Posted on 09/06/2005 11:45:24 PM PDT by 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.
If comets are so loose why would we need to divert one from a collision course with Earth?
This one has potential.
The Leonid meteor swarm is supposed to be the rocky debris left by a comet. One gets the impression "comet" might be a catch-all term for "objects composed mostly or entirely of gaseous material in highly elliptical orbits."
EPA regulations, probably. Clean Air Act, etc....can't have all those airborne particulates...it's against the law. (smirk)
I donno. We've had threads before about organic material in space. Lemme mull this one over.
What is the volatile material? Dust does not act like a gas... I suggest electricity.
Comets... The intergalactic dust bunny.
And coming soon, the intergalactic version of the dreaded BROOM!!!
:-)
Basic physics.
Force = Mass x Acceleration.
Fluffiness doesn't enter the equation at all.
Either way, BLAMM!
If they are that loosely packed, then a few nukes fired into them should creat a shock wave with all the melting water and methane going up all at once and blowing them apart.
I can't believe all comets are made this way.
Just what are "meteroids", pray tell?
It's a small mass, but mass, nonetheless
Yes, but the mass is fixed, and was known beforehand wasn't it? I would think the mass can be determined from observations of the orbital path. The size of the comet is known, so there was an expectation of the object's density. 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.
I know a meteoroid is but what is a "meteroid". :}
A small meter?
What is the volatile material? Dust does not act like a gas... I suggest electricity.
Color me highly skeptical.
I'm guessing this means the size of a soccer field.
That's Jessica on the right. I think....
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