Comet ISON

A sungrazer zooming our way

comet ison
This contrast-enhanced image of Comet ISON, taken by the Hubble Space Telescope on April 10, 2013, shows dust particle release on the sunward-facing side of the comet's nucleus, the small, solid body at its core. The image was taken in visible light with Hubble's Wide Field Camera 3. Blue false color was added to bring out details in the comet structure. Image: NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team

April 28, 2013 - NASA's Hubble Telescope is providing a clear view of Comet ISON, a newly-discovered sungrazer that will brighten our sky later this year -- IF, that is, it manages to remain intact as it squeezes past the Sun. It's offering a rare opportunity to follow a comet on a first-ever pass through the inner solar system.

Like all comets, ISON is a clump of frozen gases mixed with dust -- a dirty snowball -- shooting down a long, narrow orbit toward the Sun. On November 28 it will come within just 700,000 miles of the Sun, so close and so hot that it may vaporize in the strong evaporation and tidal forces that often lead to the fragmentation of sungrazing comets. The most famous comets of this type are the Kreutz Sungrazers, which all arose from a single giant comet that shattered into many smaller ones during its first passage through the inner solar system. Some speculate that an extremely brilliant comet seen by Aristotle in 371 BC was, in fact, this mega-comet parent.

The image at right was made a little more than two weeks ago, when ISON was barely within the orbit of Jupiter. Like other comets, ISON will become more brilliant as it nears the inner solar system, where the Sun's heat will evaporate its ices into jets of gases and dust. But ISON is already becoming active, with a bright jet -- dust particles shimmering with reflected sunlight -- blasting off its nucleus. As these dust particles shimmer in reflected sunlight, a portion of the comet's tail becomes visible in the Hubble image. Some scientists think that if it clears the Sun, this comet will eventually become as bright in our sky as a full moon.

Next week, University of Maryland-led research team will be using Hubble to gather information about ISON's gases. "We want to look for the ratio of the three dominant ices, water, frozen carbon monoxide, and frozen carbon dioxide, or dry ice," said Maryland astronomy professor Michael A'Hearn. "That can tell us the temperature at which the comet formed, and with that temperature, we can then say where in the solar system it formed."

The team will use both Hubble and the instruments on the Deep Impact space craft to go on following ISON as it travels toward its November close encounter with the sun.

Based on materials obtained from AAAS

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