destroying all life there. But frozen Titan will be warmed to a surface temperature of -70ºC, which will create oceans of water mixed with ammonia. Ralph Lorenz and his colleagues at the University of Arizona’s Lunar and Planetary Laboratory, Tuscan, predict that this process could give rise to life (Hecht, 1997: 28). The Sun’s red giant phase will last for several hundred million years, which is longer than it took for life to evolve on Earth. But Titan might not only be a cradle for life; it could well become a refuge for those who are fortunate enough to escape from Earth. If Lorenz’s hypothesis is correct, then other red giant suns could support life on former frozen planets.

Uranus

Uranus is twice as far as Saturn from the Sun, and has an 84-year orbit. It has a substantial atmosphere, consisting mainly of molecular hydrogen, and possibly ammonia or methane, but its surface is hidden by clouds and the density of its atmosphere. It is a large gaseous planet which is an extremely unlikely site for living phenomena, although it is always possible that the gas giants, Uranusand Neptune, could support micro-organisms, but such thoughts are highly speculative. Uranus has seventeen known satellites, the last two discovered in October 1997. They range in size from diameters of 50 to 100 metres, and probably consist of icy and rocky materials, but are too small to retain an atmosphere.

Neptune

The planet Neptune is a gas giant similar to Uranus. Like the other gas planets, Jupiter, Uranus and Saturn, its atmosphere consists largely of hydrogen with traces of helium and other chemicals and the  planet produces considerable internal heat. It has no surface beneath its atmosphere. Neptune has two satellites and possibly a third. The two known satellites are Triton and Nereid, so named after the servants of Neptune. Triton is volcanic and may possess an atmosphere of nitrogen and methane. It is extremely cold with a temperature of -223ºC, and is a very inhospitable place.

Pluto

The planetary status of Pluto has been questioned: it is very small and more typical of the medium-sized satellites of the outer planets. One theory is that it is a planetesimal, left over from the creation of the solar system. Another theory suggests that it is an escaped satellite of Neptune. Spectroscopic observations revealed in 1976 that it has an icy composition, with frozen methane, and its temperature is about -223ºC. Its desolate frozen landscape is pock-marked with craters.

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The asteroids

There has been speculation that asteroids could sustain colonies from an advanced technological culture (Papagiannis, 1978) but only exploration would settle this matter decisively. It has been argued that some of life’s precursors are to be found in the asteroids as several meteorites bearing organic compounds may come from the asteroids.

Comets

There are about 600 comets in the solar system; their total mass is only about 0.1 the mass of the Earth so they are not likely to retain an atmosphere. However, their total surface area is 1,000 times greater than the size of the Earth. As they contain carbon, nitrogen, oxygen and hydrogen, they could provide habitable sites for some kinds of life. Freeman J. Dyson (1973) argued that  too much attention has been given to searches for planetary life and not enough to comets. The home for really big technology, associated with supercivilizations (or ‘Dyson civilizations’), is more likely to be on comets, argues Dyson. Whereas planets may be important for the generation of life, supercivilizations may have out-grown them. Now if comets are distributed throughout the galaxy, some of them could be habitable oases, which could shorten the distance between contact points. If such an idea is plausible it would certainly encourage a re-assessment of ideas about ET interstellar travel. Dyson also suggests that his hypothesis can be tested by searching for high levels of infrared radiation in the vicinity of comets. However, it is always possible that very advanced civilizations might not use up so much energy and their presence on comets would not be detectable.

Colonizing the solar system

Space travel, it has been argued, is a now or never affair (Breuer, 1982), as we are using up the necessary material resources. There are proposals to mine asteroids. Space Dev is an American exploration company that wants to stake its claim to an asteroid, which is intended to be mined for its minerals when the technology becomes available (Kleiner, 1997: 18). This raises legal problems, as international treaties prevent nations from staking a claim to heavenly bodies. But the status of private companies is not that clear in this field. It has been pointed out that in about 200 years there will not be the fossil and metallic raw material for spaceships and space stations (Breuer, 1982: 256). If work is not undertaken soon to extract material from the Moon, it will be too late to exploit the Moon or the asteroids, as there will not be the material left on Earth to create the rockets capable of lifting a minimum of 2,000 tonnes of implements and a nuclear reactor to the Moon. The distances within the solar system are daunting, not only in terms of material resources, but in terms of the psychological problems encountered in long periods in space.

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