The Comet is Closing In on the Inner Solar System
This is shaping up to be a great year for comets. Comets 2012 F6 Lemmon and C/2011 L4 PANSTARRS have graced the skies, and now we have C/2012 S1 ISON rushing in for a lap around the Sun later this year. Astronomers have been keeping an eye on it for some months, and today Hubble Space Telescope released a picture of the comet taken on April 10. At that point it was slightly closer than Jupiter is from the Sun.
What’s interesting about this image is the level of activity this comet is showing and it’s not all that close to the Sun. It’s sprouted a dust tail as its ices sublimate and carry material away on the solar wind. Right now astronomers are studying the many images (such as this one) from observations of ISON to calculate the size of its nucleus and determine some other features of the comet. For example, the Hubble image reveals a strong jet blasting dust from the part of the nucleus facing toward the Sun.
Taking spectral observations of the comet over the next months (that is, studying the light from it) will also help comet scientists determine the composition of the nucleus — that is, the types and amounts of ices and dust that are mixed up in the frozen nucleus.
When Comet ISON rounds the Sun (it will be closest to the Sun on November 28th, 2013), it promises to be bright and extensive. How much remains to be determined. We just have to wait as it gets closer and brighter so we can see for ourselves. But, if it’s anything like Hale-Bopp or Hyakutake were in 1996 and 1997, we could be in for a very lovely sight in our nighttime skies later this year. I remain hopeful that it will be spectacular, which is why I’ll be anxiously awaiting reports from astronomers as ISON gets closer and closer!
Interestingly many ISON observers in the amateur community see this comet severely underperform in recent months, with the coma brightness and diameter stalling; some have all but given up hope for a great show. And even the brightness model used by the central ephemeris service of the JPL has been toned way down.
In other news this HST image had ‘leaked’ already 10 days ago when someone went through the space telescope’s observing log and discoverd the raw image file just after it was taken: I think this is a first in 23 years of HST history.
Daniel, that’s why I’m “hedging my bets” about ISON’s brightness. If it turns out to be a performer like Hale-Bopp, then we’ll have quite a show on our hands! I think that as it moves within the orbit of Mars, etc. we’ll have a much better indication of how it’s going to look.
I had heard rumors about the “hacking” of the Hubble image — this is very reminiscent of another incident where someone spied on someone else’s observing logs and then tried to make a “discovery” out of their finding.