Comet Tempel-1 covered in cosmic talc

Dusty

The first data from the Deep Impact mission to Comet Tempel-1 suggest that the comet is covered in a layer of fine powder. When the probe slammed into the comet on 4 July, the impact released an immense cloud of dust, probably as fine as talcum powder, NASA says, leaving a crater between 50 and 250 metres in diameter.

When the impactor hit the comet, it hit at a 25 degree angle to the comet's surface, NASA says. Almost immediately it was vaporised and along with surface and sub-surface material from the comet was ejected back away from the wandering Tempel-1.

The plume of material expanded above the impact site at around 3.1 miles per second. Deep Impact Principal Investigator Dr. Michael A'Hearn of the University of Maryland explains that the opacity and amount of light reflected by the plume are clues to the size of the dust particles.

"[It] suggests the dust excavated from the comet's surface was extremely fine, more like talcum powder than beach sand. And the surface is definitely not what most people think of when they think of comets - an ice cube," he added.

On its way to the surface, the Deep Impact impactor was hit by two coma particles, which knocked the cameras out of alignment for a short period before the craft's attitude control got it back on track.

The research team is currently analysing over 4,500 images taken by the Deep Impact flyby craft and the impactor itself. The images reveal features on the surface of the comet that are only four metres in diameter. This is a factor of ten better than any previous observations of comets, A'Hearn says. ®

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