by very experienced observers using binoculars or even (soon) their naked eye who compare the comet to nearby stars of known brightness. It takes a lot of work to be good at this technique, but as you can see from the relatively small scatter in the blue points, yields quite reliable estimates.

You will notice that the ICQ data fall much closer to the trend line we’ve been plotting all along, but back in the first half of 2013, the red and blue points roughly overlap. This is because back then Comet ISON had a small angular size, so in effect all brightness measurements were “total” measurements. Now that ISON is much closer to the Sun, its coma is much larger in an absolute sense. Furthermore, it is also closer to the Earth, so its apparent size is also larger. The result is that what worked very well early on (measurements using a small aperture on a CCD) has begun to diverge systematically from the total brightness. So now the blue points do a better job answering what everyone cares about: “How bright is Comet ISON?

The other big change we’ve made is to create a smaller, zoomed in plot that only shows the most recent data. This gives a much better idea of how closely the current estimates are following the trend line. The immediate takeaway is that the huge brightness increase over the last few days isn’t that surprising, and we can probably hope to see similar brightness gains on a daily basis over the next two weeks (assuming ISON hasn’t broken up)!

It will, of course, become harder for people to estimate the brightness as ISON gets closer to the Sun because the sky will get brighter when ISON is observed, and will therefore be harder to detect the full coma or to compare it to nearby stars. At some point we will likely stopping getting new ground-based brightness estimates and will have to start relying on observations from the SOHO and STEREO spacecraft. But rest assured, we will plot data here as frequently as we can, so please keep checking back.

Now we're around perihelion time for ISON, we will update this "Current Status" page more frequently -- in some cases daily. Check back regularly for updates, and follow the CIOC's Karl Battams '@SungrazerComets' Twitter feed.

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