A peanut-shaped comet was spewing hundreds of tons of fluffy ice chunks every second as a NASA spacecraft swung by it two weeks ago.
“To me, this whole thing looks like a snow globe that you’ve simply just shaken,” Peter H. Schultz, a Brown University professor working on the mission, said Thursday during a news conference.
The Deep Impact spacecraft passed within 435 miles of Comet Hartley 2 two weeks ago, producing a series of photographs that showed bright jets coming off a rough surface.
What fascinated the mission scientists most was that the chunks of water ice in the jets were not being lifted off the surface by the force of water vapor heated by the sun, but rather by jets of carbon dioxide. This was the first time that such carbon dioxide jets had been observed at a comet.
Frozen carbon dioxide — dry ice — turns to carbon dioxide gas at a temperature of about minus 100 degrees Fahrenheit. Water ice stays frozen until it reaches much higher temperatures. Thus, it appears that the carbon dioxide gas on the comet is blowing apart the still-frozen water ice, along with dust particles, and sending it into space.
The scientists who analyzed the photos of Hartley 2 said that the frozen carbon dioxide within the comet must date from the beginnings of the solar system, because once it turns to gas, it disperses into space. “If it’s there, it’s primordial,” Lori M. Feaga, another member of the science team, said in an interview.
While the bright specks seen in the images ranged in size from golf balls to perhaps basketballs, the spacecraft did not suffer any damage as it flew through the storm at a speed of 27,000 miles an hour.
From the absorption of light by the specks, the scientists deduced that the chunks were not solid ice.
“We’re not seeing hail-size softballs or even ice cubes,” said Jessica M. Sunshine, a deputy principal investigator on the mission. “What we’re seeing are fluffy aggregates of very small pieces of ice. And so, they’re akin more to maybe a dandelion puff that is very empty air that can be easily broken apart.”
The carbon dioxide jets are coming off the two lobe-shaped ends of the comet, which is just three-quarters of a mile long. The spacecraft also found large amounts of water vapor — and not carbon dioxide — emanating from the central narrow waist region between the two lobes. This may mean that, for reasons not yet deciphered, the middle part of the comet does not contain much carbon dioxide, and thus the water ice in it can warm into vapor.
“We wouldn’t expect this at all,” Dr. Sunshine said. “This comet is doing two things at once.”
The Hartley 2 findings differ significantly from what the Deep Impact spacecraft found when it visited Comet Tempel 1 five years ago. At Tempel 1, Deep Impact found water vapor emissions similar to those coming from the middle of Hartley 2, but no carbon dioxide jets and no visible chunks of water ice.
After the Tempel 1 visit, NASA decided to reuse the spacecraft, which still had ample maneuvering fuel left, to head to a second comet. The mission was renamed Epoxi, an amalgamation of two acronyms: Epoch, or Extrasolar Planet Observation and Characterization, which has been using one of the spacecraft’s cameras to look at stars known to have planets, and Dixi, or Deep Impact Extended Investigation, for the second comet fly-by.
“It has emphasized how different comets are from one another and how understanding them is a much more complex problem than the rather simplistic approach I like to normally take,” said Michael F. A’Hearn, Epoxi’s principal investigator.
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http://www.nytimes.com/2010/11/19/science/space/19comet.html?partner=rss&emc=rss
“To me, this whole thing looks like a snow globe that you’ve simply just shaken,” Peter H. Schultz, a Brown University professor working on the mission, said Thursday during a news conference.
The Deep Impact spacecraft passed within 435 miles of Comet Hartley 2 two weeks ago, producing a series of photographs that showed bright jets coming off a rough surface.
What fascinated the mission scientists most was that the chunks of water ice in the jets were not being lifted off the surface by the force of water vapor heated by the sun, but rather by jets of carbon dioxide. This was the first time that such carbon dioxide jets had been observed at a comet.
Frozen carbon dioxide — dry ice — turns to carbon dioxide gas at a temperature of about minus 100 degrees Fahrenheit. Water ice stays frozen until it reaches much higher temperatures. Thus, it appears that the carbon dioxide gas on the comet is blowing apart the still-frozen water ice, along with dust particles, and sending it into space.
The scientists who analyzed the photos of Hartley 2 said that the frozen carbon dioxide within the comet must date from the beginnings of the solar system, because once it turns to gas, it disperses into space. “If it’s there, it’s primordial,” Lori M. Feaga, another member of the science team, said in an interview.
While the bright specks seen in the images ranged in size from golf balls to perhaps basketballs, the spacecraft did not suffer any damage as it flew through the storm at a speed of 27,000 miles an hour.
From the absorption of light by the specks, the scientists deduced that the chunks were not solid ice.
“We’re not seeing hail-size softballs or even ice cubes,” said Jessica M. Sunshine, a deputy principal investigator on the mission. “What we’re seeing are fluffy aggregates of very small pieces of ice. And so, they’re akin more to maybe a dandelion puff that is very empty air that can be easily broken apart.”
The carbon dioxide jets are coming off the two lobe-shaped ends of the comet, which is just three-quarters of a mile long. The spacecraft also found large amounts of water vapor — and not carbon dioxide — emanating from the central narrow waist region between the two lobes. This may mean that, for reasons not yet deciphered, the middle part of the comet does not contain much carbon dioxide, and thus the water ice in it can warm into vapor.
“We wouldn’t expect this at all,” Dr. Sunshine said. “This comet is doing two things at once.”
The Hartley 2 findings differ significantly from what the Deep Impact spacecraft found when it visited Comet Tempel 1 five years ago. At Tempel 1, Deep Impact found water vapor emissions similar to those coming from the middle of Hartley 2, but no carbon dioxide jets and no visible chunks of water ice.
After the Tempel 1 visit, NASA decided to reuse the spacecraft, which still had ample maneuvering fuel left, to head to a second comet. The mission was renamed Epoxi, an amalgamation of two acronyms: Epoch, or Extrasolar Planet Observation and Characterization, which has been using one of the spacecraft’s cameras to look at stars known to have planets, and Dixi, or Deep Impact Extended Investigation, for the second comet fly-by.
“It has emphasized how different comets are from one another and how understanding them is a much more complex problem than the rather simplistic approach I like to normally take,” said Michael F. A’Hearn, Epoxi’s principal investigator.
Read More
http://www.nytimes.com/2010/11/19/science/space/19comet.html?partner=rss&emc=rss
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