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Rubyait Great Old One Joined: 10 Sep 2004 Total posts: 1783 Location: Not telling Gender: Unknown |
 Posted: 05-07-2005 15:02 Post subject: |
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Comet's crater hidden, but plume tells story
| Quote: | Seeing the crater produced by the Deep Impact mission's violent encounter with Comet Tempel 1 on Monday – one of the mission's key goals – could now be impossible.
The plume of gas and dust kicked up by the impact was much bigger, brighter and less transparent than expected. As a result, the crater itself, hidden behind the plume, will be very difficult to detect in the images taken by the flyby spacecraft.
But the science team has already figured out some indirect ways of determining the crater's dimensions, if the optical images cannot provide enough information. In any case, any problem with getting data on the crater challenge is far outweighed by the wealth of information returned from the first-ever deliberate comet impact.
And the show may go on for a while yet. Measurements by the Hubble space telescope and other observatories show the comet continued to brighten - and its new plume of ejected material continued to expand - for at least several hours after the impact.
And if the impact exposed a lot of fresh, volatile material at the bottom of the crater, the growing plume "could go on for weeks", according to the mission's chief scientist, Mike A'Hearn, at mission control at NASA's Jet Propulsion Laboratory in Pasedena, California, US
NASA has produced a series of videos showing:
http://www.nasa.gov/mov/121520main_HRI-Movie.mov
http://www.nasa.gov/mov/121527main_MRI_impact.mov
http://www.nasa.gov/mov/121530main_its_approach_x4.mov
Clearly, the science team has plenty to work on. Analysis of infrared images should soon reveal the precise temperatures of every part of the comet’s surface. This, in turn, will reveal how solid or porous the surface is, by showing how quickly it heats in response to changes in the amount of sunlight it receives.
As for the crater, it should be cooler than the surface, meaning it could be revealed by the infrared images.
And because the ejected plume casts a very clear shadow on the comet’s nucleus in optical images, it should be possible to determine the size of the plume's base - and that should correspond exactly to the size of the crater.
Impact depth
Analysis of the exact shape of the plume as it developed could also show just how deeply the impactor penetrated into the nucleus, and even the consistency of the materials, and whether it has a layered structure.
The plume will be crucial in revealing the composition of material in the comet's hidden interior, via spectroscopic analysis which is still being processed.
There are also the spectacularly detailed images of the comet's mountain-sized nucleus, taken before impact, which reveal a highly varied surface. The science team will try to interpret crater-like rings, dark linear scarp-like features, flat areas, and scattered bright patches.
Until that analysis is completed the science team is sticking to food analogies. A'Hearn said the nucleus "does not look like a pickle or a cucumber, it's closer to a loaf of bread or a muffin". And Jay Melosh, another Deep Impact team member, said that its internal porosity may make it "weaker than the weakest soufflé".
http://www.newscientistspace.com/article.ns?id=dn7629
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| sunspot8 Yeti Joined: 03 Apr 2004 Total posts: 61 Location: England Gender: Male |
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| BlackRiverFalls I wear a fez now.
Joined: 03 Aug 2003 Total posts: 8716 Location: The Attic of Blinky Lights Age: 44 Gender: Female |
| Posted: 05-07-2005 17:23 Post subject: |
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Weird little Point-of-view movie, if I'd seen that in a film I'd have said it looked sooo phoney 
I don't know why but I imagined a comet would look different, sort of, well comet-ish, rather than something I couldn't have told from an asteroid or a small moon.
Still very nice:D |
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| Mighty_Emperor Divine Wind
Joined: 18 Aug 2002 Total posts: 19943 Location: Mongo Age: 42 Gender: Male |
| Posted: 06-07-2005 00:10 Post subject: |
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| Quote: | Astrologer sues Nasa over probe
A Russian astrologer is suing Nasa for crashing a probe into a comet, claiming it has distorted her horoscope.
Marina Bai is seeking $300m (£170m) in damages, saying the probe's impact on Comet Tempel 1 violated her "life and spiritual values".
She had tried to have a Moscow court prevent the experiment from taking place but her action was rejected.
Nasa smashed the washing machine-sized "impactor" into the comet at a distance of 133m km from Earth on Monday.
'Interference'
"It is obvious that elements of the comet's orbit and associated ephemera will change after the explosion, which interferes with my practice of astrology and deforms my horoscope," Ms Bai told the Izvestia daily newspaper.
Nasa scientists hope the experiment will reveal new information on the Solar System's original make-up and perhaps even how life on Earth emerged.
Ms Bai, from Moscow, said the Tempel 1 comet held an important place in her family history, as her grandfather wooed her grandmother by showing her the comet.
Her lawyer, Alexander Molokhov, said the case was based on solid legal ground, since Nasa has an office in Russia, located in the premises of the US embassy in Moscow.
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Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/europe/4649423.stm
Published: 2005/07/04 15:16:45 GMT
© BBC MMV |
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| Rubyait Great Old One Joined: 10 Sep 2004 Total posts: 1783 Location: Not telling Gender: Unknown |
| Posted: 14-07-2005 16:28 Post subject: |
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Comet impact gave 'powder plume'
| Quote: | Scientists studying the impact on Comet Tempel 1 say the material which burst from the collision site was extremely fine, much like talcum powder.
The researchers on the Deep Impact mission say this suggests the icy body probably built up over a long time.
Scientists continue to analyse the data gathered when a 370kg Nasa probe was deliberately slammed into the comet.
The 4 July event was pictured from the passing main spacecraft and a range of space and Earth-bound telescopes.
They caught the vast and dramatic plume of debris that spread out into space.
Images of this material, taken at different wavelengths, should give researchers the best information yet on how comets are put together.
These giant balls of ice, dust and rock are thought to contain the pristine, leftover building blocks of our Solar System, formed when a huge cloud of gas and dust collapsed about 4.6 billion years ago.
The best yet
The Deep Impact science team continues to wade through gigabytes of data collected during the encounter with the comet, which measures 5km wide by 11km long.
"The major surprise was the opacity of the plume the impactor created and the light it gave off," said Deep Impact Principal Investigator Dr Michael A'Hearn, of the University of Maryland, College Park.
"That suggests the dust excavated from the comet's surface was extremely fine, more like talcum powder than beach sand. And the surface is definitely not what most people think of when they think of comets - an ice cube."
The impactor and flyby craft returned approximately 4,500 images.
"We are looking at everything from the last moments of the impactor to the final look-back images taken hours later, and everything in between," added A'Hearn.
"Watching the last moments of the impactor's life is remarkable. We can pick up such fine surface detail that objects that are only four metres in diameter can be made out. That is nearly a factor of 10 better than any previous comet mission."
The Deep Impact team says the impactor hit at an approximately 25 degree oblique angle relative to the comet's surface.
X-ray puzzle
The ensuing debris plume expanded rapidly above the impact site at about 5km/s.
Scientists are still trying to get a good match on the size of the crater. They believe it was at the high end of original predictions, which ranged up to 250m wide.
Researchers using Europe's XMM-Newton space telescope report that Comet Tempel 1 is a very weak source of X-rays.
The team is not sure why - although such emissions have been observed in comets before.
It is possible the X-rays arise from an interaction between the high-speed, ionised particles streaming from the Sun (the solar wind) and the dust particles in the comet's diffuse halo, or coma.
Or, it could just be those coma particles are simply scattering X-rays coming from the Sun.
The University of Maryland in the US is responsible for overall Deep Impact mission science, and project management is managed by the Nasa's Jet Propulsion Laboratory in California.
http://news.bbc.co.uk/1/hi/sci/tech/4672157.stm
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| Rubyait Great Old One Joined: 10 Sep 2004 Total posts: 1783 Location: Not telling Gender: Unknown |
| Posted: 19-07-2005 10:20 Post subject: |
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Deep Impact may never glimpse comet crater
| Quote: | NASA's Deep Impact may fail to live up to its billing as the first mission to look inside a comet. Computer processing designed to correct the spacecraft's defocused camera cannot fully correct the images taken just after impact. If the situation cannot be rectified, there will be no way of seeing the newly formed crater - one of the mission's major goals.
Deep Impact sent a 370-kilogram projectile into comet Tempel 1 on 4 July. Scientists had hoped to use the flyby spacecraft to see the bottom of the resulting crater in order to glimpse the comet's interior composition. They also wanted to see the crater's sides to look for layering, rather like the geological strata on Earth. Several groups had even placed bets on the crater's size, with estimates ranging from 10 to 250 metres. Now, the prize fund could go unclaimed.
The problem lies in the High Resolution Instrument (HRI) on the flyby spacecraft. In March, mission managers discovered it was out of focus. The fuzzy images were blamed on moisture settling in the camera during the spacecraft's final few hours on the launch pad and during its flight through the Earth's atmosphere. Scientists tried to bake-out the moisture. But when that failed to fix the problem, they turned instead to image-processing techniques, which they felt could restore the images.
Dust mask
Unfortunately, the techniques only work on high-contrast images. And when the impactor struck Tempel 1 at more than 10 km per second, it raised more dust than anyone expected. This masked the surface features, rendering them too faint for computer processing to reliably correct.
But scientists are still in contact with the spacecraft and are re-calibrating HRI, says Deep Impact's principal investigator, Michael A'Hearn at the University of Maryland in College Park, US. Despite the probe now being far out of reach of the comet, NASA can use the new calibration data to reprocess the impact images. "We still hope to see the crater," A’Hearn told New Scientist.
Even if the crater images are lost, A'Hearn believes the mission was a great success. "Our view is that we went to a new place and have done exciting new science, just perhaps not as much as we had hoped," he says.
Andrew Coates, an astrophysicist at Mullard Space Science Laboratory at University College London, agrees: "This is not a failure. We scored a direct hit on a comet and have a lot of interesting data."
http://www.newscientistspace.com/article.ns?id=dn7688
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| Rubyait Great Old One Joined: 10 Sep 2004 Total posts: 1783 Location: Not telling Gender: Unknown |
| Posted: 08-09-2005 11:17 Post subject: |
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Comet shakes conventional wisdom
| Quote: | The Deep Impact comet collision is helping astronomers piece together the early ingredients that went into making the Solar System.
Comets are thought to contain material relatively unchanged since the formation of the Solar System 4.6 billion years ago.
Spitzer Space Telescope data confirms the presence of many expected cometary ingredients, but others are a surprise.
Details have been presented at a scientific meeting in Cambridge.
Smashing probe
In July, the Deep Impact spacecraft released a 372kg projectile into the path of Comet Tempel 1. This "impactor" smashed through the surface, kicking out a massive plume of dust, gas and ice.
Spitzer was observing the dramatic collision using its infrared spectrometer. The results show that Comet Tempel 1 contains clays, carbonates and hydrocarbons amongst other ingredients.
Spitzer scientist Carey Lisse, of Johns Hopkins University, US, presented the results at the American Astronomical Society's Division of Planetary Sciences meeting in Cambridge, UK.
Seeds of life
Comets are thought to be cosmic time capsules, containing "pristine" material unchanged since the formation of the Solar System 4.6 billion years ago.
They are also thought to have seeded Earth with the chemical building blocks required for life. By analysing the material ejected from Tempel 1, scientists hope to learn more about how our Solar System formed and how life got started on our own planet.
The presence of carbonates and clays is intriguing, said Dr Lisse, because of the light they shed on the character of the early Solar System.
These substances can only form in the presence of liquid water; so if the material inside Comet Tempel 1 is relatively pristine, then the early Solar System must have been a churning mass, allowing lots of mixing between the planetary building blocks.
"The material is unbelievably fragile," said Dr Mike A'Hearn, principal investigator on the Deep Impact mission. "You could pick up a chunk of it like you were picking up good powdered snow for skiing, except it would mostly be dust. "The various pieces are held together so weakly that you could break them up on any spatial scale, big or small."
Rosetta stumped
Although a fascinating result, it spells bad news for the European Space Agency's Rosetta mission, which seeks to put a lander on comet Churyumov-Gerasimenko in 2010.
Now, Dr A'Hearn says the powdery structures might pose problems for Rosetta's lander Philae, which has to grip on to the surface.
The Philae lander would use its mechanical legs to dig diagonally into the surface of Churyumov- Gerasimenko to hold itself down.
"It means it's really hard to understand how you're going to attach the Rosetta lander to the surface. They have to think about that seriously," Dr A'Hearn told the BBC News website.
"How it's going to work with this incredibly weak stuff, I'm doubtful. I don't think the gravity's strong enough for it to sink in, but if there is any outgassing that will whip it back up."
But Dr Bernard Foing, chief scientist at the European Space Agency, said that comets were a diverse group of objects and that scientists had designed the Rosetta mission to cope with a range of different landing scenarios due to the uncertainty over the nature of comets.
http://news.bbc.co.uk/1/hi/sci/tech/4222788.stm
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| Rubyait Great Old One Joined: 10 Sep 2004 Total posts: 1783 Location: Not telling Gender: Unknown |
| Posted: 09-09-2005 09:31 Post subject: |
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Comet’s minerals hint at liquid water
| Quote: | The comet crashed into by NASA's Deep Impact spacecraft on 4 July 2005 contains material apparently formed by liquid water and not ice, according to new observations with the Spitzer Space Telescope.
This could suggests the disc of gas and dust from which the solar system formed got mixed together billions of years ago, whisking matter from warm regions near the Sun outward – or that an unknown process may allow a layer of liquid water to exist beneath the dusty coatings on comets.
Spitzer was one of the 80 or so telescopes trained on Comet 9P/Tempel 1 when it rammed into the 370-kilogram copper-tipped impactor sent into its path. A spectrometer on the telescope detected a mix of materials as they streamed off the comet, including crystallised silicates, clay and carbonates.
Clay and carbonates are thought to form in liquid water, which can only exist for long periods on the surface of planets or other objects no further from the Sun than Mars. But comets such as Tempel 1 are thought to have formed as smaller chunks of material smashed together around the orbit of Neptune – where any water would be in the form of ice.
"How did clay and carbonates form in frozen comets?" says Carey Lisse, an astronomer at the University of Maryland in College Park, US, who observed the impact with Spitzer. "We don't know, but their presence may imply that the primordial solar system was thoroughly mixed together, allowing material formed near the Sun where water is liquid, and frozen material from out by Uranus and Neptune, to be included in the same body."
Dredged up
This argues against the standard theory that dust and gas in a disc around the Sun simply clumped together with other material at the same distance from the star.
The mixing up of solar system material could happen if the disc behaved like molasses, with clumps of material pulling in their surroundings as they swirled in spiral paths around the newborn Sun, about 4.5 billion years ago. "You can dredge material from near the infant Sun all the way out," says Lisse.
But he acknowledges he is "going out on a limb" with his interpretation and that another process might allow the carbonates to form inside the comet at its present distance.
"I'm thinking more that there may have been a [suitable] environment in the comet itself," says Paul Weissman, a comet researcher at NASA's Jet Propulsion Laboratory in Pasadena, California, US.
Rewrite the books
He says the comet is heated by the Sun, and this heat can travel downward some distance into the comet. "It doesn't seem to get that far down because we see ice excavated from the impact," he told New Scientist.
But if it can travel through the dust that coats comets – which may be up to a metre thick, it may melt some of the water ice. It is not clear whether the carbonate-forming reaction would need a process that prevents the added pressure – created by any melting – from venting water into space.
The discovery of carbonates "creates problems one way or another," he says. But if the mixing theory is true, "it would rewrite how we think about the solar nebula".
The research was presented on Wednesday at a meeting of the American Astronomical Society's Division of Planetary Sciences in Cambridge, UK.
http://www.newscientistspace.com/article.ns?id=dn7971
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| Rubyait Great Old One Joined: 10 Sep 2004 Total posts: 1783 Location: Not telling Gender: Unknown |
| Posted: 03-02-2006 11:30 Post subject: |
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Deep Impact mission reveals comet's icy cargo
| Quote: | Water ice is present on the surface of Comet Tempel 1, suggest observations from NASA's Deep Impact mission. This is the first direct detection of exposed water ice on a comet.
But the mission’s science team says the water ice is present in surprisingly small amounts, covering less than 1% of Comet Tempel 1’s surface. The finding suggests the comet’s surrounding cloud of gas and dust may largely be fed by underlying ices, rather than by gas streaming off its surface.
Old assumptions about comets are faltering as results emerge from data collected by the Deep Impact spacecraft in July 2005, when the probe's impactor detached from the mother ship and crashed into the comet at 37,000 kilometres (23,000 miles) per hour.
Combining high resolution images and infrared spectra collected during the probe's approach, a team of nearly two dozen scientists pinpointed three patches of water ice on the surface of the comet's "upper" half.
The team also found the comet was much weaker structurally than previously believed; the soufflé-like comet is more empty space than rock and ice.
The consensus model of a comet leading up to the Deep Impact experiment is no longer valid, says Don Yeomans at NASA’s Jet Propulsion Laboratory in Pasadena, California, US, a member of the mission science team. "It's certainly not a dirty iceball or an icy dirtball," he told New Scientist. "It's a very, very weak, dusty structure with interior ices."
What lies beneath
Deep Impact struck an ice-free surface area on Tempel 1, says Jessica Sunshine of Science Applications International Corporation in Chantilly, Virginia, US, who led the new study.
But in analysing the ejecta from the comet after impact, she says, "one of the first things we saw was water ice". This indicates that while water ice is not at the comet's surface, it lies just beneath, within its upper metres.
The team says the surface deposits may be responsible for some of the comet's natural emissions. "But what is perhaps even more interesting is that most of the [emission] jets are not due to surface ice, they're due to subsurface ices that somehow permeate that surface," says Yeomans.
Smaller and smaller
That observation may in turn answer another long-standing question about comets: why do some comets seem to be "turned off", or dormant.
If sunlight must penetrate the dust covering a comet's water ice in order to warm it and produce jets, Sunshine says the Deep Impact findings suggest the ices on such dormant comets may not have run out but merely become sealed – by layers of debris, for example.
One thing is clear, Sunshine says. "People used to think of comets as just a thing that simply sat there and got smaller and smaller [as its water ice evaporated]. But it's clearly more complex than that."
http://www.newscientistspace.com/article.ns?id=dn8670
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| Rubyait Great Old One Joined: 10 Sep 2004 Total posts: 1783 Location: Not telling Gender: Unknown |
| Posted: 14-03-2006 11:26 Post subject: |
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Comets 'are born of fire and ice'
| Quote: | Comets are born of fire as well as ice, the first results from the US space agency's (Nasa) Stardust mission show.
In January, Stardust's sample-return capsule landed in Utah, carrying over a million tiny comet grains inside.
Some of these grains contain material that formed at extremely high temperatures, scientists have found.
This is a surprise. Comets formed in the cold, outer-reaches of the early Solar System, and were never exposed to such extreme heating.
The Sun and the planets began forming out of a gaseous cloud called the solar nebula about 4.6 billion years ago.
This "accretion disc" consisted of a hot inner region and a cold outer region where ice was able to survive.
The high-temperature minerals found in the Stardust samples may have formed in the inner part, where temperatures exceeded 1,000C.
But something must then have transported them out to the cold, comet-forming region known as the Kuiper Belt.
"These are the hottest minerals found in the coldest place, in the 'Siberia of the Solar System'," said Donald Brownlee, chief scientist on the Stardust mission.
"When these grains formed, they were incandescent - they were red or white hot."
Abundant samples
Details of the analysis were presented here at the Lunar and Planetary Science Conference in Houston, Texas.
The Stardust spacecraft encountered Comet Wild-2 in January 2004. It swept up particles from the frozen body of ice and dust, flying to within 240km (149 miles) of the comet's core, or nucleus.
It then released its sample-return capsule as it flew back to Earth at the beginning of this year. The US-built capsule touched down in the Utah desert on 15 January. They are the first cometary dust samples ever returned to Earth.
The high-temperature minerals discovered in the Stardust samples are not oddities.
They appear to be abundant, having been found in about one in four of the particles examined so far.
One of these minerals known as forsterite, which melts at 2,000C and condenses at 1,127C, has been detected in a comet before.
But other minerals found in the Stardust samples resemble so-called calcium-aluminium inclusions (CAIs), which form at even higher temperatures.
"This raises as many questions as answers. We can't answer them all just yet," said Stardust co-investigator Dr Mike Zolensky.
Longer distances
There are two main possibilities currently being considered to explain the finding.
If the high-temperature minerals formed at the centre of our solar nebula, the molten droplets could have been blasted out to the cold outer region by powerful gaseous jets called the X-wind.
"It's perhaps indicative that the X-wind model is a good one," Caroline Smith, meteorite curator at the Natural History Museum in London, told the BBC News website.
But it means that these bursts must have carried the minerals much further distances than has previously been suggested.
Alternatively, the minerals may have been formed in the hot regions of other stars before finding their way into the solar nebula, where they were incorporated into comets.
"These are fascinating possibilities," said Dr Brownlee.
"In the lab, we can study these at atomic-level resolution and use the chemical, mineralogical and isotopic properties."
He said that analysis of the different isotopes, or forms, of elements in the mineral should resolve where they originated.
http://news.bbc.co.uk/1/hi/sci/tech/4801968.stm
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| Rubyait Great Old One Joined: 10 Sep 2004 Total posts: 1783 Location: Not telling Gender: Unknown |
| Posted: 17-03-2006 16:14 Post subject: |
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Ice layers record comet creation
| Quote: | The Deep Impact mission is casting new light on how comets formed and how they shed their ice in space.
The US space agency probe sent a 370kg projectile crashing into Comet Tempel 1 and then studied the plume of debris with its suite of instruments.
Nasa's mission scientists say images from last July's encounter reveal as many as seven different layers on the comet's surface.
Their results were presented at a major science conference in Houston, US.
Team member Mike Belton told the meeting he thought the layering was a sign of how comets like Tempel 1 were built up from lesser objects.
Growing 'snowball'
In the outer part of the early Solar System, smaller bodies called cometesimals collided and merged, gradually piling up to form the larger objects we know as comets.
Similar collisions in the inner Solar System led to a loose accumulation of fragments that largely retained their internal structure.
But primordial material in the outer regions was travelling at relatively lower speeds and contained less solid material.
As the cometesimals hit the surface of a growing comet nucleus, they "flowed" on to the surface, researchers believe.
Deep Impact's scientists think the interior structure of Tempel 1 resembles layers of material piled up on one another - a signature of the process that formed the icy body.
Model conflict
Data from the mission is also helping scientists understand how comets shed water-ice through sublimation, the phenomenon which sees a solid become a gas without first melting.
When comets are heated by the Sun, ice sublimes and is lost to space in a process known as outgassing. Some scientists have proposed that this material is coming from deep below the surface crust of the comet.
But temperature data from Tempel 1's nucleus suggests the material must be lost from only a few centimetres below the surface.
"The normal outgassing of the comet has been modelled by different people as coming from bare ice on the surface to subsurface ice that migrates through pores to escape, or from 40-50m below the surface," Deep Impact's chief scientist Mike A'Hearn told the BBC News website.
"I think it is clear from what we have here that the ice that is subliming is within the upper metre. Whether it's 5cm or 20cm below, I wouldn't want to say; but it's not below the top metre. That rules out a lot of the models."
The new results from the mission were presented here at the Lunar and Planetary Science Conference in Houston, Texas.
http://news.bbc.co.uk/1/hi/sci/tech/4816712.stm
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| Rubyait Great Old One Joined: 10 Sep 2004 Total posts: 1783 Location: Not telling Gender: Unknown |
| Posted: 11-04-2006 09:46 Post subject: |
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Hybrid comet-asteroid in mysterious break-up
| Quote: | Something substantial has broken off an icy 50-kilometre object beyond the orbit of Saturn, leaving puzzled astronomers trying to figure out why.
Comets have been seen breaking up before, but only after heating when passing close to the Sun or a gravitational disturbance following a close encounter with a planet.
However, at 1.9 billion kilometres, this object is very far from the Sun. Another mysterious feature is that much more gas and dust is escaping from the breakaway fragment than from the parent body. The disintegration has created a dust cloud more than 100,000 km across and which is several times brighter than the original object was before the event.
The object, called 60558 Echeclus, was discovered in 2000 and is a “centaur” - part rocky asteroid and part icy comet. Its new activity, revealed in images taken on 2 April, makes it look “really strange", says William Romanishen of the University of Oklahoma, US, one of the team that took the images. "The first thing that came to mind was a collision."
Earlier observations showed Echeclus rotates about once every 26 hours, so a fragment would need a push to escape its gravity, says Paul Weissman of the Jet Propulsion Laboratory, who spotted the original cloud of gas and dust around Echeclus on 30 December 2005.
Explosive sublimation
Such an impact on a comet-like body has not been observed before. But there are other possibilities, says Steve Tegler of Northern Arizona University, US, another team member. A likely one is that event was caused by explosive sublimation of volatile ices in Echeclus, resulting in material being blasted off, he says.
Tegler says the evaporating ice is probably carbon monoxide, with vaporises at about that distance from the Sun, where the object's temperature is about 80 degrees Kelvin, close to the sublimation temperature. No one has yet analysed the gas composition.
Another puzzle is the difference in activity between the main nucleus and the fragment. Freshly exposed ices normally sublimate, so "you'd expect equal activity from both pieces", Wiessman says. But the nucleus does not look very active.
Unstable orbits
Echeclus was discovered by the Spacewatch telescope in 2000, and at first looked like an asteroid. Then Weissman found it was surrounded by a coma, so astronomers also classed it as a periodic comet, 174P. The photos from 2 April show the coma has now spread out.
Echeclus belongs to a group of more than 100 centaurs with orbits well outside the main asteroid belt. Although originally from the distant Kuiper belt, they now orbit the Sun between Jupiter and Neptune, but will be ejected from those unstable orbits within tens of millions of years. Cometary clouds have bee reported around three other centaurs too.
Echeclus is currently moving towards the Sun on its 35-year orbit, and will pass closest to our star - about 880 million km - in April 2015. Other centaurs have become active as they moved inward, Tegler says. But none have shown such dramatic activity.
http://www.newscientistspace.com/article/dn8976-hybrid-cometasteroid-in-mysterious-breakup.html
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| Rubyait Great Old One Joined: 10 Sep 2004 Total posts: 1783 Location: Not telling Gender: Unknown |
| Posted: 17-01-2007 12:26 Post subject: |
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Dwarf planet 'becoming a comet'
| Quote: | An unusual dwarf planet discovered in the outer Solar System could be en route to becoming the brightest comet ever known.
2003 EL61 is a large, dense, rugby-ball-shaped hunk of rock with a fast rotation rate.
Professor Mike Brown has calculated that the object could be due a close encounter with the planet Neptune.
If so, Neptune's gravity could catapult it into the inner Solar System as a short-period comet.
"If you came back in two million years, EL61 could well be a comet," said Professor Brown, from the California Institute of Technology (Caltech) in Pasadena.
"When it becomes a comet, it will be the brightest we will ever see."
Cosmic oddball
2003 EL61 is a large object; it is as big as Pluto along its longest dimension. It is one of the largest of a swarm of icy objects that inhabit a region of the outer Solar System known as the Kuiper Belt.
But it is extremely unusual: spinning on its axis every four hours, it has developed an elongated shape.
2003 EL61 is apparently composed of rock with just a thin veneer of water-ice covering its surface. Other Kuiper Belt Objects (KBOs) contain much more water-ice.
Professor Brown's computer simulations show that the object is on a very unstable orbit and set for a close encounter with Neptune.
The eighth planet's gravitational force could either sling the icy rock ball into the inner Solar System as a comet, out into the distant Oort Cloud region, or even into interstellar space.
Orbits of Kuiper Belt Objects tend to be very stable, but the region is thought to be a reservoir for short-period comets.
Occasionally, some of these objects must get tossed inward to become the fizzing lumps of ice and dust that criss-cross our cosmic neighbourhood.
Shedding surface
Mike Brown and his colleagues have come up with a scenario to explain 2003 EL61's physical characteristics and behaviour.
About 4.5 billion years ago, the object that became 2003 EL61 was a ball, half composed of ice and half of rock - like Pluto - and about the same size as Pluto.
Some time early in its history, it was smacked, edge on, by another large KBO. This broke off much of 2003 EL61's icy mantle, which coalesced to form several satellites.
As expected, the satellites seem to be composed of very pure water-ice.
Professor Brown suggested that some of 2003 EL61's mantle may already have made it into the inner Solar System as cometary material.
The oblique impact also caused 2003 EL61 to spin rapidly. This rapid rotation elongated 2003 EL61 into the rugby ball shape we see today.
"It's a bit like the story of Mercury," Professor Brown explained.
"Mercury got hit by a large object early in the Solar System. It left mostly a big iron core, with a little bit of rock on the outside. This is mostly a rock core with a little bit of ice on the outside."
Mike Brown outlined details of his work during a plenary lecture at the recent American Astronomical Society meeting in Seattle.
http://news.bbc.co.uk/1/hi/sci/tech/6268799.stm
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| BlackRiverFalls I wear a fez now.
Joined: 03 Aug 2003 Total posts: 8716 Location: The Attic of Blinky Lights Age: 44 Gender: Female |
| Posted: 17-01-2007 12:43 Post subject: |
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| gosh. only 2 million years to wait for that spectacle! |
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| rynner Location: Still above sea level Gender: Male |
| Posted: 22-01-2007 09:00 Post subject: |
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| BlackRiverFalls wrote: | | gosh. only 2 million years to wait for that spectacle! |
you could go and see this one now:
| Quote: | Giant comet lights up skies
Catherine Boyle in Australia
A comet discovered by a Scottish astronomer has transformed southern hemisphere skies this week.
Thousands of people have gathered in Australia, New Zealand, Chile, Argentina and South Africa to watch Comet McNaught, the brightest comet seen from Earth in more than 40 years. It is one of very few comets that can be seen by the naked eye in daylight and is around 140 million kilometres (87 million miles) from the Earth.
The comet consists of a head bigger than Mount Everest and a tail that stretches 30 million kilometres into space.
The man who spotted the comet, Robert McNaught, 50, originally from Prestwick, Ayrshire, was working at Siding Spring Observatory in New South Wales when he first saw it last August.
It is so bright that some people in Auckland contacted the emergency services fearing that a plane had fallen out of the sky.
http://www.timesonline.co.uk/article/0,,3-2559301,00.html
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tech stuff |
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