Comet Holmes and the case of the Disappearing Tail

But what's a Comet, anyway?

An ontological debate ensued, mostly in private, but recently resulting in the public ejection of Pluto from the category of "planet". In this debate, the retention of a solar system cosmogony - including attachment to a primeval outer comet reservoir with links to the present (the Oort Cloud) - has been a significant feature.

Why do comets split?

Yet as far back as 1989, Carl Sagan and Nancy Druyan had remarked on the fact that 80 per cent of comets which split do so when they are far from the Sun.

In their book Comet, they wrote:

The gravitational tides of the Sun or unequal heating cannot be sole causes of the splitting of comets. We still do not know why comets split.

Stranger still, Dr Brian Marsden, for many years astronomy's Mr Orbital Elements extraordinaire, had noted in the 1960s that two comets, 1882 II and 1965 VIII, looked as if they had split apart near aphelion (their farthest distance from the Sun), beyond the orbit of Neptune and above the ecliptic plane. Has nothing progressed?

Contemporary authorities such as David C. Jewitt of the Institute for Astronomy, University of Hawaii, concede that still "most splitting events occur without obvious provocation and their cause is unknown". (See pdf, 1.2MB.)

This has not stopped cometologists devising ever more complex structures for comets to account for the more evident facts: some comets are conceived of as comprising an icy core well sealed in a rocky shell; others as having a refractory mantle for their orbital phase. But can the counter-intuitive nature of such theoretical elaborations equal some of the more counter-intuitive facts which recent observations have adduced, such as the production of X-rays?

Some commentators think that the standard narrative of comets has been allowed to grow in an ad hoc manner for too long.

The Institute of Electrical and Electronics Engineers (IEEE) has for many years had a Nuclear and Plasma Sciences Society subgroup, and has published papers since 1986 on the application of plasmas to the phenomena of astronomy. A 7th series is underway.

Countering the astronomical consensus, plasma physicists account for comet features in terms of a varying electrical potential experienced by the comet as it changes location within the electrical plasma field. This is the "solar wind" - centred on the Sun - which extends beyond Pluto, and which is modified by the magnetic and electrical contribution of the planets.

In this account, cometary comae and tails are the result of electrical arcing, analogous to electrical discharge machining, rather than sublimation.

The dual flashes of light observed when the Deep Impact spacecraft mission despatched a copper impactor into Comet Temple 1 were consistent with the expectations of plasma physicists. Scientists observed two flashes: the second flash was due to the impact, but the first flash was due to electrical discharge between the comet and the impactor, and resulted in failure of the on-board data collection and transmission systems.

A compilation of predictions about the Deep Impact encounter from the point of view of a plasma universe can be found here.

So a possible fragmentation of comet Holmes is not the only thing to look forward to. Some are asking if God if not after all a crude materialist, but a subtle electrician?

Follow the link above Larry's page for a comet-locating starmap. UK readers should crane their necks round midnight to the zenith, and adjust the gaze slightly north-east. With binoculars the fuzzy coma is clearly visible. ®

*Bootnote

Unlike the rest of science, the "order" of stellar magnitude is not computed to base 10, but to Pogson's Ratio of 2.512. To know exactly why, you would need to build a time machine, travel back to the ancient Greek period, and ask them how they could conceive of a sixth rate star, when you or I might make do with third or fourth rate ones.