Posted on 04/04/2006 2:49:22 PM PDT by blam
Impactor ejects mighty water mass
By Jonathan Amos
BBC News science reporter, in Leicester
Comets hold materials unchanged since the Solar System's formation
The Nasa projectile that slammed into Comet Tempel 1 last year kicked out at least 250,000 tonnes of water.
The figure comes from UK/US scientists on the Swift telescope, one of many observatories called on to study the US space agency's Deep Impact event.
Swift's X-ray data shows more water was released and over a longer time scale than had previously been thought.
Researchers hope the new information will help them understand better the nature and construction of comets.
"In terms of the science, we got a lot of data that really does support the model of how X-rays are produced at comets, and Swift, because of its agility and the quality of its detectors, will be ideally placed to observe another comet when one becomes visible," said Dr Dick Willingale, of the University of Leicester, who led the Swift study.
Long view
The orbiting Swift's "day job" is to hunt down the colossal bursts of gamma-ray radiation that flash randomly across the cosmos.
However, on 4 July last year, it was among a fleet of space and ground-based telescopes asked to watch what happened when Nasa's Deep Impact probe released a 370kg projectile into the path of the 14km-wide Comet Tempel 1.
Swift's main task is to investigate flashes of gamma-ray radiation
The crash released a plume of material that was examined at a range of different wavelengths.
But whilst the other observatories made relatively quick studies and then turned away, Swift continued to look at the impacted "ice mountain" on and off for more than 60 days. Its patience paid off.
Swift's X-ray Telescope (XRT) saw the comet continue to release water for some 13 days after the initial event, with a peak five days on from the collision.
X-rays provide a direct measurement of the colossal amount of water thrown out as a result of the impact - the Earth-equivalent volume of about 100 Olympic sized swimming pools.
Exciting time
The radiation traces the interaction between the neutral water molecules and the solar wind, the stream of charged, heavy particles that continually billow away from the Sun.
"The solar wind particles smash into the cometary particles and a process which we call 'charge exchange' occurs," explained Dr Paul O'Brien, also of Leicester University.
Animated guide: Deep Impact "The upshot is that the heavy ions from the Sun get into an excited state and then they de-excite themselves by emitting photons of light which turn out to be X-rays, typically.
"Essentially, the more material liberated, the more X-rays are produced."
The X-ray power output depends on both the water production rate from the comet and the local conditions of the solar wind in the vicinity of the comet, which at the time was about 130 million km from Earth.
Using data from another satellite called ACE, which constantly monitors the solar wind, the Swift team managed to calculate the solar wind flux at the comet during the X-ray outburst. This enabled them to disentangle the two components responsible for the X-ray emission.
Lifted grains
The question is why the comet continued to eject material for so long after the initial impact.
Comets are continually losing material, especially when they get close to the Sun; and astronomers occasionally see sudden outbursts which are most likely associated with the natural impacts of meteorites.
The explosive moment of impact on Comet Tempel 1
In pictures
But the long period of raised X-ray emission seen in the case of Deep Impact is a bit of a puzzle, especially since other views of the comet at optical wavelengths suggested outgassing died down relatively shortly after the initial hit.
"I have a hunch that the comet got shook up, so that quite a lot of material was lifted but was still loosely bound to the surface. And you can imagine that if you lift ice grains, it is much easier to sublime (turn straight from solid to gas) them; they get exposed to more radiation from the Sun.
"All this is supposition; all we know is that when we put in the numbers we seem to get an excess coming off of about two and a half times over the quiescent level."
The results of the Swift observations of the Deep Impact event are being discussed here at Leicester University, which is hosting this year's National Astronomy Meeting.
This could go a whole lot of different directions! :)
Is there any evidence that this is so?
ML/NJ
I'm surprised.
But, if true, then we know where we can get water in space.
I guess that cured global warming.
In other words, no.
ML/NJ
Deep Impact: 2 satellites proudly built by Ball Aerospace in Boulder Colorado
Like what? (Try not to wave your hands this time.)
ML/NJ
Really? We observe other solar systems forming?
How many "theoretical models" are there? Do you believe in one of them, or all of them?
Theoretical models are just that. They are not evidence.
ML/NJ
Maybe you've noticed I haven't made an argument yet?
ML/NJ
BTW, it's obvious that huge canyons can form, or have been formed, because we see them. How this happened is a little less obvious. Anyone who believes the fairy tale about how the Grand Canyon was formed by the ground rising up around this little river just isn't observing. (Hint: Look at the side canyons.)
ML/NJ
I recall from high school chemistry or physics that the boiling point of water gets lower with decreasing pressure. I don't understand how water could remain liquid, or ice could remain solid, in the vacuum of outer space.
Wouldnt the water all boil off, similar to being "freeze dried"?
Can anyone explain the phenomenon?
Thanks
They have predictive value or are discarded.
For example the theoretical models made predictions for this experiment.
If the data don't match the models are updated to reflect the new evidence.
Just like the interpretation of the Bible. In past days it was interpreted literally to state the earth was the center of the universe. That has been proven false. Smart Christians updated their interpretation, dumb ones updated their interpretation some time later.
In past days it was also interpreted literally to state God created the earth in six days. That HAS BEEN PROVEN false (Absent mental gymnastics like god did it in six days but left millions of years of fossil record as a test of faith. Note that's not the same as proving alternate explantions true). Smart Christians have sense updated their interpretation. Dumb ones are still struggling with this one.
Several icy comets that orbit within the Asteroid Belt like ordinary asteroids hace also been identified. Water is definitely out there whether anybody goes for it or not.
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