Deep Impact space collision reveals comets to be fluffy balls of powder

The Guardian ^ | 9/7/2005 | Ian Sample, science correspondent

[Swordmaker]

To medieval observers, they were mysterious harbingers of doom, but thanks to an unprecedented act of celestial vandalism, scientists have unveiled some of the innermost secrets of comets.

Out is the long-held view of hardened, dirty snowballs hurtling through space. In is the comet as a fluffy ball of powder, blowing puffs of dust whenever sunlight falls on it.

The insight came yesterday when researchers announced the first detailed results of Deep Impact, an elaborate experiment played out in space on July 4. Under the gaze of cameras on nearby spacecraft and more than 70 ground-based telescopes, the Deep Impact probe fired a metre-long copper bullet on a collision course with a 4-mile-wide block of dust and ice known as Comet 9P/Tempel 1.

The 23,000mph collision produced a huge crater and gave scientists their first ever look inside a speeding comet.

"Prior to our Deep Impact experiment, scientists had a lot of questions and untested ideas about the structure and composition of the nucleus of a comet, but we had almost no real knowledge," said Michael A'Hearn, professor of astronomy at the University of Maryland and lead scientist on the Deep Impact project.

Prof A'Hearn's team is still trying to locate the crater the projectile gouged out of the comet, because the cloud of dust produced on impact obscured cameras aboard the Deep Impact probe as it flew past. But measurements of the particles knocked out of the comet during the collision revealed some intriguing details of its make-up.

Most striking is that the comet is not made up of very much at all. "It's mostly empty," said Prof A'Hearn. The fine particles of dust and ice are held together extremely loosely, with pores thought to run throughout. "We have deduced that around 75% to 80% of the nucleus is empty and that tells me there is probably no solid nucleus. That is a significant advance in our understanding," said Prof A'Hearn.

The finding overturns the view held by some scientists that comets were hard balls of solid dust and ice. "The outer several tens of metres of the cometary material is extremely fragile," said Prof A'Hearn whose study is published online by Science Express today.

Images of the comet before impact showed it released bursts of gas and dust into space when sunlight heated up its surface.

When Deep Impact's copper bullet slammed into the comet, it produced a crater estimated to be the size of a football pitch and some tens of metres deep. The impact knocked thousands of tonnes of material into space.

Among the material were a host of organic molecules. Some scientists believe that comets carried these compounds to other planets, releasing them on impact, and seeding them with the building blocks of life. "I'd argue that's more likely now, because we saw this big enhancement of organic material coming out on impact," said Prof A'Hearn.

The researchers were also keen to see if their speeding projectile would divert the comet from its orbit, a strategy that might be used in defence should a comet or asteroid be detected on a collision course with Earth.

"What we have learned is important to designing a diversion technique. Knowing it's highly porous and highly fragile is important and knowing how much material came out, and how fast, tells you how efficiently you can transfer energy to it," said Prof A'Hearn.

[GSlob]

Now the only question is, "are these puffs burps or farts".
According to Aristotle ("Problemata", book 33, problem 9, IIRC), burps and farts are the same thing, but proceeding through different outlets.

[Drammach]

The article indicates that the Deep Impact results show the density is 20 to 25% of the expected value. That doesn't seem to add up.

Seriously, this is hard to answer ( for me. I'm no scientist )

The "mass" was known, and the "composition" was generally known. ( I mean, we had a pretty good idea it was icy matter, etc.. )
We knew that because of the orbit, and apparent size, etc.. strictly trajectory and speed and gravity..
However:
We weren't sure of the "properties" of that mass..
Was there a solid core with gas pockets?
Was the comet made up of "ice boulders" ?
Was it all a big "snowball" ?

Apparently, it was a big, fluffy "snowball"..

Learn more at the Deep Impact Site

[Drammach]

they're saying that because this comet appears to be a "fluffy ball of powder," then all comets must be fluffy balls of powder.

My premise exactly.. ( #16 )
Evidence:
The "string of pearls" comet that hit Jupiter...
Shoemaker-Levy 9..

It "appeared" to be made up of a group of icy boulders loosely held together by gravity..
When it approached too close to Jupiter, it broke apart, and on it's return orbit crashed into the planet with spectacular results..

I would argue that we have evidence of more than one way to make a comet..

[Bittersweetmd]

Isn't it something how often scientist prove to be way off track?

[SunkenCiv]

Note: this topic is from September 6, 2005.

Comet Research Pioneer Whipple Dies
AP on Yahoo | 8/31/04 | AP
Posted on 08/31/2004 5:19:39 PM PDT by NormsRevenge

Fred L. Whipple, a pioneer in astronomy who proposed the "dirty snowball" theory for the substance of comets, has died. He was 97... proposed the theory in 1950, saying that comets consisted of ice with some rock mixed in, rather than sand held together by gravity, as was widely believed. Whipple's theory was an attempt to explain why some comets seemed to arrive at destinations earlier or later than predicted... believed that as a comet approached the sun, its light vaporized ice in the comet's nucleus. The jets of particles that resulted acted like a rocket engine that either slowed or accelerated the comet... also theorized that the glowing comet tails contained particles that originated from frozen reservoirs in comet nuclei.

Thanks Swordmaker. Just adding, not pinging.

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