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[ti:From the Earth: Greetings]
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[00:01.45]Lesson 55
[00:04.07]From the earth: Greetings
[00:13.62]Which life forms are most likely to develop on a distant planet?
[00:20.55]Recent developments in astronomy have made it possible to detect planets in our own Milky Way and in other galaxies.
[00:29.22]This is a major achievement because, in relative terms, planets are very small and do not emit light.
[00:37.67]Finding planets is proving hard enough, but finding life on them will prove infinitely more difficult.
[00:45.35]The first question to answer is whether a planet can actually support life.
[00:50.96]In our own solar system, for example, Venus is far to hot and Mars is far too cold to support life.
[01:00.55]Only the Earth provides ideal conditions, and even here it has taken more than four billion years for plant and animal life to evolve.
[01:11.42]Whether a planet can support life depends on the size and brightness of its star, that is its 'sun'.
[01:19.70]Imagine a star up to twenty times larger, brighter and hotter than our own sun.
[01:26.81]A planet would have to be a very long way from it to be capable of supporting life.
[01:32.84]Alternatively, if the star were small,
[01:35.61]the life-supporting planet would have to have a close orbit round it and also provide the perfect conditions for life forms to develop.