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Comet ISON's Current Status
Latest Update: November 13th, 2013
our last update, and it seems that something different might be going on with comet ISON. On the "comets-ml" chat group, Emmanual Jehin from the University of Liege is reporting an outburst in comet ISON, resulting in production rates that are double that of what they were a day earlier. (The term "production rate" refers to the amount of different materials such as H2O, CO2, etc, that are being released from the comet's surface.
There have been reports of it brightening by an order of magnitude, and recent images are showing really nice structures in the comet's tail. Some of those could be from outbursts or jets, but more likely we are beginning to see the interaction with the solar wind that we blogged about a couple of weeks ago. That interaction is really quite evident in this image, where it seems quite obvious we have a small "disconnection event" in the tail. (These are common: read that blog post.)
It's far too early to draw any conclusions here. Aside from the result from the Belgian group the reports are somewhat anecdotal and until we get more data from scientific instrumentation, then we can't get ahead of ourselves. But it does sound like something is happening, and that could be one of a couple of things.
One of the long-standing "criticisms" of ISON is that it has not brightened as much, or as rapidly, as people thought it would and should and has exhibited a rather flat behavior. It could be that the comet is now simply finally "turning on". After all, it is now only 0.66AU (61,000,000mi, 99,000,000km) from the Sun, and if it is to reach the low negative magnitudes at perihelion we've always thought it would then it needs to start brightening by an order or two magnitudes within the next week. So this could be really great news, and indicate that we are indeed going to have a nice bright comet in our solar spacecraft images in a couple of weeks time!
On the flip-side, this reported outburst could be bad news. The nucleus may have disrupted or fragmented, or a large fracture appear in the surface leading to a massive outpouring of volatiles. If so, the comet will likely brighten very rapidly over the next few days with a increasingly large dusty coma surrounding it and then begin to fade. Quite possibly it would simply fade out altogether in this situation, though some comets do outburst and then return to more normal levels.
If it's not already obvious... we have no idea what ISON is doing right now, or what it will do in the next couple of weeks! We simply urge everyone who can to get out an observe it while they can. Twilight is beginning to encroach, and your pre-perihelion observing window is getting really short.
To end on a high note, here's another jaw-dropping image from Michael Jaeger.
So today's tl;dr is this: Fifteen days from perihelion, Comet ISON is brightening fast, is interacting with the solar wind, and appears to be undergoing an outburst. This could be really good or really bad. Get out there now and view it while you definitely still can!
Light-CurveAbove is the latest "light-curve" we have for comet ISON, based upon data submitted by astronomers to the Minor Planet Center. This plot was created by the CIOC's Matthew Knight. There are a couple of important features to note:
1. You will notice that the peak of this plot is not shown. Why? Because it's meaningless. It is extremely difficult to accurately predict the peak brightness of almost any comet, but this is particularly the case the closer a comet approaches to the Sun. ISON is a Sungrazing comet, following an orbit that will take it through the Sun's extended outer atmosphere ("corona"). During this period it will experience intense bombardment of solar radiation and its surface will sublimate (turn directly from solid to gas) at an almost alarming rate. In addition, it will experience extreme structural stresses from the Sun's enormous gravitational pull. These factors lead sungrazers in particular to behave very unpredictably, and we can only guess at how bright it will be, or even if it will survive. That said, we on the CIOC Team have for many months now held to our opinion that ISON's peak brightness (which will occur in the few hours surrounding perihelion) could be anywhere from magnitude -7 to +5 or more, though our educated guesses are hovering around -3 to -5.
2. The black line in this plot is a simplified model of the predicted trend of ISON's brightness. It is not a line that is fitted to the data, nor is it a line to which the data should aspire. You can almost consider this as two different plots that share an axis: a possible model of ISON's brightness (in this case, we use JPL's model parameters), and the reported observations from ground observers.
3. The large spread in magnitudes reported by observers is not a surprise. Viewing conditions differ for all observers, as does the skill level of the observer, the quality and type of instrumentation they use, the kinds of filters they use, and their method for estimating the brightness. It is very common to see such a divergence in reported values (comet Hale-Bopp is a great example.)
If you browse around online you will easily find references to estimates of magnitude -10 or even -15, and the term "Comet of the Century" has been tossed around with abandon. Those are not the words or the opinion of the CIOC Team, and while they may perhaps turn out to be true, we think it extremely unlikely. Likewise, reports of its imminent demise are completely unfounded, and while they may prove to be true, they are currently based on speculation and selective interpretation of data. More likely, ISON should turn out to be one of the brighter comets in the past several years and, thanks to the global astronomy community, we hope one of the most broadly observed comets in history!
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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