An artist's illustration of an Earth-like planet. The search for planets that are similar to Earth is one of NASA's main goals. Many planets have already been discovered orbiting other stars, but so far only larger planets (the size of Jupiter or larger) have been found. New missions are being planned by NASA which will be able to detect smaller Earth-sized planets. Some of these missions will also try to detect signs of life on these planets by studying emissions in their atmospheres.
'Fifty planets' could have life
By Helen Briggs
1 April, 2004
Astronomers estimate about half the planetary systems so far discovered in our galaxy could contain Earth-like worlds.
And they say that space telescopes will be capable of observing these planets and investigating them to see if they support life in about 15 years' time.
Scientists have recently discovered more than 100 stars other than our Sun with planets circling about them.
But they are all giant planets like Jupiter that cannot sustain life.
Planets more like the Earth should, in theory, exist too. But they are too small to be seen using current technology.
Research work by the UK's Open University suggests there are perhaps 50 or so of these small, rocky bodies on which there is liquid water and possibly life.
"We would certainly expect them to be something like Earth in size and in mass, to have a reasonable atmosphere; they'll have oceans and continents, they'll be potential abodes of life, but the big question is - has there actually been life there?" OU astronomer Professor Barrie Jones told BBC News Online.
His team used computer modelling to calculate the likely number of habitable planets, based on what we know about how planets form and the conditions needed for life.
The planets would exist in what is sometimes referred to as the "Goldilocks" zone, a region set back from the parent star where it is neither too hot for liquid water, nor too cold.
By launching "Earths" into a variety of orbits in this zone and following their progress with the computer model, the small planets have been found to suffer a variety of fates.
Read more: http://news.bbc.co.uk/2/hi/sci/tech/3588721.stm
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