Gone But Not Forgotten
- Aug 7, 2001
Cursed said:Cheers, Rynner.
I've been trying to see it for the last few nights, but there are too many clouds between me and it.
Maybe tonight's the night...
(I managed to post without mentioning Ikea. D'oh! Sorry. )
Release No.: 04-01
For Release: 9:20 a.m. EST, Monday, January 5, 2004
Note to Editors: An image to accompany this release is online at: http://cfa-www.harvard.edu/press/pr0401image.html
Suns Of All Ages Possess Comets, Maybe Planets
Atlanta, GA- In early 2003, Comet Kudo-Fujikawa (C/2002 X5) zipped past the Sun at a distance half that of Mercury's orbit. Astronomers Matthew Povich and John Raymond (Harvard-Smithsonian Center for Astrophysics) and colleagues studied Kudo-Fujikawa during its close passage. Today at the 203rd meeting of the American Astronomical Society in Atlanta, they announced that they observed the comet puffing out huge amounts of carbon, one of the key elements for life. The comet also emitted large amounts of water vapor as the Sun's heat baked its outer surface.
When combined with previous observations suggesting the presence of evaporating comets near young stars like Beta Pictoris and old stars like CW Leonis, these data show that stars of all ages vaporize comets that swing too close. Those observations also show that planetary systems like our own, complete with a collection of comets, likely are common throughout space.
"Now we can draw parallels between a comet close to home and cometary activity surrounding the star Beta Pictoris, which just might have newborn planets orbiting it. If comets are not unique to our Sun, then might not the same be true for Earth-like planets?" says Povich.
SOHO Sees Carbon
The team's observations, reported in the December 12, 2003, issue of the journal Science, were made with the Ultraviolet Coronagraph Spectrometer (UVCS) instrument on board NASA's Solar and Heliospheric Observatory (SOHO) spacecraft.
UVCS can only study a small slice of the sky at one time. By holding the spectrograph slit steady and allowing the comet to drift past, the team was able to assemble the slices into a full, two-dimensional picture of the comet.
The UVCS data revealed a dramatic tail of carbon ions streaming away from the comet, generated by evaporating dust. The instrument also captured a spectacular 'disconnection event,' in which a piece of the ion tail broke off and drifted away from the comet. Such events are relatively common, occurring when the comet passes through a region of space where the Sun's magnetic field switches direction.
Cometary Building Blocks
More remarkable than the morphology of the carbon ion tail was its size. A single snapshot of Kudo-Fujikawa on one day showed that its ion tail contained at least 200 million pounds of doubly ionized carbon. The tail likely held more than 1.5 billion pounds of carbon in all forms.
"That's a massive amount of carbon, weighing as much as five supertankers," says Raymond.
Povich adds, "Now, consider that astronomers see evidence for comets like this around newly formed stars like Beta Pictoris. If such stars have comets, then perhaps they have planets, too. And if extrasolar comets are similar to comets in our solar system, then the building blocks for life may be quite common."
Understanding Our Origins
In 2001, researcher Gary Melnick (CfA) and colleagues found evidence for comets in a very different system surrounding the aging red giant star CW Leonis. The Submillimeter Wave Astronomy Satellite (SWAS) detected huge clouds of water vapor released by a Kuiper Belt-like swarm of comets which are evaporating under the giant's relentless heat.
"Taken together, the observations of comets around young stars like Beta Pictoris, middle-aged stars like our Sun, and old stars like CW Leonis strengthen the connection between our solar system and extrasolar planetary systems. By studying our own neighborhood, we hope to learn not only about our origins, but about what we might find out there orbiting other stars," says Raymond.
Other co-authors on the Science paper reporting these findings are Geraint Jones (JPL), Michael Uzzo and Yuan-Kuen Ko (CfA), Paul Feldman (Johns Hopkins), Peter Smith and Brian Marsden (CfA), and Thomas Woods (University of Colorado).
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.
For more information, contact:
David Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7462 Fax: 617-495-7468
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
Wednesday, May 19, 2004. 4:19pm (AEST)
Comets to make joint appearance
Star-gazers will be treated to a rare cosmic event this week when two comets appear in the sky together.
The Cosmos Centre at Charleville, in Queensland's south-west, says it has been inundated with inquiries from locals and tourists.
Spokeswoman Jane Morgan says the 'Neat' comet is making its way through the inner solar system for the first time in recorded history.
She says it is expected to be joined by the 'Linear' comet tonight - which could be another first.
"I have yet to find a time when two comets were in the sky together, so this may be a first," she said.
"If you go on to the astro sites, everyone is just talking about these two great comets and how fabulous it is and aren't we lucky to be here on the planet when it actually happens."
Strange Comet Unlike Anything Known
By Robert Roy Britt
Senior Science Writer
posted: 02:00 pm ET
17 June 2004
A detailed analysis of the comet Wild 2 (pronounced "Vilt 2") has left astronomers astounded at an object that has no known peers in the solar system.
The comet, examined in a close flyby in January by NASA's Stardust spacecraft, has towering protrusions and steep-walled craters that seem to defy gravity. More than a dozen jets of material shoot out from its insides. Dust swirls around the comet in unexpectedly dense pockets.
Among the bizarre features are two depressions with flat floors and nearly vertical walls that resemble giant footprints. They aren't structured like typical impact craters. The features have been named Left Foot and Right Foot in a new map of the comet, which is roughly 3 miles (5 kilometers) wide.
Only two other comets have been seen up close, but both appeared fairly smooth and were nowhere near so heavily cratered. Nor do the pockmarked surfaces common to asteroids and moons bear much stylistic resemblance to the shapes seen on Wild 2.
"So far, as far as we know Wild 2 is a unique object," said Donald Brownlee, an astronomy professor at the University of Washington and Stardust's principal investigator.
Brownlee told SPACE.com that Wild 2 could represent a unique class of comet. He and his colleagues had expected it to be relatively featureless with a dusty, charcoal-like coating. Instead they found a place riddled with apparently ancient impact craters. Broad mesas and steep canyons stand out clearly.
It is more likely, Brownlee added, that Wild 2 will turn out to be a garden variety comet once more of them are studied up close.
Brownlee's group and other research teams present four analyses of Wild 2 in the June 18 issue of the journal Science, building on preliminary results released in March.
Almost no gravity
Scientists don't know exactly what comets are made of. But they're thought to represent the composition of the outer solar system in its primordial state. They're loaded with frozen water and other ices, plus organic materials and silicates, or rock. Many theorists believe comets delivered the water and other pre-biotic ingredients that led to life on Earth.
Stardust flew to within 147 miles (237 kilometers) of Wild 2 on Jan. 2. The observations -- and dust samples that will be returned to Earth in 2006 for lab study -- should improve understanding of the solar system's formation.
Craters on Wild 2, presumably caused by run-ins with smaller objects, are strangely free of the powder, rocks and other debris commonly seen in impact craters on other bodies. Brownlee thinks this is because the comet is a bit like hard, frozen dirt that takes a hit but is brittle, so material flies out.
And because the comet is so small, the material does not fall back.
"There's almost no gravity at the surface," Brownlee said. "If you were standing on [the surface], you could jump into orbit."
Yet Wild 2 is not a fractured pile of rubble that would all fly apart when hit, as some astronomers expected. Brownlee: "We're sure this is a rigid material because it can support cliffs and spires."
Spires shooting up from inside craters "looks like Monument Valley in Arizona," Brownlee said at a press conference today. They likely formed as material around them eroded, indicated that the comet has lost about 328 feet (100 meters) of its surface since birth.
What sort of material can crumble under impact, leave sheer walls and allow its parent body to remain intact?
Previous research in Europe may provide the answer. Scientists made artificial comets of finally powdered organic materials and ice in a vacuum. "They always ended up with a rigid, crusty material," Brownlee said. "If you were standing on it you might go right through it."
He suggested the consistency of the comet is something like freeze-dried astronaut ice cream.
Comets 'blow up'
That all assumes the "footprints" and other depressions on Wild 2 are in fact impact craters. Other forces could be at work.
An image of Wild 2 and a map with features named by the Stardust team.
"Comets do blow up unexpectedly," Brownlee pointed out, adding that built-up internal pressure and "steam explosions" might be responsible for some of the surface features.
In another baffling surprise, Brownlee said, dozens of photos show no small craters on Wild 2, only the large craters that are presumably billions of years old. Perhaps small craters erode away, he said.
Brownlee is also intrigued by the utter lack of similarities between Wild 2 and Phoebe, a fairly small moon of Saturn recently imaged up close by the Cassini spacecraft. Phoebe is thought to be a captured object, having originated -- like Wild 2 -- beyond Neptune. But Phoebe's gently sloping craters, which are riddled with boulders, resemble those seen on asteroids. And Phoebe has many small craters embedded in larger, older craters.
"It's fascinating that they're so different," Brownlee said in a telephone interview.
The two objects may have started out with the same stuff, he speculates, but then underwent different histories. Perhaps like larger objects -- planets and other moons -- Phoebe was once heated enough to melt its insides, which produces a different chemical and mineral structure.
Phoebe is considerably larger than Wild 2 -- about 137 miles (220 kilometers) wide -- so self-gravity could have something to do with the differences. And Phoebe has likely never traveled inside the orbit of Saturn, so it probably has not been hit with solar radiation to the extent now experienced by Wild 2.
Swarms of particles
Comet Wild 2 probably gathered itself together 4.5 billion years ago, just after the Sun was born, in a region beyond Neptune known as the Kuiper Belt.
A 0.13-inch (3.2-mm) projectile created this 4-inch (10-cm) crater with a flat floor and sheer walls in lab material perhaps similar to the composition of comet Wild 2.
In 1974 it had a close encounter with Jupiter and was thrown onto a new orbit that brings it closer to the Sun. A comet loses material when it approaches the Sun, as solar radiation causes ice from its surface to "sublimate" into space, carring dust and larger particles with it. The process creates a cloud of material that reflects sunlight and creates the familiar head of a comet (scientists call it a coma) and sometimes a tail.
Among the new findings: Wild 2 has lost about 3 feet (1 meter) of its surface since 1974.
Stardust flew right through some of that coma material, avoiding boulder-sized objects and grabbing more than 1,000 tiny bits in a specially designed catcher's mitt.
"These things were like a thunderbolt," said Anthony Tuzzolino, a senior scientist at the University of Chicago's Enrico Fermi Institute. "I didn't anticipate running into this kind of show."
Stardust encountered two intense swarms of dust with relative voids in between, suggesting that ejections from Wild 2 come in intense spurts. Comet Halley, studied in a 1986 flyby, exhibited a much smoother distribution of particles.
Large chunks of material are probably ejected from the comet and then fragment into swarms of particles, said Thanasis Economou, another Fermi Institute researcher involved in the study.
More to learn
Comets also lose material when jets of stuff apparently shoot out from inside or, possibly, from surface pockets of especially volatile material. A separate analysis of Stardust data found 20 jets, on both the sunlit side of the comet and, surprisingly, the dark side.
The jets likely emanate from inside the comet, researchers concluded, and they contain water, carbon dioxide and rock particles.
What remains of Wild 2, along with the bits captured by Stardust, is considered pristine. Because this is the comet's first trip to the inner solar system, its composition has been mostly unaltered for the billions of years it spent in the deep freeze. Studying the samples in a lab should provide clues to the state of the solar system at its birth.
But learning whether Wild 2 is common or unique will require visits to other comets, Brownlee said. Two flashy missions are in the works:
The European Rosetta craft, recently launched, will land on a comet in 2014. NASA's Deep Impact will slam a probe into comet Tempel 1 on Independence Day 2005.
Claudia Alexander, a program scientist for Rosetta from NASA's Jet Propulsion Laboratory, has modeled comets for years. She did not expect the number of jets or their ability to lift the large chunks thought to then break up and create the particle swarms. And she's surprised that the comet is apparently not a loosely cemented rubble pile.
"I would have told you it wasn't going to be like that," Alexander said. "We are astonished and intrigued."
Comet put on list of potential Earth impactors
13:17 01 June 2005
NewScientist.com news service
David L Chandler
A comet has been added to the list of potentially threatening near-Earth objects maintained by NASA's Jet Propulsion Laboratory. Comet Catalina 2005 JQ5 is the largest - and therefore most potentially devastating - of the 70 objects now being tracked. However, the chances of a collision are very low.
The listing of Comet Catalina underscores the uncertainty in the knowledge of whether comets or asteroids pose a greater threat to Earth. Previous estimates of the proportion of the impact risk posed by comets have varied widely, from 1% to 50%, with most recent estimates at the lower end.
But comets are larger and faster-moving, on average, so their impacts could be a significant part of the overall risk to human life. And, unlike asteroids, they lie on randomly-oriented and usually highly elongated orbits. This makes them much more likely to remain undiscovered until they are very close to Earth.
Comet Catalina was found by the Catalina Sky Survey, one of the six current, large-scale and automated search programmes for near-Earth asteroids. It was initially designated as an asteroid when first spotted on May 6. But was reclassified as a comet when observers saw characteristic fuzziness in the image, indicating ice and dust streaming off.
Its size is estimated at 980 metres, but Steve Chesley of JPL told New Scientist that the size determination is based on the assumption it is a dark-bodied asteroid, and so the bright coma of a comet would cause the estimate to be high. "It's really an upper limit," he said.
On 26 May, JPL's unique orbital calculation software determined that Comet Catalina was on what could possibly be a collision course with Earth, though the odds of such an impact were small: just 1 chance in 300,000 of a
strike on June 11, 2085. Based on the 980-metre size estimate, that would produce a 6-gigaton impact - equivalent to 6 billion tonnes of TNT.
Astronomers expected the addition of further observations to the calculations to rule out any possibility of a collision, as happens with most newly-seen objects.
But that did not quite happen. The comet's predicted pathway actually drew even closer to making a perfect bull’s-eye with the Earth - its predicted path passes within 1000 kilometres of the where the centre of our 12,700-km-diameter planet will be around that time.
However, uncertainty in the exact timing of the comet’s pass through the line of Earth’s orbit dropped the odds of an impact to about 1 in 120 million. That is very low, but the observations so far cannot categorically rule a collision out.
Chesley adds that even the slim 1 in 120 million odds are an overestimate, because comets, unlike asteroids, can move in unpredictable ways because of the forceful outgassing that creates their dusty comas and tails. "The uncertainty is much larger than we're modelling," he said. “But I haven't come up with a good way of dealing with this."
The only other comet placed on the JPL list of near-Earth objects with possible collision paths was added in 2003. But additional observations ruled out a possible impact - that comet was removed from the list after less than a week.
Just one other comet, Swift-Tuttle, has been recorded with a non-zero possibility of impact. It was rediscovered in 1992 - after more than a century's absence - before the JPL list was created.
Additional observations during Swift-Tuttle’s passage, thanks to the publicity surrounding the possible impact, made it possible to rule out the possibility of an Earth impact anytime in this millennium. However, Swift-Tuttle is on an orbit that will almost certainly cause it to crash into the Earth or the moon eventually.
The US Deep Impact spacecraft is set to slam a washing machine-sized projectile into a comet, to reveal what's inside.
The main spacecraft will release its 372kg "impactor" into the path of Comet Tempel 1 on Sunday, for an expected collision on Monday morning.
By studying the comet's interior, scientists aim to learn more about the formation of our Solar System and the chemical building blocks of life.
Its mission will be short-lived but is certain to be spectacular.
Spacecraft instruments and ground-based telescopes will record the event, as a hole the size of a football stadium is blasted in the comet.
The cosmic fireworks are scheduled for 0552 GMT on 4 July - American Independence Day.
Deep Impact, the spacecraft which carries and ejects the impactor will take pictures and gather data from the collision and its aftermath, 133 million kilometres (83 million miles) from Earth.
Comets are porous balls of ice and rock hailing from the frigid outer boundaries of our Solar System. Periodically, some journey inwards, looping around the Sun.
Like other comets, Tempel 1 contains "pristine" material unchanged since the the Universe formed. This is hidden beneath an outer crust.
"These materials have not seen the light of day for 4.6 billion years," mission scientist Jessica Sunshine told reporters at a news conference in Pasadena, California. But scientists still know very little about the composition of this material.
"Like any good geologist would, we want to hit it (Tempel 1) with a hammer and see what's inside," Dr Sunshine added.
The impactor itself will shatter as the comet crashes into it at 37,000 km/h (23,000 mph), but an onboard camera will record the approach in the last minutes before collision.
Cometary impacts early in Earth history are thought to have first brought water to our planet.
They might also have seeded it with the chemical building blocks required for life. "We want to find out what those materials were," explained Rick Grammier, Deep Impact project manager.
Mr Grammier likened the mission to "a bullet trying to hit another bullet with a third bullet in the right place at the right time". Despite the complexities, team members are confident they won't miss.
Mission manager Dave Spencer said: "We've got good navigation, a good idea of the comet's trajectory and we've been correcting for that all along.
"We're well prepared to position ourselves for this train that's going to run over us."
The impact is expected to excavate a crater more than 25m deep and 100m across, ejecting ice, dust and gas and exposing pristine material.
The Hubble, Chandra, Spitzer and XMM Newton space observatories will be trained on Tempel 1 for the collision, as will ground-based telescopes worldwide.
The mission could inform strategies for deflecting a comet, should one threaten to strike Earth.
"If you are worried about defending Earth from possible impactors, it's a whole lot easier to change the course of something if you know what it is you're changing the course of," said Dr Mike A'Hearn, Deep Impact principal investigator.
This week, astronomers got a preview of the pyrotechnics to come when Tempel 1's nucleus released a short-lived blizzard of particles and gas.
These outbursts seem to occur as comets heat up approaching the Sun.
Probe heads for comet collision
By Paul Rincon
BBC News science reporter
The US Deep Impact spacecraft has launched a projectile into the path of a comet millions of miles from Earth to find out what's inside.
The washing machine-sized 372kg "impactor" should smash into Comet Tempel at 0552 GMT on Monday morning.
By studying the comet's interior, scientists aim to learn more about the formation of our Solar System and the chemical building blocks of life.
Its mission will be short-lived but is certain to be spectacular.
Nasa probe impacts Comet Tempel 1
[pic] The moment of impact viewed in the Nasa control room (nasa)
Nasa scientists say a projectile released by their Deep Impact spacecraft has struck Comet Tempel 1.
The washing machine-sized 372kg (820lbs) "impactor" smashed into the huge icy body right on schedule just after 0550 GMT on Monday.
The 37,000km/h (23,000mph) collision is expected to create a huge crater in the comet and throw off a stream of debris.
The Deep Impact spacecraft, which is watching the event from a safe distance, is sending images to Earth.
Scientists hope the project will give them new insights into the Solar System's composition and the chemical building blocks of life.
The first link gives this:NewScientistSpace.com - NEWSFLASH
Deep Impact smashes all expectations
The comet-crunching probe hurtled into Comet Tempel 1 exactly as
planned, capturing some explosive images in the process.
The impact produced a blast of light so spectacular that it prompted
Mission Control at NASA's Jet Propulsion Laboratory in California to
erupt into cheers and applause.
Click on the link below for the full story on NewScientistSpace.com:
http://www.newscientistspace.com/channe ... tem/dn7622
Science and technology news and features updated daily at
(Pics on page.)Deep Impact smashes all expectations
10:29 04 July 2005
NewScientist.com news service
David L Chandler, Pasadena
Even before the smash, the impactor and the flyby craft returned images the best images ever taken of a comet's nucleus (NASA-JPL) Comet Tempel 1 has smashed into the Deep Impact probe, producing a blast of light that prompted the mission control room at NASA's Jet Propulsion Laboratory in California, US, to erupt into cheers and applause.
Scientists and engineers jumped in the air, pumped their fists and hugged one another. Not only had their mission to deliberately collide with a comet for the first time succeeded perfectly, but the prospect of a damp squib - with the impactor passing right through a diffuse, rubbly comet - had fizzled away.
"Geez, and we thought it was going to be subtle," exulted JPL scientist Don Yeomans, one of the Deep Impact science team. "That was considerably brighter, and had considerably more material coming out, than I had expected," he said.
"We are just ecstatic," said JPL director Charles Elachi of the success of the $330 million mission. "It was worth every penny we spent on it."
Punching a hole
The aim of the cosmic collision was to reveal details about the interior of comets. These bodies of ice and dust a few kilometres across are believed to contain primordial material, preserved in the deep-freeze of space, since the formation of the solar system.
By punching a hole in the comet's crusty surface to release material from below, the mission should reveal details of its composition, through detailed spectral observations. The size and shape of the crater will give information on its structure.
One reason for the spectacular burst released by the comet on impact could be that puncturing the crust released subsurface pressure, allowing a much bigger plume of ejecta to spurt out, Yeomans said. However, it will take detailed analysis over the coming days to confirm exactly what happened 83 million miles from Earth.
Even before the impact itself, the twin spacecraft - the impactor itself, and the flyby craft which moved aside to observe it - were each returning images far more detailed than any previous images of a comet's nucleus. The best previous comet images, taken in 2004 by the Stardust mission, had a maximum resolution of 25 metres. That can reveal objects about one-quarter the size of a football pitch, but the new images are sharp enough to show objects as small as a football.
The pictures show numerous perfectly circular features, which could either be impact craters or sinkholes. They also display long linear features and a varied topography of rough areas and one smooth region - "everything a geologist would love", Yeomans said.
Dozens of observatories on Earth, as well as four in orbit, were also watching the comet at the time of impact, and those images and spectra will be coming in to JPL in the coming days.
"How a washing-machine sized impactor could produce such a large disturbance is going to take some explanation," Yeomans said.
As Nasa controllers whooped and cheered in California at news of Deep Impact's success, their efforts were being watched intently by scientists in far-off London.
Through a live link to a news conference in London, UK space scientists were sharing in some of the delight and fascination of Deep Impact's American team.
This was due in part to the enormous amount of information scientists are certain to glean from the collision.
And British researchers have been observing the collision from telescopes around the world, including the Faulkes Telescope and United Kingdom Infra-Red Telescope (UKIRT) in Hawaii, The INT telescope in Spain and the UK Schmidt telescope in Australia.
But many of the scientists here are also involved in a European mission called Rosetta which aims to orbit and land on a comet for the first time.
Deep Impact, they told reporters, would give valuable insights into what lies in store for the European spacecraft, which was launched in February 2004 on a 10-year trek to Comet 67P/Churyumov-Gerasimenko.
"Deep Impact is beautiful preparation for Rosetta," said Dr Andrew Coates, of the Mullard Space Science Laboratory (MSSL) at University College London.
Rosetta is not designed to crash into its target. Instead, it will catch up with "CG" in 2014 after flybys of Earth, Mars and the asteroids and a three-year period of deep space hibernation.
"Anything we can do to find out more about cometary surfaces is important," Dr Coates told the BBC News website.
The Rosetta flyby spacecraft drops its lander craft towards the surface of CG. The lander then fires a harpoon to anchor it to the comet's surface.
A soft landing is a particular problem given the extremely weak gravitational force exerted by the comet nucleus. The lander, which weighs 100kg on Earth, will on the comet be as light as a sheet of paper.
If there were a slight recoil, it would bounce back like a rubber ball. To prevent this, the lander's three legs are equipped with special shock-absorbers and are fitted with ice pitons which bore into the ground immediately on touchdown.
"One of the big unknowns [of the Rosetta mission] is the internal structure of the nucleus, how it sticks together and the strength of the material," Dr Gerhard Schwehm, Rosetta's project scientist told the BBC News website.
"These are things we hope to learn now from the science of Deep Impact. They help us pin down our scenario when putting the [Rosetta] lander on the nucleus."
Even if they wanted to, the Rosetta team would not be able to make any big changes to the landing stage of the mission. But knowing more about the surface they are landing on will allow mission scientists to check their models of the touchdown, says Dr Schwehm.
Rosetta's Philae lander will determine the composition of surface and subsurface materials using spectroscopy and sample analysis. It will also take high-resolution photographs and carries a radar to determine the internal structure of the comet's nucleus.
One of the big surprises about Monday's impact was the unexpectedly large amount of material excavated by the collision between Tempel 1 and Deep Impact's projectile.
It had been thought that the impact would excavate as much material in 15 minutes as the comet usually discharges in a month.
"I would say it's more like a year," commented Professor John Zarnecki, a space scientist at the Open University in Milton Keynes.
Scientists made some early interpretations. Firstly, the comet's crust is probably weaker than expected.
Professor Zarnecki said it also suggested the material in the comet was probably brittle, a bit like breeze block. Dr Coates likened it to compacted snow.
Dr Schwehm said he thought that a build-up of gases just beneath the surface might have contributed to the large impact.
"When it was triggered by the impactor, they just came out," he said.
But scientists allayed fears that the impact might throw the comet off course, perhaps on a collision course with Earth.
"It was like mosquito hitting a 747. What we've found is that the mosquito didn't splat on the surface; it's actually gone through the windscreen," explained Professor Iwan Williams of Queen Mary, University of London, and a co-investigator on Rosetta.
Though Tempel 1 poses no current threat to Earth, other cometary bodies have wrought devastation on our planet in the geological past. An asteroid or comet impact is blamed for wiping out the dinosaurs at the end of the Cretaceous Period.
"Sixty-five million years ago, one of these things took out the dinosaurs," said Faulkes Telescope director Paul Roche, before the collision. Now, he said, "we're going to get our own back".
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:
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.
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".