Hartley 2 'snowballs'
Hartley 2 'snowballs' Several frames from Deep Impact's Medium Resolution Imager near closest approach to comet Hartley 2 on November 4, 2010 show numerous ice-rich particles that were ejected by the comet, several of which can be tracked from frame to frame. The particles themselves are moving relatively slowly (at less than a meter per second); most of the apparent motion results from the many-kilometer-per-second relative speed of the spacecraft. The particles appear to move in different directions and with different speeds because they are at different distances from the spacecraft. NASA / JPL-Caltech / UMD / Brown University

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