Comet ISON: Many JETS Create HAVOC - WHY Comet ISON is Not Breaking Up ?
Why Comet ISON Is Not Breaking Up
Soon after comet ISON was discovered, I started work on the Secular Light Curve (SLC) of this object and found to my surprise that the light curve did not resemble those of other well behaved Oort Cloud comets. The SLC exhibited a Slope Discontinuity Event+U-shape signature after which the comet halted its brightness increase. The comet remained at the same brightness for more than 4 months. This was not normal.
After searching my database of SLCs compiled in the Atlas of Secular Light Curves, it was clear that ISON belonged to a group of comets that had disintegrated after exhibiting the SDE+U-shape signature. It was then in agreement with scientific practice to conclude that there was going to be an impending demise of this comet.
The photometric behavior of the object continued to be abnormal. When the comet reached to about -2.9 AU from perihelion, water sublimation started and the comet began to pick up in brightness again. This was expected and even predicted. What was not expected is that while the brightness increased the water production rate decreased. Once again this was not normal.
On November 14.03 the comet experienced an outburst that increased its brightness by several magnitudes. The water production rate halted its decrease and began to increase. At the same time the comet began to exhibit "wings". High resolution images of the nucleus presented symmetrical wings on each side, like in certain water fountains. Then a Press Release from the Max Planck Institute for Solar System Research pointed out that this could be an indication of disintegration, since comet C/1999 S4 LINEAR had presented wings just before splitting. "Features like this typically occur after individual fragments break off the nucleus", Dr. Hermann Böehnhardt from the MPS, Katlenburg-Lindau, Germany, explained.
An investigation by Gary Kronk resulted in a list of six comets that had exhibited wings and that had disintegrated. So, once again and independently, evidence was uncovered to conclude that this comet was doomed and was going to split.
At the same time, the comet continued its journey toward the inner solar system, crossing 11 Red Lines, and remaining in one piece, a remarkable feat. Each Red Line was the distance at which 11 previous comets had disintegrated.
Thus comet ISON has broken the record of the smallest distance to the Sun, without showing any signs of splitting or disintegrating, for this type of object.
About November 20th, a new outburst of water has been detected and the visual brightness has increased once again. It is now evident that the comet is experiencing recurrent periods of outbursts. The reason of the outburst might be pockets of pristine material probably composed of CO or CO2, implying that the nucleus is inhomogeneous.
It is thus scientifically relevant to ask: why comet ISON is not breaking up?
To answer this question we have to understand first why comets break up. And in that regard I have to mention the case of comet 85P/Boethin that was expected to return to perihelion on 2008 and in spite of a search with 8 meter telescopes, was never found. Using the Secular Light Curve method and using the faintest magnitude limit I was able to calculate the size of the smallest fragment that would be detected with the telescopes: 14 meters. So the comet disintegrated into fragments smaller than this size. You can read about this puzzling story in a paper by Meech et al. (2013) here:
How can a comet disappear from view and leave no trace?
The answer is "jets".
Many images have been published in Internet applying new processing techniques, that bring out the inner region of the coma, and invariably show from 1 to 7 jets of matter spouting out of the nucleus. Due to Newton's third law, these jets exert powerfull forces on the nucleus. They not only change the orbit of the comet, but also change the orientation of the rotational pole. In other words, they create havoc on the normal parameters of the comet. And there is theoretical and observational evidence to conclude that these jets predominantly speed up the rotation of the nucleus. There are a few cases in which the rotation slows down and the rotational period increases, but eventually all comets experience a shorter rotational period that gets shorter and shorter with time. There is even a theoretical limit before the comet splits. With a rotational period of about 3 hours, the comet is at the limit of survivability.
This is a premonitory indication that the comet is going to die by rotational disruption. The nucleus breaks apart due to centrifugal forces that unable it to hold together. And this may happen at any time in any part of the orbit, explaining the disappearence of comet 85P/Boethin far from the Sun and beyond reach of ground based telescopes.
So, rotational disruption due to jets is the culprit of a comet's demise. There are many cases of rotational disruption and just to mention one, 73P/Schwassmann-Wachmann 3 comes to mind. This comet disintegrated into more than a 150 fragments ! You can read about this fascinating story in a paper by Ishiguro et al. (2009) here:
So, let us go back to our question. Why is comet ISON not disintegrating?
There are two reasons. (1) The comet is a slow rotator, thus the powerfull centrifugal forces are not at play. This conclusion is supported by the slow rotational period of 15.7 hours that I found for the comet. And (2) the comet is large, much larger than other comets that disintegrated. So gravity is holding it together. NASA researchers estimated that the nucleus is less than 4 km in diameter. From our own model calculations, the comet is even larger. I would not be surprised if in the final analysis the comet is 4-6 km in diameter. This conclusion is supported by the fact that non-gravitational forces have not been detected on this comet.
Thus comet ISON continues surprising us. And the final surprise would be if it gets in one piece to perihelion and survives in one piece after perihelion. If it does, we will be in the presence of a comet that has broken all records, all predictions and all paradigms, and that will become if not "the comet of the century" (we are only 13 years into the century), at least the "The Great Comet of the Beginning of the Century".
Ignacio Ferrín, 131125
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