Comet Hergenrother photographed last night (Oct. 25) with the 79-inch telescope by a team of amateur astronomers. The fuzzy fragment is snugged right up against the icy-dusty core of the comet called the nucleus. A coma of  dust and gases surrounds the nucleus. Credit: E.Guido/N.Howes/G.Sostero/LCOGT/Faulkes Telescope

Astronomers have been watching Comet 168P/Hergenrother closely the past couple months since it’s been in outburst and much brighter than expected. There have also been recent reports of fragmentation of the comet’s nucleus.

Heat from the sun causes comet ices to vaporize; the expanding gas can stress a comet’s fragile, icy nucleus, riddling its outer crust with fissures. As fresh ice is exposed, more gas and dust jet outward from the nucleus to swell the comet’s coma or temporary atmosphere. It all adds up to a surge in brightness that can make an otherwise obscure comet brighten enough to see in even a small telescope.

4x closeup of the comet’s nucleus shows the fragment very clearly.  Click image to see a nice animation. Credit: E.Guido/N.Howes/G.Sostero/LCOGT/Faulkes Telescope

Several photos have been published that may or may not show pieces leaving the nucleus and drifting down the comet’s tail, but the first unequivocal image was released today by a team of amateur astronomers at the Remanzacco Observatory in Italy. The fragment pictured in the photos might be a clue to the comet’s steep rise in brightness that began in late September.

Jets of carbon dioxide gas expel gas and hunks of snow – some as big as basketballs – from the nucleus of Comet Hartley 2 in this photo taken by the EPOXI spacecraft during its November 2010 flyby. Click to see a video. Credit: NASA

Nick Howes, Ernesto Guido and Giovanni Sostero took numerous exposures using a 79-inch (2.0-meter) telescope in Hawaii. They operated the scope remotely, downloaded the images and processed them to reveal a glowing fragment just south of the bright nucleus. This “chip off the old block” may fragment further and possibly kick up Hergenrother’s brightness another notch. We’ll have to wait and see.

Fragment B in Comet Schwassmann-Wachmann 1 fragments further into a clouds of mini-comets as it moves down the main comet’s tail. The photo was taken by the Hubble Space Telescope in April 2006. Credit: NASA / ESA

Amateur astronomers with 8-inch or larger telescopes will want to study the comet closely with their highest magnifications that atmospheric seeing (steadiness of the air) will allow in the coming nights. The fragment’s a mere 2 arc seconds across and faint, but there’s a chance it may brighten further and separate from the nucleus, making it easier to spot.

Comet nuclei are delicate creatures subject to fractures and breakups especially when they approach the sun. One of the best examples of a fragmenting comet is 73P/Schwassmann-Wachmann 1. The Hubble image at left shows the break-up best, but fragments could even be seen in amateur instruments.

Another possible clod of dust/ice directly behind the comet’s nucleus on Oct. 24, 2012. Credit: Dr. P. Clay Sherrod of the Arkansas Sky Observatories. Click photo to visit his site.

Hergenrother is receding back into the depths of space, having passed Earth earlier this fall, but it’s still bright enough for scopes 6-inches and up. To keep eyes on the comet, click HERE for a map and more info.