Recent photos taken by the Hubble Space Telescope show that Comet ISON remains in one piece as it plunges ever closer to the sun. That’s good news. Had the nucleus broken into pieces, Hubble would have seen evidence for multiple fragments. While a splitting comet makes for fascinating observing it also spell its end. Each fragment fizzes away leaving a tail without a head.
We don’t want to happen to Comet ISON. It would mean the end of our hopes for a great show after it passes closest to the sun on November 28.
One change we CAN see in the Hubble photos is the disappearance of a bright jet of material streaming away from the nucleus. This fountain-like feature results from fresh ices, which contain dust and other materials, vaporizing from fissures or cracks in the icy body of the comet. Sunlight heats ice below the surface to form gas-filled cavities under pressure. When the gas finds a vent or passage to the surface, it erupts in a jet of material similar to air rushing from a balloon.
Comparing the two Hubble pictures we can see that the dust jet’s gone – perhaps it turned off temporarily. Photos taken by amateur astronomers, which have a much larger field of view than the Hubble, show an ever-lengthening tail. All these changes make watching comets a lot of fun.
At present, Comet ISON is still near Mars in the morning sky before dawn. Moonlight will compromise our view of the 10th magnitude “fuzzy glow” for about another week. Speaking of Mars, mission controllers attempted to photograph ISON with the Mars Opportunity Rover during its flyby earlier this month, but the comet was too faint to show in the rover’s panoramic camera. I still haven’t heard whether the Curiosity rover had better luck.
Meanwhile, just a day ago, the obscure 14th magnitude comet C/2012 X1 (LINEAR) suddenly brightened some 150 times times to 8.5 magnitude.
Here’s a object very few people were paying attention to that’s now bright enough to spot in binoculars under a dark sky. The sudden flare may originate from a massive buildup of gas inside the comet that fractured and broke off a good-sized chunk of comet crust.
Something similar happened to Comet Holmes in October 2007 when it brightened over half a million times from magnitude 17 to 2.8 over the space of only 42 hours. C/2012 X1 currently shines in Coma Berenices low in the dawn sky. It’s about 2′-3′ arc minutes across (less than 1/10 the diameter of the full moon) with a small, bright core. I’ve included a general finder map that shows the comet’s position and stars down to about 6th magnitude.
If X1 remains relatively bright, we’ll soon have four comets viewable in small telescopes by early November – Encke, ISON, Lovejoy and X1 LINEAR!