View Full Version : Discussion: Following the Dust Trail

2005-Jun-02, 06:29 PM
SUMMARY: On March 13, 1986, the ESA probe, Giotto, had a close encounter - a close encounter with a visitor from the Oort cloud spewing 18 metric tons of gas every second and pouring 30 metric tons of dust from its nucleus. It's name? Comet Halley... And following its trail was one of the world's foremost experts on cometary dust properties - Dr. Jochen Kissel. "Historically comets have always been unusual bodies, as they seemed to appear out of the nothing and also disappear like that. " But the real mystery is the dust.

View full article (http://www.universetoday.com/am/publish/following_dust_trail.html)

What do you think about this story? Post your comments below.

2005-Jun-02, 08:59 PM
Great Story! loved the interview with Dr. Jochen Kissel.
It's interesting to see some results come together from all of the various comet studies to show us things we can expect when Stardust drops its cargo early next year.

2005-Jun-02, 09:16 PM
Thank you!

I was deeply honoured that Dr. Kissel took the time from his very busy schedule to add his comments. The man is a legend...

It was a privelege to be able to research the story and learn how the science progressed over the years - and in what direction it will go in the future.

Your kind comments are appreciated!


2005-Jun-03, 01:04 AM
WOW! :blink: That is an excellent photo... Halley's Comet no less.

2005-Jun-03, 01:32 AM
The time-of-flight mass spectrometers were a real tour de force. They are still cutting edge technology, representing a reduction in volume and in power consumption by a factor of a thousand or so, with no loss of function. The particle paths are folded electrostatically to yield a path length of useful size. Bloody amazing! S

The Near-Sighted Astronomer
2005-Jun-03, 03:23 AM
Outstanding work Tammy. I learned more about comets reading that article than i ever thought possible. Trulty they are time capsules from the very beginnings of the solar system...

2005-Jun-03, 12:19 PM
Originally posted by The Near-Sighted Astronomer@Jun 3 2005, 03:23 AM
Truly they are time capsules from the very beginnings of the solar system...
I agree that comets are like time capsules from the beginning of the solar system.

But the record in comets has been constantly changing.

Comets have been cycling back and forth between the inner and outer parts of the solar system for almost 5 Gy.

Comets are like the blades on a blender, swirling through the inner and outer parts of the solar system that otherwise remained poorly mixed.

Meteorites and planets that froze into solids in different parts of the heterogeneous proto-solar nebula probably provide a better record of the early solar system.

With kind regards,


2005-Jun-03, 01:35 PM
As I read the article, the numbers at the beginning kept coming back. Halley's comet has really great mass, and probably had really enormous mass when it started its swings around the sun over the billions of years.

One thing I had to start picturing from early on, that was not exactly something commonly described, is the involvement of solar winds. I knew that at some critical zone of its orbit the sun's radiant energy caused the generation of a comma, the tail, which waxed and waned as the body approached and retreated. But this makes me wonder if the solar wind ablates comet material, diminishingly, much of the way back to its apogee and increasingly most of the way back to its perigee--not just in 'the zone' that we observe. It makes me concerned that we might have our hopes up for some incredibly old member of our solar system when it might have been a relatively new member of our solar system. In that respect it might be an older-still body captured from interstellar space while a comparatively new member of the sol system. It may give us info on old matter, but not necessarily our system's old matter.

Another thing that I wonder about, with all that dust and gas. Considering the descriptions that have come from Saturn fairly recently, should we be thinking that some of the moons, and possibly the rings, are captured comets? What we have had displayed for us, literally for centuries, was cometary dust spread out in circles about Saturn? Some of those odd-looking bodies are possibly, then, comets comparatively pristinely preserved, spared the eons of solar ablation, suffering the comparatively smaller pressures and forces of Saturn's system?

Think of that one moon that had dark and light hemispheres. The dark was the ablated side of the comet and the light-colored side is the still frozen icy side, that had it not been captured by Saturn eons ago, would be flaring up a tail in the heated half of its orbit around the sun?


2005-Jun-03, 06:04 PM
Something more came to mind when looking at information on the New Horizons series of ventures by NASA from another article in UT. In that thread, through NASA, I looked again at the plan for the Pluto mission. The NASA summary described the cold conditions and that there was a hint of water ice. This reminded me of the water detected in comet tails, as mentioned in this story.

I remember decades ago when a friend of mine was working on his chemistry doctorate. When you ask what he was doing, he would smile and say, "I freeze water." It seems, although I never had the chance to read the whole study, that at very cold temperatures water freezes differently. Water ice on objects in or from our solar system's further reaches, may not fully resemble the snow and ice we on earth are accustomed to. There will be densities, crystaline properties, etc. that will differ from some people's perception.

2005-Jun-04, 12:30 PM
If comet Hale spits out 172,800 tons of gas and dust every hour how long will it be before the comet is no more???

2005-Jun-04, 12:44 PM
Originally posted by Martin@Jun 4 2005, 12:30 PM
If comet Hale spits out 172,800 tons of gas and dust every hour how long will it be before the comet is no more???
Comet Hale-Bopp only spewed that much gas and dust near perihelion. We can figure out how many hours of perihelion passage it could endure:

It is estimated that Hale-Bopp's nucleus is roughly a sphere 40 kilometers in diameter, so it has a volume of 32,000 cubic kilometers, which is 3.2x10^13 cubic meters. If each cubic meter has a mass of about a ton (density of water), then the comet will shrink to nothing in (3.2x10^13 / 1.7x10^5) hours. That would be 2x10^8 hours of perihelion passage. Let's average that out to about 4 months per orbit and call each orbit roughly 2000 years. Four months is about 3x10^3 hours. So roughly Hale-Bopp will disappear after 60,000 orbits, or 120 million years. Keep in mind that the orbit will change, and that Hale-Bopp will spew less stuff as it gets older and smaller, so this calculation only shows the current state of the comet, and the extrapolation is for comparison purposes only.

2005-Jun-04, 06:08 PM
Wow! Look at all the terrific responses!

One of the most fascinating properties of comets that I discovered during the course of researching the article was their very organic nature. This was just not something I readily understood and accepted until I studied all the chemistry aspects. And each and every one of them are different!

In my understanding, comets are "visitors" from outside our solar system and began their birth just as accretion formed. They are truly part of the nebula that spawned Sol. Without giving away future article ideas, they often expire and become what we commonly classify as asteroids... But I can tell you that asteroids are much more than they seem as well!

Do they burn out? Yes. Eventually they will. But do you realize how many more lay in wait? As we know, the stars in our galaxy are always moving... And this shift in gravity is all it takes to send yet another on its journey toward another star - be it Sol in our own solar system or one yet to be discovered.

Our research has already proved that amino acids could exist within a comet. What will StarDust return? What will Rosetta discover beneath the surface? What will happen when Deep Impact creates a natural event when we are close enough to watch?

Enquiring minds want to know... ;)