Comet creates its own 'snowstorm'

Comet Hartley 2 travels with an ice storm of its own making, according to NASA scientists who've been studying stunning new photos of a recent flyby of the comet.
This image from NASA's EPOXI mission spacecraft shows an active end of the nucleus of comet Hartley 2. Icy particles spew from the surface. ((NASA))

Comet Hartley 2 travels with an ice storm of its own making, according to NASA scientists who've been studying stunning new photos of a recent flyby of the comet.

Closeups of the comet — which is peanut-shaped and just 1.2 kilometres long — show a storm of small, light-coloured dots near the comet's nucleus.  

The pictures were taken two weeks ago when NASA's EPOXI spacecraft encountered Hartley 2 at a distance of 700 killometres.

"The EPOXI spacecraft revealed a cometary snowstorm created by carbon dioxide jets spewing out tons of golf-ball to basketball-sized fluffy ice particles from the … comet's rocky ends," said NASA in a release.

The findings astounded scientists.

"Our mouths just dropped," said EPOXI mission co-investigator Pete Schultz at a news conference Thursday. "This looks like a snow globe that you've just shaken."

The new pictures reveal that Hartley 2 is unlike the other four comets that have been examined up close by spacecraft.

One of the first images beamed back of the Hartley 2 comet is shown. ((NASA))

"This is the first time we've ever seen individual chunks of ice in the cloud around a comet or jet definitively powered by carbon dioxide gas," said Michael A'Hearn, principal investigator for the spacecraft at the University of Maryland.

NASA engineers think that nine very small ice particles hit the spacecraft, which was travelling at about 40,000 km/h. But they don't think any damage was done.

The spacecraft "sailed through the Hartley 2's ice flurries in fine working order and continues to take images," said Tim Larson, EPOXI project manager at NASA's Jet Propulsion Laboratory.

The spacecraft has been taking 3,000 images daily for a few weeks and will continue to snap photos until after U.S. Thanksgiving on Nov. 25.

The pictures have also revealed that different parts of Hartley 2 behave differently. The smooth areas in the middle show water evaporating below the surface and turning into water vapour that flows out through the comet's porous surface.

The rough areas on each end, on the other hand, were where the distinctive carbon dioxide jets spewed out their cloud of ice particles.   

Further analysis is needed to figure out how long Hartley 2's snowstorm has been raging.