Lecture Notes:

• 1. Comet Hale-Bopp, perhaps the most spectacular comet since 1811! Probably better than Halley’s comet or Hyakutake.Halley had a nucleus which measured 15 km by 8 km; Hyakutake was perhaps 3 km in diameter, but Hale-Bopp may be 40 km in diameter. Comets are great sights but are also of interest because they occasionally collide with the earth with devastating results. The dinosaurs were probably zapped by a comet that collided with the earth 65 million years ago which apparently produced the great crater in the Yucatan peninsula known as Chicxulub, 180 km in diameter. The "great dying "of the Permian extinction event at 250 million was also apparently due to a comet collision. Geologists in Australia have just recently discovered shocked quarts dating to that time, indicative of such a collision.

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• 2. Europa and other sights transmitted to us form the Galileo spacecraft. Europa may have a moon-wide layer of cracked ice overlying an ocean of water. It is another possible place for life in the solar system.

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• 3. Mars meteorite with life. Two meteorites have evidence (still controversial) of life dating from 3.6 billion years (just after Mar’s magma ocean cooled) and 180 million years, quite recent as planets go, ;which may indicate that some form of primitive life is still there.

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• 4. Planets around distant stars: 4 of these planets have been discovered during the last year. They are all large, about the size of Jupiter, and lie closer to their respective stars than Mercury to the sun. They may have been formed further out and gradually spiraled in due to a friction with dust in space.

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• 5. The spacecraft Clementine detected ice in a dark crater on the southern pole of the moon, that may have been deposited there by a comet some time in the past.