Earlier in the year there were predictions that comet ISON would be spectacular - the comet of the century. Projections are more tempered, but its orbit is very unusual and it appears to have originated in the Oort cloud - a distant sort-of part of the solar system about a thousand times farther out than Neptune.
A brief summary from Science News.
Looking ahead, astronomers found that ISON will pass within a cosmic whisker of the sun, close enough to potentially be ripped apart by the star’s intense gravity. As the first known object from the Oort cloud to approach so close to the sun, the comet promises researchers a spectacle of dust, gas and ice brilliantly illuminated by the sun’s light.
And because ISON has probably spent nearly its whole existence in cold storage, astronomers believe it has preserved a record of the conditions that prevailed when the sun and Earth were born. “It gives us a chance to understand what the composition was and what the environment was when the solar system formed 4 1/2 billion years ago,” Knight says.
Reports on ISON’s makeup have already started to come out. In April, a team led by Jian-Yang Li of the Planetary Science Institute in Tucson, Ariz., directed one of the Hubble Space Telescope’s cameras toward ISON and snapped sharp photos of the comet. The researchers found that ISON is average-sized as comets go, with a nucleus roughly four kilometers across.
Based on images taken in different wavelengths of light, Li and his team also discovered a large amount of water ice in the region around the nucleus. That probably indicates large amounts of ice near the comet’s surface, where the sun can easily drive it off, he says. The finding confirmed that ISON is on its first pass through the inner solar system, not a periodic visitor like Halley’s comet.
The Hubble observations also suggested that ISON presents only one face to the sun. Li thinks that ISON’s dark side could bear scars from bombardment by extremely high-energy particles called cosmic rays, which scientists believe whiz around in deep space. Relatively few of these particles make it to the inner solar system because they are deflected by a steady stream of particles known as solar wind and by the sun’s powerful magnetic field; both of these shields stop short of the Oort cloud. ISON could thus provide a rare glimpse of the perilous environment beyond the sun’s protective reach.