Lesson 55
From the earth: Greetings
Which life forms are most likely to develop on a distant planet?
Recent developments in astronomy have made it possible to detect planets in our own Milky Way and in other galaxies.
This is a major achievement because, in relative terms, planets are very small and do not emit light.
Finding planets is proving hard enough, but finding life on them will prove infinitely more difficult.
The first question to answer is whether a planet can actually support life.
In our own solar system, for example, Venus is far to hot and Mars is far too cold to support life.
Only the Earth provides ideal conditions, and even here it has taken more than four billion years for plant and animal life to evolve.
Whether a planet can support life depends on the size and brightness of its star, that is its 'sun'.
Imagine a star up to twenty times larger, brighter and hotter than our own sun.
A planet would have to be a very long way from it to be capable of supporting life.
Alternatively, if the star were small,
the life-supporting planet would have to have a close orbit round it and also provide the perfect conditions for life forms to develop.
But how would we find such a planet?
At present, there is no telescope in existence that is capable of detecting the presence of life.
The development of such a telescope will be one of the great astronomical projects of the 21st century.
It is impossible to look for life on another planet using earth-based telescopes.
Our own warm atmosphere and the heat generated by the telescope
would make it impossible to detect objects as small as planets.