University of Maryland | 10 Nov 2010
Hartley 2: Primordial Dry IceInitial science results on comet released from University of Maryland, much more to come UMD scientists say.
One of the biggest comet findings coming out of the amazing images and data taken by the University of Maryland-led EPOXI mission as it zipped past comet Hartley 2 last week is that dry ice is the 'jet' fuel for this comet and perhaps many others.
- This enhanced image, one of the closest taken of comet Hartley 2 by NASA's EPOXI mission, shows jets and where they originate from the surface. There are jets outgassing from the sunward side, the night side, and along the terminator -- the line between the two sides. [i](Credit: NASA/JPL-Caltech/UMD)[/i]
Images from the flyby show spectacular jets of gas and particles bursting from many distinct spots on the surface of the comet. This is the first time images of a comet have been sharp enough to allow scientists to link jets of dust and gas with specific surface features. Analysis of the spectral signatures of the materials coming from the jets shows primarily CO2 gas (carbon dioxide) and particles of dust and ice.
"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 University of Maryland Astronomy Professor Jessica Sunshine, who is deputy principal investigator for the EPOXI mission. "We now have unambiguous evidence that solar heating of subsurface frozen carbon dioxide (dry ice), directly to a gas, a process known as sublimation, is powering the many jets of material coming from the comet. This is a finding that only could have been made by traveling to a comet, because ground based telescopes can't detect CO2 and current space telescopes aren't tuned to look for this gas," Sunshine said.
Sunshine and other members of the EPOXI science team are meeting all this week at the University of Maryland to analyze the very large amount of data from the closest approach, and new data continues to come down at a rate of some 2000 images a day.
The Deep Impact spacecraft that flew past comet Hartley 2 has three instruments -- two telescopes with digital color cameras and an infrared spectrometer. The spectrometer measures the absorption, emission and reflection of light (spectroscopic signature) that is unique to each molecular compound. This allows Maryland scientists to determine the composition of the material on the comet's surface, in the jets, and in the coma, or cloud of particles around it. They have found that water and carbon dioxide dominate the infrared spectrum of comet Hartley 2's environment and that organics, including methanol, are present at lower levels.
This is no surprise to scientists. But what is surprising is that there is a lot more carbon dioxide escaping this comet than expected. "The distribution of carbon dioxide and dust around the nucleus is much different than the water distribution, and that tells us that the carbon dioxide rather than water takes dust grains with it into the coma as it leaves the nucleus, said Assistant Research Scientist Lori Feaga. "The dry ice that is producing the CO2 jets on this comet has probably been frozen inside it since the formation of the solar system."
http://www.nasa.gov/epoxi
http://epoxi.umd.edu/
Centauri Dreams | 11 Nov 2010
eep an eye on the EPOXI site at the University of Maryland. New images from the Hartley 2 comet encounter are coming in, some of them truly breathtaking, as is the one at left. The jets clearly visible in the image can be linked with distinct areas on the surface of the comet, the first time we’ve ever seen a comet with this degree of clarity. Image by image, the tiny comet is yielding its secrets. We now learn that spectral analysis of the material coming from the cometary jets shows it to be primarily carbon dioxide, along with dust and ice particles.
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With new data arriving at the rate of 2000 images a day, we should have much more to look forward to from Hartley 2, but the amount of carbon dioxide escaping the comet has proven to be the biggest surprise so far. It’s fascinating to realize that the dry ice producing the jets we see in the images has most likely been inside the comet since the earliest days of the Solar System. The EPOXI findings are consistent with what Deep Impact found at Tempel 1 back in 2005, though mission scientist Tony Farnham (University of Maryland) explains why the Tempel 1 results were less conclusive:
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Taking Deep Impact to a second comet, then, has paid big dividends in the Hartley 2 data, which now point to carbon dioxide rather than water as the driver for cometary surface activity here and likely on other comets. We’re learning about comets step by step — EPOXI’s mission marks only the fifth time we’ve had close-up imagery of one — but we’re finding things no ground-based telescope could show us. The montage below puts all five cometary investigations into perspective.