Gallery: Spacecraft Flies Through Cosmic Snowstorm
01hartley-2-snow-globe
New images from the EPOXI mission show that comet Hartley 2 is a cosmic snow globe. The first science results from the Deep Impact spacecraft's [Nov. 4 flyby](http://stag-komodo.wired.com/wiredscience/2010/11/epoxi-comet-flyby/) of the comet, presented in a press conference today, show the comet's drumstick-shaped nucleus is surrounded by chunks of ice ranging from as small a snowflake to as large as a basketball. "When we saw images come down, even in real-time in the raw data, and realized we had a cloud of snow around the nucleus, we were astounded," said planetary scientist [Michael A'Hearn](http://www.astro.umd.edu/people/ma.html), leader of the EPOXI mission that sent the spacecraft to its icy encounter. "To me this whole thing looks like a snow globe you've shaken," said planetary scientist [Peter Schultz](http://www.planetary.brown.edu/html_pages/schultz.htm) of Brown University. Explore the comet's surprising snowy landscape in the slides that follow. *Image: NASA/JPL-Caltech/UMD*
02hartley-2-flurry
This zoomed-in image from the spacecraft's high-resolution camera shows the snowstorm, which mostly comes from carbon dioxide jets spewing from the comet's knobbly ends, A'Hearn said. "That swarm of points around the nucleus? Those are not stars, they are all chunks of ice," A'Hearn said. The spacecraft flew within 435 miles of the comet at a speed of 27,000 mph, a potentially dangerous way to navigate an ice field. Initial data showed that the spacecraft made it through unscathed, but engineers monitoring the spacecraft's health found that some of these tiny particles smacked the spacecraft hard enough to knock it slightly, though not dangerously, off-kilter. There were 9 possible ice strikes by crystals that weighed between 0.02 and 0.2 milligrams, "about the weight of an eyelash," according to [Tim Larson](http://epoxi.umd.edu/1mission/bios/bio-larson_t.shtml), a mechanical engineer and EPOXI's project manager. Despite their small size, such tiny particles could knock the spacecraft around because the probe was flying so fast. *Image: NASA/JPL-Caltech/UMD*
03epoxi-particles-flying
Follow-up observations showed that the large chunks of ice are "more like a dandelion puff that is easily broken apart, than an ice cube," said [Jessica Sunshine](http://www.astro.umd.edu/people/jess.html), an astronomer at the University of Maryland and EPOXI's deputy principal investigator. "That might be why we didn't see hits on the spacecraft." Deep Impact's extreme speed also let scientists watch the ice particles zip by. In this animation, a star moving through the background is marked in red. The icy particles, marked green, blue and light blue, dance around randomly. "When we first saw this, our mouths just dropped," Schultz said. *Image: NASA/JPL-Caltech/UMD/Brown*
04hartley-2-3d-glasses
The scientists were able to construct a 3D image, called an anaglyph, of Hartley 2's entire nucleus and the cloud of particles surrounding it. __Below:__ In case you don't have 3D glasses, here's a normal, monocular view. [](http://stag-komodo.wired.com/wiredscience/?attachment_id=42752) *Image: NASA/JPL-Caltech/UMD/Brown*
05hartley-2-water-and-ice
One of the biggest surprises from the flyby was that the comet seems to spew carbon dioxide, dust and ice from its bulbous ends, but not so much from the skinny smooth neck. Instead, a plume of water vapor sprays from the comet's midsection. "To our great surprise, there's a tremendous amount of water vapor coming out of the waist," Sunshine said. One explanation is that the comet's midsection is coated in small particles of dust, which is why it looks so smooth. On the bumpy lobes, carbon dioxide is heated by sunlight and boils off, dragging dust and water ice with it. But maybe the dust blocks sunlight from reaching the waist, Sunshine suggested. Water ice turns to water vapor and percolates through the dust. It's also possible that the midsection lost all its carbon dioxide long ago, or that it never had any to begin with. "We don't really know yet," she said. *Image: NASA/JPL-Caltech/UMD*
06hartley-2-and-tempel-1
Scientists saw similar water vapor plumes in 2005, when the same spacecraft smacked a probe into the comet Tempel 1. "This comet is so different from Tempel 1," A'Hearn said. "They work differently because they have different compositions inside. Hartley 2 probably has more carbon dioxide than any of the comets for which carbon dioxide has been measured." Comparing the two comets can help give scientists a window into how the solar system formed. "We really want to understand how things got mixed up in the early solar system when the planets were being made," A'Hearn said. "We want to use this to constrain how the planets formed -- in other words, how we got here." Even though Hartley 2 is now behind it, the spacecraft's work is far from done. Deep Impact is still snapping photos every two minutes, and will have collected 120,000 images by Thanksgiving. "It will give an exhaustive view of this comet, more than we've ever been able to return from any other comet," Larson said. *Image: NASA/JPL-Caltech/UMD*
