The EPOXI mission consists of two parts – the Extrasolar Planet Observations and Characterization (EPOCh) and the Deep Impact Extended Investigation (DIXI). The Hartley 2 observations yielding the snow storm fall under the DIXI portion of the mission. The same craft observed other comets in the past but was unable to observe individual particles of ice ejected from a comet until the Hartley flyby.
The ice chunks from the ends of the comet vary in size from golf balls to basketballs. Their flight from the comet is powered by jets of carbon dioxide gas; images of the comet show that these balls are found around the nucleus of the comet, and that the nucleus is smoother and generates the water vapor seen both in Hartley 2 and in other comets imaged in the past.
Additional observations of Hartley 2 continue. While the spacecraft has been hit by ice balls at least nine times, they were all smaller than the typical snowflake and did not appear to damage the craft in any way. Also, further study is planned in the future to determine how this dual structure came to be. In particular, scientists are interested in figuring out whether the comet formed that way 4.5 billion years ago or somehow evolved into this structure at some point in its travels through space. Either way, the answers should provide more information about the formation and lifecycle of comets.
TFOT previously reported on other recent observations from both space-based and Earthbound telescopes and observatories including the first results from the Allen Telescope Array, the first images from the Herschel Space Observatory, a ribbon of solar material found at the edge of the solar system by IBEX, the detection of black hole eruptions by the Chandra X-Ray Observatory and the observation of changes to a black hole by the Suzaku Telescope.
Read more about the Hartley 2 snow storm in this NASA press release and more about the EPOXI mission on its NASA mission page or its page at the University of Maryland.