NASA spacecraft unravels comet mystery

Feb 15, 2011 by Kerry Sheridan
NASA's Stardust-NExT mission took this image of comet Tempel 1 at 8:39 p.m. PST (11:39 p.m. EST) on Feb 14, 2011. The comet was first visited by NASA's Deep Impact mission in 2005. Image credit: NASA/JPL-Caltech/Cornell

A NASA spacecraft's flyby with a comet showed erosion on the Tempel 1's surface since it skimmed by the Sun in 2005, and revealed Tuesday the first clear pictures of the crater made by a Deep Impact probe.

But the Valentine's night encounter was not easy for the US space agency's Stardust-NExT mission spacecraft, which had to fight an onslaught of debris from the in order to snap dozens of revealing pictures.

"Comets, unlike any other body in the solar system, are unique when they are in the inner part of the solar system where the Earth is," said Don Brownlee, Stardust-NExT co-investigator.

"They are literally coming apart and sending tons and tons of gas and rocks and dust out in space," he said.

"They don't just spew off things in a uniform way. They send off clods of dirt and ice and rock that come apart," Brownlee said, playing audio of the impact sustained by the spacecraft. The sound was like rapid firecracker bursts.

"A good analogy is thinking of a B-17 in World War II flying through flak -- sometimes a large number of impacts in less than a tenth of a second -- so it is a very dramatic environment."

The pictures that Stardust snapped showed some erosion over the past five years, and for the first time allowed scientists to see the crater made by a NASA probe, an impact which was obscured by a huge the first time around.

"We never saw the crater as we went by, it was there somewhere that created a lot of mystery, it also helped to create this mission," said co-investigator Pete Schultz of Brown University.

Tempel 1 was last glimpsed in 2005 by NASA's mission as the comet was shooting toward the Sun on its five-year orbit between Mars and Jupiter.

Deep Impact pummeled the comet with a special impactor spacecraft and the material that came out was a surprise to scientists: a cloud of fine powdery material emerged, not the water, ice and dirt that was expected.

Deep Impact also found evidence of ice on the surface of the comet, not just inside it.

This time, the approach had to be carefully orchestrated so that the spacecraft could snap pictures of the right area of the comet at just the right moment.

"We planned it so on approach we would see the Deep Impact area," said principal investigator Joe Veverka of Cornell University. "That meant arriving at precisely the right time and the right place."

"We saw the crater, we really did see it," said Schultz, making a joke when an image of the crater failed to appear as prompted during a press conference.

"It is subdued. It is about 150 meters across and has a small central mound in the center. It looks as if from the impact the stuff went up and came back down," he said.

"This surface of the comet where we hit is very weak. It is fragile so the crater partly healed itself."

The came closest to the comet at 11:39 pm Eastern time in the United States on Monday, or 0439 GMT Tuesday, at a distance of 181 kilometers (112 miles), NASA said.

The Tempel 1 is about six kilometers (3.7 miles) wide and travels on an orbit that brings it as close to the Sun as Mars and as far away as Jupiter, as they passed.

Comparing pictures of the comet taken in 2005 to the latest ones, Veverka said experts could detect "erosion on a scale of twenty or thirty meters has occurred in the five years since we took this picture."

Other areas seen for the first time appear to show layers of material that have been deposited, a phenomenon that deserves further study, Veverka said.

"They have been interpreted as places where a very volatile gas from below the surface has erupted carrying with it small particles of ice and dust and while some of the stuff leaves into space some of it just flows downhill because a comet does have a little bit of gravity," he said.

"We are seeing changes that we have to spend time quantifying to understand what they mean."

The mission cost NASA about 29 million dollars.

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User comments : 10

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deatopmg
1 / 5 (4) Feb 15, 2011
Sounds to me more like sputtering caused by electrical discharge due to the charge of the solar wind than by vaporization of gasses like CO2 and water followed by explosive depressurizations!

THe vaporization/depressurization paradigm remains even after the first pass of Deep Impact revealed that Tempel 1 was NOT a rocky snowball. The impact of the copper slug suggested that the emissions were due to sputtering.
zealous
5 / 5 (3) Feb 15, 2011
So we got a picture of the comet, they give details about the crater like they got a shot of it. is there any chance they can tell us where the crater is? shoot i could settle for a " lower left hand side (cannot be seen at this distance)"
Quantum_Conundrum
1.1 / 5 (7) Feb 16, 2011
The Tempel 1 is about six kilometers (3.7 miles) wide and travels on an orbit that brings it as close to the Sun as Mars and as far away as Jupiter, as they passed.

Comparing pictures of the comet taken in 2005 to the latest ones, Veverka said experts could detect "erosion on a scale of twenty or thirty meters has occurred in the five years since we took this picture."


This means the comet will totally evaporate in 1200 to 1800 years.

This comet cannot be more than a few thousand years old. Else it would have needed to be the size of a planet in order for anything to be remaining to be seen today. With 20 to 30 meters of erosion in just 6 years, and assuming a similar rate in the past, since it's in a stable orbit, the comet has lost at least 3 to 5 kilometers of it's diameter in just the past thousand years. Since increasing size increases cross section, the comet would have been losing mass at a greater rate in the past, because it would collect more sunlight.
Quantum_Conundrum
1 / 5 (7) Feb 16, 2011
If this comet were even 1 million years old, it would have needed to be over 3300 kilometers in diamter at that time, else it would have evaporated by now.
Bog_Mire
5 / 5 (2) Feb 16, 2011
wow, NASA HR really have made a huge blunder, what with missing out on your obvious authorities on the subject and all...cough, ahem.
JonnyMcA
5 / 5 (6) Feb 16, 2011
@Qunatum Conundrum,

The 20-30 meters erosion was in reference to a lateral erosion of a cliff face across the surface, not 20-30 meters depth of erosion of the entire surface of the comet. The PhysOrg reference is a little out of context. See the official NASA site for further details.
kevinrtrs
1 / 5 (10) Feb 16, 2011
I guess QC is simply re-iterating the problems faced by the current solar model which postulates an age of 4.5 Ga. The question remains - if comets deteriorate so quickly[even if you take into account in this instance we're only talking about a cliff face], how come there are still some left after 4.5Ga?

We know for a fact that nobody has detected or confirmed any viable source for these comets, Oord cloud and Kuiper belt speculation notwithstanding.

Hence the conclusion that if the comets are not that old then the whole solar system can't be older than 100k at most.
RayCherry
5 / 5 (5) Feb 16, 2011
When does a comet become a comet? If the erosion mentioned were of the entire surface, it would still not tell you about the age and/or original size. The question of when the object became a comet would need to be answered to give you an estimate of total erosion caused by close passes to the sun. The only conundrum here is why a smart fellow is making such poor comments recently.
yyz
5 / 5 (4) Feb 16, 2011
@zealous

"So we got a picture of the comet, they give details about the crater like they got a shot of it. is there any chance they can tell us where the crater is? shoot i could settle for a " lower left hand side (cannot be seen at this distance)"

A before-and-after view of the impact site here:

h
ttp://www.nasa.gov/mission_pages/stardust/multimedia/Schultz4.html

A photo gallery of new annotated images of the impact site, among other new (and quite awesome!) imagery, here:

h
ttp://www.nasa.gov/mission_pages/stardust/multimedia/gallery-index.html

that_guy
3 / 5 (4) Feb 19, 2011
3 to 5 kilometers of it's diameter in just the past thousand years. Since increasing size increases cross section, the comet would have been losing mass at a greater rate in the past, because it would collect more sunlight.

QC -
I kinda wanted to give you a good score on this because you actually had facts and calculations. Crackpot theories aside. A larger object will erode more slowly as a portion of its weight due to it's lowered surface area to mass ration, and the increased gravity. So a larger object would have significant erosion mitigation factors.

To address your crackpot remarks.

It's in a stable orbit...at the moment. No one knows how long its orbit has been stable, how large it was to begin with, etc. A stable orbit is one that is less likely to change in the future, without regard for the past that caused it to fall into said orbit.

It could have beeen orbiting past pluto until a 100 years ago, when it got knocked into a new orbit near the sun.

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