From: Chandra Wickramasinghe Sent: ‎2015-‎01-‎25 14:13 To: William (Bill) E. Smith Subject: Re: Simple orbit mathematics

Dear Bill

The pressure exerted by sunlight (radiation pressure force) would not be significant for the comet, but only act on the dust escaping from the surface.  That is why the dust tails curve away from the gas tails in comets.  At perihelion the solar energy arriving at the surface would be greater and so raise the surface temperature.  This could have the effect of increasing the sublimation rate of ices, and along with the water vapour gas dust particles could also escape.

However, my view is that the extra solar heat conducted into regions tens of metres deep would lead to warm lakes containing biology, and biological replication with gas production (methane, CO2) would rupture the surface and produce geysers carrying microbes with the gas.

Nuclear energy sources (radioactive decay of Al-26, for example) would be confined to the early history of comets in the solar system.

Does this answer your question?

Best

Chandra: Yes, the tidal forces are totally negligible.

C

Prof. Chandra Wickramasinghe

Dear C, thanks. Perfect answer. I assume as you do not mention gravity, that the sun’s gravitational attraction , max at the perihelion, is not contorting the comet? Sent from my Windows Phone

Dear Chandra:  In my student days I would not have had to ask you this question. But I have not enough time to relearn orbit mathematics even though I have “scanned” this : http://en.wikipedia.org/wiki/Orbit

I am thinking about the force exerted on a orbiting comet as it approaches its perihelion. I assume the force is maximum at the perihelion.

As 67P’s perihelion is further out from earth (between earth and mars) I was wondering what the “pressure” really was on the comet? Are you sure this is what is causing the geysers to increase? Somewhere you wrote/implied that the geyser-causing pressure might be nuclear?