Impactor Ejects Mighty Water Mass

BBC ^ | 4-4-2006 | Jonathan Amos

[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.

[Hayzo]

This could go a whole lot of different directions! :)

[ml/nj]

Comets hold materials unchanged since the Solar System's formation

Is there any evidence that this is so?

ML/NJ

[inquest]

So... does this mean the comet has more water than they thought it did? I'm trying to figure out the significance of this in terms of how it affects our understanding of the nature of comets.

[inquest]

I think it's just a conclusion based on models of how the solar system formed. There would inevitably some material left over that wouldn't coalesce into anything resembling a planet. This material would spend most of its time in the cold outer reaches of the solar system, so there wouldn't be much that would cause anything to change.

[Southack]

I'm surprised.

But, if true, then we know where we can get water in space.

[exit82]

I guess that cured global warming.

[ml/nj]

I think it's just a conclusion based on models of how the solar system formed.

In other words, no.

ML/NJ

[inquest]

To the question you asked, I think the answer would be yes, there is evidence to that effect. Cold hard proof, on the other hand, is another matter. So it's just a question of probability based on the evidence. In this case, appparently most astrophysicists rate the probability as quite high.

[JOAT]

Deep Impact: 2 satellites proudly built by Ball Aerospace in Boulder Colorado

[ml/nj]

there is evidence to that effect

Like what? (Try not to wave your hands this time.)

ML/NJ

[inquest]

Like the fact that theoretical models of the early solar system make predictions that are borne out by observations of other solar systems forming.

[ml/nj]

Like the fact that theoretical models of the early solar system make predictions that are borne out by observations of other solar systems forming.

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

[Rebel_Ace]

Previously in this thread:

"...there is evidence to that effect..."

"Like what? (Try not to wave your hands this time.)"

We are talking about processes that take far, far longer than the lifespan of any living thing here on this planet, and range over distances that are literally astronomical. If you are the sort that trots out the "Where's the evidence?" argument because no living person can say, "I personally observed that, and I can replicate it here in a petri dish.", then you are not being reasonable with respect to the subject of astronomy.

So, what evidence? Telescopic observations of solar system sized accretion discs. Telescopic observations of what appear to be proto planets disrupting other such "dust discs". Following along the same lines as a geologist would, after observing water eroding rock and soil, that huge canyons can form, even if the geologist would never live long enough to PERSONALLY watch it happen.

Harping about "What evidence?" to astronomers, as if they could satisfy you only by bottling a star and handing it to you does not make your arguments sound reasonable.

[ml/nj]

your arguments

Maybe you've noticed I haven't made an argument yet?

ML/NJ

[ml/nj]

Following along the same lines as a geologist would, after observing water eroding rock and soil, that huge canyons can form

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

[John Galt's cousin]

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.

Wouldn’t the water all boil off, similar to being "freeze dried"?

Can anyone explain the phenomenon?

Thanks

[Rebel_Ace]

"Maybe you've noticed I haven't made an argument yet?"

Earlier you explicitly asked:

"Really? We observe other solar systems forming?"

This interrogative questions the other poster's position, and implies the following:

(1) You are either un-aware of the current state of astronomical observations, - or -

(2) You don't accept the principle that you can make observations of multiple objects and phenomena at different stages in order to deduce the progress of a SINGLE object or phenomenon where the timescales are far greater than human lifespans allow.

It's just not a good argument.

"...it's obvious that huge canyons can form, or have been formed, because we see them..."

You can say the same thing about Stars and Planets. We see them as well.

"...the Grand Canyon was formed by the ground rising up around this little river..."

My geological example had to do with EROSION, which is the process by which soil and rock are REMOVED by water. I honestly don't know where you are getting the "ground rising up" reference.

Again, not a good argument.

[Dinsdale]

Theoretical models are attempts at explaining evidence.

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.

[RightWhale]

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.