Firstly, there are several lessons to be learned from astronomy and space science for our life on Earth. In science, learning from extreme cases usually gives one insights into the ordinary situation; in medicine, we often learn about diseases and treatments from studying other species. So, in the case of Earth's climate and history, we can learn from other planets.

The danger of all-out nuclear war, mercifully now receding after the end of the Cold War, was unique in that, alone of all the perils we face, it endangered not just civilization, but even our biological existence. Other threats, like Ebola virus plagues, global warming, or even a new Ice-Age, may destroy civilization, perhaps irreversibly, but would not wipe out the whole race. The reason given in the mid 1980's was the phenomenon of nuclear winter. In this picture, the exchange of more than a certain number of bombs (thought to be 100-200 by many authorities), would cause so much dust and smoke to enter the

The US House of Representatives set up a committee in 1992 to look at ways of detecting more of these earth crossing asteroids, in a programme called Space Watch; over the next 20 years, some 75% of the one kilometre sized objects are expected to be found. However, long period comets will be unpredictable, while chaos theory shows that, even if an orbit is determined, the object can drift in as little as ten years, owing to its small size. The Space probe NEAR (Near Earth Asteroid Rendezvous) will take our first look at 433 Eros - a large Earth crossing asteroid - in 1999.

Asteroids, considered by some astronomers as of little interest, have been of vital relevance to Earth since the beginning, and will be even more so in the future. Some small carbonaceous Near Earth asteroids are believed to be the remains of comets which have blown off their gases and water after several trips around the sun, so this discussion is equally relevant to comets.

Secondly, we know that life began 3.6 to 3.8 billion years ago, but that the bombardment of the young hot earth by mini-planets which formed the earth only slowed down some 3.9 billion years ago; so that life got started very quickly. The possible early origin of life on Mars, and maybe Europa, if confirmed , would add credence to the idea that Life's seeds originate in primordial propylids ( accretion discs on their way to planetary system formation), and hence that simple life, at least, is widespread, requiring only good planetary soil for its germination. Intelligence , is of course another matter! It is easier to believe that life received an input from the heavens, or, to put it more poetically, that Mother Earth was fertilized by sperm-like comets. What could be more natural?

By the year 1800, astronomers had reached an understanding of Newton's new cosmos, and were looking for underlying laws explaining the positions and birth of the planets. The mathematicians Titius and Bode related all the planets then known in a simple formula; using 1 Astronomical Unit AU = 150 million kilometres, or Earth's distance from the Sun, the planets Mercury to Saturn stood at 0.4, 0.7, 1, 1.6, 5.2, 10.0, and 19.6 units from the Sun. Apart form Mercury, which is very eccentric, the distance between the planets doubles as you move outwards. This agrees well with the reality, except for the gap where 2.8 should be. We now know that this "Law" is not true, and that Neptune and Pluto break it completely - but in the 1780's the discovery of Uranus at just the right distance gave it support. The gap between Mars and Jupiter led to a search for the "missing planet", and, on New Year's Day 1801, it was found. However, it was very small, and did not show a disc in the telescopes of the day. Because it looked like a star - a point of light - but moved slowly like a planet, it was called an "asteroid", or star - like object. The name has stuck, and the first was called Ceres. Pallas, Juno, and Vesta were found in the next few years, and , by 1980 several thousand wer

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Approximate Word count = 2030
Approximate Pages = 8 (250 words per page double spaced)