The Pinwheel

(Last update 2-23-97)

NOTE: This image was taken by the Hubble Space Telescope on September 26, 1995. The figures below are based entirely upon this image. On about October 23rd the comet experienced a change that definitely effect these figures. Please refer to The Origins Page for documentation of the evolution of the comet Hale Bopp and updated figures as to estimated size.

Fig 2a

Please note that this HST photo was taken of Hale Bopp when it was over 6 A.U. out. The Sun has limited gravitational or radiant heat effect upon the comet at this distance to cause gassing out or seismic activity. JPL states that the lower bright spot is the nucleus and that the upper bright spot is a "chunk" of material being sloughed away. Unless this comet is very unstable, there is no reason for the material to break away. There are only a couple of plausible explanations; First, if it is unstable, this would mean that a magnificent internal seismic event took place. Perhaps volcanic in nature. If that is the case, then there could be imaged several "chunks" at any later date, moving away from the comet. None have surfaced. Second; If this were a separating "chunk" of cometary material, it would not spiral around the nucleus in an apparent even fashion. It would move directly away from the nucleus, even if the nucleus is rotating as it appears. The image below graphically shows that it in fact does not move away.  

Fig 2b

This graphic image of the above reflects two different and important aspects of Hale Bopp. First the size of the comet. Since it doesn't appear likely that out-gassing could take place at this distance, this image is probably as close to the actual size of the comet that we may ever see (more on this later on the occultation page). This comet, as most comets, is not spherical. It is oblong and not a perfect shape at all. The distance of "C" is the broadest measurement at twelve thousand miles! Diameter times Pi = Circumference. If you don't have a calculator handy, that equals roughly 40,000 miles!

This graphic also shows that the trail from the upper bright area is not moving away from what JPL calls the nucleus. A to B = A to X.

A more plausible explanation would be that the upper bright spot and the lower bright spot is volcanic activity occurring on two different areas of the same body.

Update On Cometary Size Verses Nuclear Size:

I have received several arguments stating that they believe in the traditional theory of cometary makeup, or as it is known The Dirty Snowball Theory. This theory states that comets are primarily made of water ice which has silicate (sand) embedded in it. This belief has been modified over the years to include various other occurring elements, such as Carbon Monoxide(CO), Carbon Dioxide(CO2), and other various elements.

The following comments are from a discussion that I recently had with Oliver Hainaut, a PhD "Fellow" from the U of Hawaii.

"At what temperature does CO and CO2 sublimate?"
"I don't remember the temperatures, but assuming a "normal" comet (say, like Halley), H2O will start to sublimate at about 3AU, CO2 at 8, CO at 50AU (yes: fifty). These distances are directly related to the equilibrium temperature of a piece of dark ice put at that distance of the Sun."
"At what temperature does silicate crystallize? Surely at a temp greater than 162K?"
"Yes. but this is not relevant: the silicate dust grains formed before the formation of the solar system and they are floating around since then. They have been mixed with ice and accreted into comets, then the ice sublimate and let them free, but they just float around and reflect light, nothing fancy like evaporation/crystallization for them: it is too cold."
Sublimation is a term that refers to the effect of great extremes in heat and pressure on elements that causes them to go directly from solids to gases. Note that he uses the term "normal comet" and that he gives an absolute distance that these elements start to sublimate within this widely accepted model (H2O=3AU's, CO2=8AU's, CO=50AU's).

In this quote below a significant fact is revealed from Hal Weaver from the HST project. From this quote we can see that the Hubble Space Telescope has a spectroscopic data available:

"The spectroscopic data taken in October show no obvious molecular, atomic, or ionic emissions. In particular, we don't see OH (water), CS, CO2, CO Cameron band emission, C or S."
So in October, after the above images were taken, they are saying that there was NO evidence of the important elements CO, CO2, or H2O, to create a gaseous cloud. There are however other reports that say that there was CO present. As above Dr. Hainaut reports CO can sublimate at a distance of 50AU's. But this report states very clearly that NO CO is found. If the coma was made up of a CO cloud of 12,000 miles in diameter, doesn't it seem plausible that it could be readily documented by the Hubble instrument? Another important point can be found in the following quotes. This point is that "dust" is different than a "gaseous" cloud. Now the theory is that grains of sand are embedded in chunks of ice and are set free by the process of sublimation. But again if this were the case- the dust grains in the ice- the H2O or even the CO could be documented-without a 12000mile doubt! This following quote states the composition of the "sand".
"Observations of the dust in the coma of Hale Bopp have been made with various telescopes. Of special interest are here the infrared, spectral observations of the silicate band in the 10 micron spectral region(IAU Circulars 6444 of 8/5 and 6448 of 8/12). These measurements allow to determine the dust temperature which was found to be relatively high on July 22 (Infrared Telescope Facility, Hawaii) and also to estimate the composition of the dust. For instance, observations with the Canada-France-Hawaii 3.6m telescope on July 8 indicated the presence of crystalline olivine."
This mineral is commonly found on the earth as the product of volcanic activity. This comment gives credence to the theory that Hale Bopp possesses high temperatures. Now high temps at 6-8 AU's doesn't have to mean a surface temperature of 1600 degrees. the temp that it takes to create the crystallized olivine. Olivine and silicates for that matter are of a very high density and mass per molecular weight. And one other comment on the production of dust in this comet. This from the IRAM project on October 22, 1995.
"Although important, this CO production may not be sufficient to explain the huge dust production of this comet observed in the visible. We also searched for other volatiles:HCN,H2CO,CH,OH, which have sublimation temperatures between those of CO and H2O. The search was NEGATIVE, with upper limits corresponding to a few percent the production rate of CO."
MY conclusion based upon these statements is seen quite readily. The coma that is seen in the August and September Hubble pics is nearly nonexistent, due to the fact that it was made up of primarily dust-olivine, a heavy, dense material produced from a volcanic reaction. If the size of Hale Bopp is NOT 12000 miles in diameter, then it isn't much smaller.

Now I know that the argument may be that there have been other findings since that show a greater likelihood of the coma being made of these elements. But these quotes stand as they were given. Unless they would like to go back and redo the measurements at the time they documented them.

I stand on my initial estimations of size, with the only modification that there may have been a minimum dust coma of less than 1-2000 miles of contributing diameter.

Update of 2-10-97

This quote below can be found on NASA's Asteroid and Comet Impact Hazard Page from A. Harris after attending "Tunguska '96", at Bologna, Italy, July 15-17, 1996:
"In the second session, devoted to theoretical modeling of the event, the cometary nature of the Tunguska body was challenged. The essential points are that an icy body of the size needed to produce the energy of the Tunguska event would explode 25 km or more above the ground, whereas a stony body would explode right in the range observed and inferred from the tree fall pattern. (See, for example, Hills and Goda 1993 or Chyba, Thomas and Zahnle, 1993. Both papers argue strongly for a stony composition, a conclusion which has been generally accepted in the West but has not penetrated very deeply into Russia, where the impactor continues to be referred to as a comet). There are of course model uncertainties, so not all participants agreed that these results were definitive. One should keep in mind that we really don't actually know what a comet is. There has been an evolution in the paradigm from "dirty iceball" to "icy mudball" structure, and the truth may be that comets are mostly silicate material, and perhaps even quite hard, with just enough ices to power the coma and tail. The recent entry models also indicate that either an icy or a stony body, upon exploding would completely disintegrate into small particles, most of which would shoot back out of the atmosphere in a plume, like those observed in the comet (or was it?) Shoemaker-Levy impacts on Jupiter. Thus very little residue would be expected on the ground in the impact zone, and the observed "white nights" would be expected, regardless of whether the bolide was cometary or asteroidal. Although the issue of asteroid vs. comet was not resolved, I perceived a slow shifting of attitude among the participants toward a rocky body, whether one calls it a comet or an asteroid."
This appears to support the idea that there is great doubt in the scientific community concerning the makeup of comets, which lends credence to the above hypothesis!

Update 2-23-97

This report below is from the University of Maryland, a clearing house of findings concerning the comet. This particular report reflects support for my above suppositions.

Silicate Emission
P.-O. Lagage and collaborators have reported the first detection of silicate emission from observations on July 8.5. Photometric imaging shows a northeast extension of the coma as far as 35" from the nucleus. The colors integrated over a 24"x24" box imply a continuum temperature of 185K and a peak in an 11-11.45 micron bandpass implying emission by crystalline olivine.
Ray Russell and collaborators have reported detection of a strong silicate emission feature, 70% above the continuum, in an 8-13.5 micron spectrum obtained on July 22.3. Unlike the results above, this spectrum showed a trapezoidal profile for the emission with a flat peak from 9.9 to 11.5 microns, suggesting amorphous silicates.
Further details are on IAU Circular 6448, issued on August 12.
Although this report was issued on August 12,1996, It was just recently released. Why?

  If they knew, would they tell us? 
copyright 1996 gary d. goodwin