Comets – Astronomy Talk


15th July 2014

This talk was given by the Chairman.
The talk started with the question: what are comets? Usually called dirty snowballs, the examples looked at their structure including their albedo, nucleus and tails.
They originate far out in the solar system, and the talk looked at the solar system’s formation and the subsequent location of comets beyond the planetary realm. They are now found in the Kuiper belt, the Scattered Disc, and especially in the Oort cloud
We looked at what we see nearer to home, including Centaurs between Jupiter and Neptune. Most inner solar system comets are divided into 2 families, short-period and longperiod. There are also some main belt comets in the out reaches of the asteroid belt with fairly circular orbits.
We then looked at a bit of history, at myths and legends, which are mostly of woe, including Europe and China. Aristotle’s view of their origin and refutations of this were covered as well.
Some say the water on Earth comes from comets, but it’s perhaps more likely it comes from icy asteroids, based on isotopic ratios of hydrogen and deuterium.
As an origin of life the panspermia theory promotes comets as the vectors: the Wickramasinghe/Hoyle theory.
Lastly we looked at collisions with Earth and the energy yields from those, including Chicxulub and Tunguska. We looked at ways to divert a comet. Lastly it seems there may well be many invisible ex-comets with very low albedos, which could strike the Earth with no notice!