Billions Of Earth-Like Planets In Our Galaxy
It is worth remembering that our galaxy alone has billions of Earth-like planets, and these earths are “[not only] probably habitable but they probably are also going to be inhabited”
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Galaxy has ‘billions of Earths’
There could be one hundred billion Earth-like planets in our galaxy, a US conference has heard.
Dr Alan Boss of the Carnegie Institution of Science said many of these worlds could be inhabited by simple lifeforms.
He was speaking at the annual meeting of the American Association for the Advancement of Science in Chicago.
So far, telescopes have been able to detect just over 300 planets outside our Solar System.
But, based on the limited numbers of planets found so far, Dr Boss has estimated that each Sun-like star has on average one “Earth-like” planet.
This simple calculation means there would be huge numbers capable of supporting life.
“Not only are they probably habitable but they probably are also going to be inhabited,” Dr Boss told BBC News. “But I think that most likely the nearby ‘Earths’ are going to be inhabited with things which are perhaps more common to what Earth was like three or four billion years ago.” That means bacterial lifeforms.
Source: http://news.bbc.co.uk/2/hi/7891132.stm
The caption below was written in November 2004.
Other Earths
So, after having compiled a bestiary of exotic planets, many the size of Jupiter and locked in a deadly embrace with their star, what are the chances of the planet-hunters identifying rather smaller, sedate rocks upon which life might actually get the chance to evolve? It’s not as if these planets are likely to exist in minute numbers: current estimates [Using the Drake Equation] border on there being 30 billion terrestrial planets in our Galaxy alone [this is an article from 2002]. The odds of finding such planets lengthen a lot when one considers that these planets would have longer years and cause much smaller wobbles in their star’s position.
The odds shorten again the longer we look for these planets. Hot Jupiters tend to get found simply because the radial velocity method is most sensitive to their kind. It’s only now that smaller planets are being found, although none of them are likely to harbour life. Adopt a different method of detection, and we might start to see terrestrial planets, instead of inferring their presence.
This is precisely what the Terrestrial Planet Finder (TPF) telescope is designed to do. This instrument comprises four space-based telescopes flying in formation. Their light is combined in such a way as to vastly increase resolution. One of the indicators that TPF will be looking for is the presence of elemental oxygen in a planet’s atmosphere. All oxygen in our atmosphere is there because of photosynthetic organisms: plants and cyanobacteria. Oxygen is therefore a key signature of life6.
TPF is not due to fly until 2015 at the earliest. In the meantime, Earth-based telescopes will get bigger and better, and astronomers will be able to observe for longer wobbles than they currently can. Even if we can’t see the little green men yet, we’ll have a much better idea of where they might live.
Source: H2G2 extrasolar planet hunting














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