Comet ISON's Current Status

Latest Update: November 8th, 2013



The latest light-curve for Comet ISON (compiled November 04, 2013 by Matthew Knight).
As of this morning, comet C/2012 S1 (ISON) was 0.8AU (74-million miles, 120-million kilometers) from the Sun, and zooming along at 47km/s (105,000mph, 169,000kph). By Monday evening it will be inside of Venus' orbit (not physically near Venus, though). We now only have 20-days until ISON reaches perihelion, at around 18:36UT on November 28, 2013, but we still don't know if it will reach there and - if it does - how long it will last!

In our previous update to this page we commented on a mixed bag of data that heralded both good and bad signs for comet ISON, and raised many questions. Is its dust production rate flattening out, or even tapering off? Or is it dramatically increasing? Or perhaps increasing but not at the rate we'd expect from a comet so close to the Sun already? The comet is clearly still in one piece as of a few hours ago, but how long will that last? Days? Weeks? Indefinitely?

All of these are valid questions, and depending on who you ask, you will get a slightly different response.

Comet ISON is being a particularly odd comet, but this is a good thing! We always felt it would be an interesting object, hence this high-profile observing campaign, and that hunch is paying off. We have an unprecedented array of telescopes pointing at this dynamically new comet, and when the show is finally over (whenever that may be), we will begin to put the pieces together and gain a very complete understanding of this object. Again we urge everyone to read Matthew's latest blog post about what we might expect over the next couple of weeks.

Today there are two results we'll highlight very quickly. The first is one that we mentioned already - namely that the Chandra X-ray telescope made some successful and very interesting detections of comet ISON in EUV and soft x-ray wavelengths. Those observations were spearheaded by the CIOC Chair Casey Lisse (who actually first discovered X-ray emission from comets), and they will absolutely be detailed on this website in the coming days. The other really nice result is yet another jaw-dropping image of comet ISON by astrophotographer Damian Peach. This one is particularly nice as it very clearly shows the new structure in ISON's tail that we recently mentioned. This new feature, which you can see as a fork (actually two forks...) below the main dust tail, is an ion, or gas, tail. We see these all the time in comets, and they are a consequence of solar ultraviolet photons stripping electrons off of the neutral gas that has been released from the comet via a process we call ionization. As ISON gets closer to the Sun, we hope to see some interesting interactions between its tails and the solar wind.

So the bottom line for today is that ISON is still there, still in one piece, and still becoming increasingly visible to observers with binoculars and small telescopes. It's not naked eye, however, and at this point probably won't be before perihelion as it's going to get to close to twilight skies now. Will it be naked eye in December, after perihelion? Maybe...

Light-Curve

Above 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 for more CIOC, ISON and comet news.

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