posted 02-22-2002 04:01 PM            

No Prob.

You'll notice that the photographs were taken with a digital camera (Pictor CCD) with a Meade Schmidt-Cassegrain telescope. This is a very common setup (I have an 8-inch SC, as does, I believe, 3T3L1).

More important to the view, though, is the fact that most of the exposures were a minute or more. This was necessary for the CCD (charge-coupled device -- the equivalent of 'film' in a digital camera) to pick up the very faint tail of the comet.

Understand that the tail is the subliming gas from the comet body itself, which is usually described as a 'dirty snowball', i.e., made up of frozen gases with some dust thrown in. Since the comet is usually first viewed as it approaches the sun, there is little gas in the tail. As the comet moves closer to the sun, the sun's heat causes the gas to sublime and the solar wind pushes the tail away from the comet. That is why, no matter where the comet is, its tail always points away from the sun.

Anyway, in order to get the faint tail to show up, the camera's shutter is open for a minute or more. The comet, which would be bright enough to be picked up with a two- or three-second exposure, is overexposed. Unlike film, where the overexposure ends up getting lighter and lighter, the light actually migrates from one CCD to another based on VERY slight movement of the scope. As a result, the coma (or 'head' of the comet) gets fuzzier and expands to four or five times its actual size.

The end result is that you're seeing the tail at 'actual' size, but the coma, due to over-exposure, appears to be much larger than 'actual' size. That's why you see the tail come out of what looks like the 'center' of the coma.

Dear Krissa:

I regret to have to disagree.

There has been only one close-up examination of a coma that I am aware of: The Borrely flyby by DS-1 in September 2001. There was, to the best of my knowledge, no reading of any radiation except reflected light and IR.

The last time that anyone earth had an opportunity to inspect the coma was about 60 million years ago when the Chicxulub comet landed in what is now the Gulf of Mexico, wiping out the dinosaurs -- and quite a bit of the remaining terrestrial life on Earth.

And there is no evidence with which I am familiar that supports a hypothesis that comets are collecting material rather than losing it. Of course, as the comet sweeps in from the Kuiper belt or Oort cloud, it will collect, even with its extremely weak gravitational field, motes of dust and ice; but I believe that much more is sublimed away by the sun's heat, ejected from the coma, and escapes the comet's gravitational field forever.

Regards,

Duncan Kunz
Mesa Arizona

posted 02-22-2002 08:12 PM            

Scanner, I've seen the pic's and don't think that there's really unusual there and I think Krissa likes little green things so you're pretty safe.

Krissa, there are a lot of theories about comets going around. I'll agree with Duncan that most are frozen ice balls, but a few could have more to them. As for the radiation part, I did remember that when Comet Hyakutake passed by the earth some time ago, X-Ray emissions had been detected. I also found that comet Hale-Bop also seemed to emit radiation. Now if these are truly ice balls, then why do they emit X-Ray and infrared radiation?

First X-Rays from a Comet Discovered

A team of U.S. and German astrophysicists have made the first ever detection of X-rays coming from a comet. Their discovery of a strong radiation signal -- about 100 times brighter than even the most optimistic predictions -- was made March 27, 1996, during observations of Comet Hyakutake using Germany's orbiting ROSAT satellite. "It was a thrilling moment when the X-rays from the comet appeared on our screen at the ROSAT ground station," said Dr. Konrad Dennerl of the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany. Following the initial detection, the team reported repeated X-ray emissions from the comet over the next 24 hours. The comet was near its closest approach to the Earth at a distance of less than 10 million miles when it was first detected by ROSAT. The strength of the X-ray emission from Comet Hyakutake took the astronomers by surprise, and they are also puzzled by the rapid changes in their intensity. "We had no clear expectation that comets shine in X-rays," said Dr. Michael J. Mumma of NASA's Goddard Space Flight Center (GSFC) in Greenbelt, MD, but the opportunity to search for this radiation in a comet coming so close to the earth was too good to miss. Now we have our work cut out for us in explaining these data, but that's the kind of problem you love to have."
http://heasarc.gsfc.nasa.gov/docs/rosat/hyakutake.html

Hyakutake emitted 100 times as many X-rays as predicted. This was surprising because comets don't possess the kind of nuclear furnace needed to produce such energetic radiation. Scientists speculated that the nucleus might reflect X-rays in sunlight, but the rays did not seem to originate at the nucleus.Instead, the X-rays originated about 20,000 kilometers ahead of the nucleus, in a region called the coma. (The coma is the gauzy cloud of gas and dust spewed from the comet's nucleus that accounts for the comet's cotton-ball appearance.) According to experts at NASA's Goddard Space Flight Center in Greenbelt, MD., the X-rays probably were made in a shock wave produced by the collision between the coma and the solar wind .
http://whyfiles.org/011comets/hya_lessons.html

April 10, 1997
INFRARED RADIATION
FROM COMET HALE-BOPP

by CHANDRA WICKRAMASINGHE1 and FRED HOYLE2
1 School of Mathematics, University of Wales Cardiff, P.O. Box 926, Senghennydd Road, Cardiff CF2 4YH, U.K. Wickramasinghe@cardiff.ac.uk
2 102 Admirals Walk, West Cliff, Bournemouth BH2 5HF, U.K.

Summary

The infrared spectrum of Comet Hale-Bopp over the wavelength range 7.5 to 45 micrometers, obtained when it was at a heliocentric distance of 2.9 AU, is shown to be consistent with a model dominated by a mixed microbial culture including diatoms with an approximately 10% mass contribution from crystalline olivine. Crystalline olivine by itself is unable to account for the data. Observations of infrared radiation emitted by small particles in the coma of Comet Hale-Bopp have recently been published (Crovisier et al. 1997). Intensity values in units of Janskys (10-26 W m-2 Hz-1 steradian-1) were given at wavelengths from about 7.5 to about 45 micrometers for observations made on 6 October, 1996 when the comet had a heliocentric distance of 2.9 AU.
http://www.panspermia.org/infrared.htm

posted 02-22-2002 11:48 PM            

I'm not surprised that the comet emmited IR. When light hits almost anything, a portion of it is turned into heat, which, of course, is IR. But that x-ray emission is still something. Dan, you are the man.

Two side notes. Fist, for those of you who don't know, the term "AU" is astronomical unit, which is the average distance from the Earth to the Sun, or about 93 million miles.

So when the comet was at a "heliocentric distance of 2.9 AU", it was 269 million miles away, out past the orbit of Mars.

Second, I haven't a clue as to what Hoyle and Wickramasinghe (who are very well known in their field, by the way) are talking about when the say things about diatoms. Are they saying the comet comprised diatoms which are the calcium carbonate skeletons of tiny animals? I need to research that more myself.

But thanks for the post, Dan. Now there're two sets of research you've got me doing!

Regards,

Duncan Kunz
Mesa, Arizona

posted 02-23-2002 06:36 PM            

Duncan,I am not putting down my gun for nobody especially when I'm aiming for one of them jets.

Scanner, here's some information about Hoyle and Wickramasinghe if you're curious.

Sir Fred Hoyle, a world-renowned astronomer, is acknowledged to be one of the most creative scientists of the 20th century. He has held the position of Plumian Professor of Astronomy at Cambridge University, and was also the founder of the Institute of Astronomy at Cambridge. He is currently an Honorary Fellow of both Emmanuel College and St.John's College Cambridge and an Honorary Professor at Cardiff University of Wales. He is best known for his seminal contributions to the theory of the structure of stars and on the origin of the chemical elements in stars. He is a joint proponent of the Steady-State model of the Universe, and in collaboration with Chandra Wickramasinghe he has pioneered the modern theory of panspermia.
http://www.cf.ac.uk/maths/wickramasinghe/hoyle.html

posted 02-23-2002 06:59 PM            

ROSAT Detects X-ray Emissions from Jupiter during Comet Shoemaker-Levy 9 Impact
Dr. J. Hunter Waite, Jr., Dr. G. Randall Gladstone, and other investigators analyzing data from the German Roentgensatellit (ROSAT) report the detection of bright x-ray emissions from Jupiter's northern hemisphere during the impact of one of the Comet Shoemaker-Levy 9 fragments on July 19.

Observations made with the ROSAT High Resolution Imager (HRI) during the impact of comet fragment K show intense x-ray emissions not present before or after the impact and clearly correlated with it. The emissions appear to originate from a region in Jupiter's high-latitude northern hemisphere that is connected by magnetic field lines to the impact site in the southern hemisphere. Electrons, energized by the impact and accelerated along the field lines to a conjugate region in the northern hemisphere, are the most likely source for the observed x-rays. The collision of these highly energetic electrons with the gases in Jupiter's upper atmosphere produces x-rays through a mechanism known as bremsstrahlung. The emissions observed at the time of the K fragment impact appear to be extremely well correlated with ultraviolet emissions seen by the Hubble Space Telescope. Besides the high-latitude x-ray emissions, emissions from near the magnetic equator have also been identified in the HRI data. These low-latitude emissions may be caused by precipitating energetic neutral atoms resulting from increased charge exchange reactions involving energetic ions in Jupiter's radiation belts. http://www.jpl.nasa.gov/sl9/rosat2.html

posted 02-23-2002 11:34 PM            

Understand that the scientists are saying that the X-rays are originating from Jupiter and from the fact that the comet struck Jupiter. In other words, the X-rays are probably caused by a major disruption (i.e., the comet fragment) of Jupiter's magnetic field.

Remember, Jupiter is not just "an Earth-type planet on steroids".

First, it's a gas giant with a rotation of about 10 hours. That means that its surface (if you call what Jupiter has as a 'surface') at the equator is travelling at around sixty or so thousand miles per hour. Without the abrupt change from atmosphere to either liquid oceans or solid land that the Earth has, just the static buildup in the atmospheric components would cause tremendous potentials which could easily, under stress, release massive amounts of radiation in all spectra (including X-rays). And what better stress than a comet fragment coming in at 20 thousand m/sec?

Second, Jupiter is so big that it almost ignited its own fusion reaction during the formation of the solar system 4.5 Gyears ago. In other words, Jupiter is a "failed sun". But it is big enough, astronomers think, that there is an ongoing thermonuclear reaction (or at least a nuclear reaction) in the core which causes Jupiter to actually give off more heat than it receives from the sun. With something that big and that unstable, seeing massive amounts of X-ray emissions is quite likely.

Finally, although Fred Hoyle and Chandra Wickramasinghe are very good -- and popular -- astronomers, two of their hypotheses, steady-state and panspermia, are extremely controversial. If you've ever read Hawking's "Brief History of Time", he makes a pretty convincing argument for an ever-expanding universe. And Hawking is not only the greatest physicist alive, but maybe the greatest physicist ever. That boy ain't no slouch.

Panspermia? It has a lot of adherents. It's not considered bogus, like Immanuel Velikovsky or anything. But there are a lot of other high-horsepower physicists and cosmologists that disagree with them on that.

Now I don't know enough to even weigh in. One astronomy course certainly doesn't make me even a well-read layman -- when you start throwing concepts like that around!

All I'm saying is that there're several sides to the story....

Duncan Kunz
Mesa, Az.

posted 02-25-2002 01:14 PM            

I am in no way an astrophysicist, (I'm not sure if I even spelled the word right) but I have known Dan long enough for some of his knowledge to rub off on me.

One thing that somewhat puzzles me is that if there is water in these comets, where did the water come from in the first place. And if there once was a planet where the asteroid belt is today, then should there not be some trace of core material or something at least with some amount of detectable radioactivity in it? Now hypothetically, could the comets that we see today be the remnants of the core material of such a planet or possibly more than one? Or could there have been failed planets such as Jupiter with a weaker gravitational field that for some reason developed an unusual orbital pattern? The sun, after all is a variable star and may have spit out far more material than previously thought and at different times during the course of the development of the solar system?

NEW AURORAL ACTIVITY
The HST detected unusual auroral activity in Jupiter's northern hemisphere just after the impact of the comet's "K" fragment. This impact completely distrupted the radiation belts which have been stable over the last 20 years of radio observations.
Aurorae, glowing gases that create the northern and southern lights, are common on Jupiter because energetic charged particles needed to excite the gases are always trapped in Jupiter's magnetosphere. However, this new feature seen by Hubble was unusual because it was temprorarily as bright or brighter than the normal aurora, short-lived, and outside the area where Jovian aurorae are normally found. Astronomers believe that the K impact created an electromagnetic disturbance that traveled along magnetic field lines into the radiation belts. This scattered charged particles, which normally exist in the radiation belts, into Jupiter's upper atmosphere.

X-ray images taken with the ROSAT satellite further bolster the link to the K impact. They reveal unexpectedly bright X-ray emission, mainly from the north foot of magnetic field lines connected to the impact site, that was brightest near the time of the K impact, and then faded.

posted 02-25-2002 02:22 PM            

"I am in no way an astrophysicist, ..." No one else here is either. I'm sure not LOL!

"...the FOS detected emissions from silicon, magnesium, and iron that could only have originated from the impacting bodies, since Jupiter itself normally does not have detectable amounts of these elements."

True. Jupiter, like most gas giants, has a methane-'n'-ammonia (reducing) atmosphere, probably like we had 3 Gyears ago. The gas giants never evolved to an oxidizing atmosphere, even though we (and probably Mars and Venus) did. If there were spectral emissions of Si, Mg, and Fe, they probably came from the comet fragments.

"Most surprising were the strong signatures from sulfur-bearing compounds like diatomic sulfur (S2), carbon disulfide (CS2), and hydrogen sulfide (H2S). Ammonia (NH3) absorption was also detected."

Lots of people see the term 'diatomic' and think it refers to 'diatoms' which are the skeletal remnants of single-celled animals. This leads some folks to believe that the emissions provide some validation to the Panspermia hypothesis. Actually, 'diatomic' should be thought of as 'di-atomic', or two atoms in a molecule of sulfur (S2). This does not invalidate Hoyle and Wickramasinghe, of course; they're good guys. The NH3 absorption could come from the Jovian atmosphere; there's a bazillion tons of it there.

"If the comet was merely a dirty snowball as is theorized, would there have been enough of these elements present to have been detected?"

Possibly. In a 'snowball' as big as one of the fragments, you could easily have a metric kiloton worth of 'dirt'. Although that doesn't seem like much, when vaporized it would provide a pretty fair spectroscopic signature. Remember, the typical meteorite we see flash across the night sky is at an altitude of about 100,000 meters (60 miles) and is only as big as a pea - and we can sure see it when it vaporizes!

"One thing that somewhat puzzles me is that if there is water in these comets, where did the water come from in the first place?"

There's a lot of water found throughout the solar system and even out of it. Most of the stuff in outer space is hydrogen gas, of course; but there's enough O2 floating around as the result of old supernovas of Class I type stars that it could combine with the H2. Admittedly, most of the water we know about is in places like comets and planets (maybe even Mars!), but if you use the accretion disk theory of solar system formation, it would model lots of water - much of it tied up in comets.

"And if there once was a planet where the asteroid belt is today, then should there not be some trace of core material or something at least with some amount of detectable radioactivity in it?"

You can get into some really big fights with cosmologists about that one - and you'd have a bunch of 'em on your side, as well. For years, astronomers thought that the asteroid belt was the remnant of a failed planet between Mars and Jupiter (because if you look at the mathematical spacing of planets, another planet should 'fit' in there). But from what I understand, the recent push is that the asteroids, like the comets, were all comet-like accretions of dust and ice as the accretion disk was forming. When the central part of the disk reached critical size and gravitational acceleration and set itself of with a fusion explosion (which is still going on today, of course - that's why the sun still shines), the heat and solar wind blew away all the dust and water vapor from the 'cometoids' where the asteroid belt is today, leaving just rocks and pebbles which accreted into the big asteroids today. The other 'cometoids', being wa-a-a-a-y out in the Oort cloud, were to far away for the solar wind and heat from the new sun to do much as far as blowing their light-weight stuff away.

Anyway, that's one hypothesis. The bottom line is, no one knows for sure. Hopefully, the data from the Jupiter impact will give the chrome-domes stuff to argue about for the next fifty years.

Regards,