A comet visited by a NASA spacecraft this month is spewing jets of vaporized dry ice into space, scientists have found.

"Previously it was thought that water vapor from water ice was the propulsive force behind jets of material coming off of the body, or nucleus, of the comet," said Jessica Sunshine, a professor of astronomy at the University of Maryland who is deputy principal investigator for the mission in which the Deep Impact probe visited Comet Hartley 2.