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April 05, 2016

New comet bears Rochester scientist’s name

observatory
The Cerro Tololo Inter-American Observatory in Chile (below) houses the Dark Energy Camera (DECam) on the Blanco 4-m telescope, from which images are being collected and analyzed by Eric Mamajek’s research group.

A Rochester scientist has discovered a new comet—the first to be discovered by an astronomer associated with the University or the Rochester area in over a century, his colleagues believe.

David Cameron, a visiting scientist in Eric Mamajek’s research group in the Department of Physics and Astronomy, discovered the short-period comet, named Comet P/2015 PD229 (ISON-Cameron).

Cameron spotted the comet last August while analyzing images taken in May 2015 by Mamajek with the Dark Energy Camera (DECam) on the Blanco 4-m telescope at the Cerro Tololo Inter-American Observatory in Chile.

“We were looking not for comets but objects in the outer solar system called Kuiper Belt objects, which orbit the sun far beyond the orbit of Neptune,” Cameron says. “The former planet Pluto is the most well known Kuiper Belt object. In our images, these objects appear as little dots of light that, over time, seem to slowly jump from point to point. While searching our images one day, I was surprised to find a small streak of light with a tail, and like the Kuiper Belt objects, it also jumped from point to point over time. The object wasn’t described in any database, so that was it: an unexpected new comet discovery.”

Mamajek’s group has been using DECam to discover both faint young failed stars (“brown dwarfs”) in nearby star clusters, a project led by PhD student Fred Moolekamp, and new outer solar system objects, led by Cameron.

“Discovering a comet is not as rare nowadays but still exciting,” says Mamajek, associate professor of physics and astronomy. “About 90 comets of all types were discovered last year. This is one of about 500 Jupiter family comets, which means that Jupiter strongly influences its orbit around the sun.

Though no comets have been found by Rochester astronomers over the past century, Rochester does have a history of comet hunting. “The prolific 19th-century comet hunter Lewis Swift discovered or codiscovered 13 comets, including the famous comet 109P/Swift-Tuttle—the parent body of the Perseid meteor shower,” Mamajek says.

Swift (1820–1913) was born in the village of Clarkson in Monroe County and, in recognition of his astronomical discoveries, received an honorary degree from the University in 1879.

Mamajek explained that the new comet appears to be about 13 miles across, “larger than most other Jupiter-family comets.” It orbits the sun every 19.2 years, mostly between the orbits of Jupiter and Saturn. The comet reached its closest point to the sun in August 2015 just inside the orbit of Jupiter. Given their icy natures, low inclinations, and orbits crossing the large outer planets, it is thought that Jupiter-family comets originate from the Kuiper Belt beyond Neptune. When their orbits bring them closer to the sun, the resultant heating causes their volatile compounds, including water, to sublimate off and produce a distinctive tail.

More information about the comet is online at pas.rochester.edu/~emamajek/DECAM/COMET1.

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