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NASA’s Deep Impact eyes comet ISON

NASA’s Deep Impact spacecraft has acquired its first images of comet C/2012 S1 (ISON). The images were taken by the spacecraft’s Medium-Resolution Imager over a 36-hour period on Jan. 17 and 18, 2013, from a distance of 493 million miles (793 million kilometers). Many scientists anticipate a bright future for comet ISON; the spaceborne conglomeration of dust and ice may put on quite a show as it passes through the inner solar system this fall.

"This is the fourth comet on which we have performed science observations and the farthest point from Earth from which we’ve tried to transmit data on a comet," said Tim Larson, project manager for the Deep Impact spacecraft at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. "The distance limits our bandwidth, so it’s a little like communicating through a modem after being used to DSL. But we’re going to coordinate our science collection and playback so we maximize our return on this potentially spectacular comet."

Deep Impact has executed close flybys of two comets — Tempel 1 and Hartley 2 — and performed scientific observations on two more — comet Garradd and now ISON. The ISON imaging campaign is expected to yield infrared data, and light curves (which are used in defining the comet’s rotation rate) in addition to visible-light images. A movie of comet ISON was generated from initial data acquired during this campaign. Preliminary results indicate that although the comet is still in the outer solar system, more than 474 million miles (763 million kilometers) from the sun, it is already active. As of Jan. 18, the tail extending from ISON’s nucleus was already more than 40,000 miles (64,400 kilometers) long.

Long-period comets like ISON are thought to arrive from the solar system’s Oort cloud, a giant spherical cloud of icy bodies surrounding our solar system so far away its outer edge is about a third of the way to the nearest star (other than our sun). Every once in a while, one of these loose conglomerations of ice, rock, dust and organic compounds is disturbed out of its established orbit in the Oort cloud by a passing star or the combined gravitational effects of the stars in the Milky Way galaxy. With these gravitational nudges, so begins a comet’s eons-long, arching plunge toward the inner solar system.

ISON was discovered on Sept. 21, 2012, by two Russian astronomers using the International Scientific Optical Network’s 16-inch (40-centimeter) telescope near Kislovodsk. NASA’s Near-Earth Object Program Office, based at JPL, has plotted its orbit and determined that the comet is more than likely making it first-ever sweep through the inner solar system. Having not come this way before means the comet’s pristine surface has a higher probability of being laden with volatile material just spoiling for some of the sun’s energy to heat it up and help it escape. With the exodus of these clean ices could come a boatload of dust, held in check since the beginnings of our solar system. This released gas and dust is what is seen on Earth as comprising a comet’s atmosphere (coma) and tail.

ISON will not be a threat to Earth — getting no closer to Earth than about 40 million miles on Dec. 26, 2013. But stargazers will have an opportunity to view the comet’s head and tail before and after its closest approach to the sun — if the comet doesn’t fade early or break up before reaching the sun.

The Evaporating Atmosphere of HD 189733 b

A Jupiter-size planet around a distant star has given astronomers a rare glimpse into the effects of space weather beyond our solar system: a view of an alien world unleashing an intense plume of gas triggered by an eruption from its parent star.

HD 189733b is a gas giant planet similar to Jupiter, but orbits extremely close to its star, just one-thirtieth of the distance between Earth and the sun. While the parent star, named HD 189733A, is slightly smaller and cooler than the sun, the climate of the alien world is still exceptionally hot, with temperatures above 1,830 degrees Fahrenheit (1,000 degrees Celsius).

The exoplanet’s close proximity to its star also means its upper atmosphere is constantly battered by energetic extreme-ultraviolet and X-ray radiation. According to the researchers, this makes HD 189733b a fascinating place to study how stellar activity affects an alien planet’s atmosphere.

Despite HD 189733b’s extreme climate, the atmosphere alone is not hot enough to evaporate at such a staggering rate. Rather, the evaporation is thought to be caused by powerful doses of X-ray and extreme-ultraviolet radiation from the parent star. Based on their calculations, the star’s eruptions are 20 times more powerful than those on the sun, and HD 189733b likely receives 3 million times more X-ray radiation than Earth.