Hubble images distant comet beyond Saturn's orbit

Comet that originated in Oort Cloud has likely been active for at least four years.
By Laurel Kornfeld | Oct 02, 2017
NASA's Hubble Space Telescope has imaged the most distant comet ever located, an object that likely originated in the Oort Cloud and is now headed on its first ever journey toward the Sun.

Titled Comet C/2017 K2 (PanSTARRS), the comet was found and photographed by Hubble approximately 1.5 billion miles from the Sun, just beyond the orbit of Saturn.

It was first spotted by the Panoramic Survey Telescope and Rapid Response System (PanSTARRS), a wide-field astronomical imaging system at the University of Hawaii, in May of this year.

Based on its orbit, scientists believe the comet came from the Oort Cloud, a spherical region with a diameter of almost one light year that surrounds the solar system and contains hundreds of billions of comets.

Nicknamed K2, the comet has likely been traveling toward the inner solar system for millions of years.

Since leaving the Oort Cloud, which has an average temperature of minus 440 degrees Fahrenheit, K2 has warmed on approach to the Sun, causing it to develop an 80,000-mile-wide coma or central cloud of dust surrounding a solid 12-mile-wide nucleus composed of frozen dust and gas.

Like all Oort Cloud objects, K2's composition is much like that of objects in the solar system's earliest days.

"K2 is so far from the Sun and so cold, we know for sure that the activity--all the fuzzy stuff making it look like a comet--is not produced, as in other comets, by the evaporation of water ice," explained research team leader David Jewitt of the University of California at Los Angeles.

"Instead, we think the activity is due to the sublimation [a solid changing directly to a gas] of super-volatiles as K2 makes its maiden entry into the solar system's planetary zone. That's why it's so special. This comet is so far away and so incredibly cold that water ice there is frozen like a rock."

Volatiles are chemical elements and compounds that have low boiling points and are found in the crusts or atmospheres of celestial objects such as planets, moons, and comets.

K2's coma is being formed through the Sun heating its volatile gases, including nitrogen, oxygen, carbon dioxide, and carbon monoxide, all of which coat its surface as ice. The comet has not yet developed a tail.

By the time most comets are discovered, usually near Jupiter's orbit, they have already lost their surface volatiles.

Scientists plan to observe K2 over the next few years as it heads toward its closest approach to the Sun, just beyond Mars' orbit, in 2022.

Its discovery is reported in a paper published in The Astrophysical Journal Letters.

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