Super-Earths 'in the billions'
By Jonathan Amos for The BBC
28 March 2012
There could be many billions of planets not much bigger than
Earth circling faint stars in our galaxy, says an international team of
astronomers. The estimate for the number of "super-Earths" is based
on detections already made and then extrapolated to include the Milky Way's
population of so-called red dwarf stars. The team works with the high-precision
Harps instrument. This is fitted to the 3.6m telescope at the Silla Observatory
in Chile .
Harps employs an indirect method of detection that infers the existence of
orbiting planets from the way their gravity makes a parent star appear to
twitch in its motion across the sky. "Our new observations with Harps mean
that about 40% of all red dwarf stars have a super-Earth orbiting in the
habitable zone where liquid water can exist on the surface of the planet,"
said team leader Xavier Bonfils from the Observatoire des Sciences de l'Univers
de Grenoble, France. "Because red dwarfs are so common - there are about
160 billion of them in the Milky Way - this leads us to the astonishing result
that there are tens of billions of these planets in our galaxy alone."
The Harps team came up with its numbers after surveying 102
carefully chosen red dwarfs, which are dimmer and cooler than our Sun. The group
found a total of nine super-Earths (which are defined as planets with one to 10
times the mass of the Earth), with two judged to be orbiting inside their
stars' habitable zones. Putting all its data together, including observations
of stars that did not have planets, the team was able to produce an estimate
for how common different sorts of planets are around red dwarfs. This
assessment suggests super-Earths in the habitable zone occur in 41% of cases, with a range from 28% to 95%.
Given how many red dwarf stars there are in close proximity
to the Sun, it means there could be perhaps 100 super-Earth planets in the
habitable zones of stars that are less than about 30 light-years distant. "The habitable
zone around a red dwarf, where the temperature is suitable for liquid water to
exist on the surface, is much closer to the star than the Earth is to the
Sun," commented co-researcher Stephane Udry from the Geneva Observatory.
"But red dwarfs are known to be subject to stellar eruptions or flares,
which may bathe the planet in X-rays or ultraviolet radiation, and which may
make life there less likely."
3 comments:
Everything we know makes life very likely. Which is one more reason why people should take Fermi's paradox a bit more seriously. If they aren't here (and didn't come here millions of years ago when the earth was bathed in green plants and had an atmosphere), what's up?! The various explanations that people put forth make no sense at all. The only thing that I can think of is that for advanced cilizations who can do pretty much whatever they want, little pieces of green real estate just isn't as valuable as we imagine.
Fermi's Paradox is a good one I admit. I've come across a few answers (or at least attempted answers) to it - none of which are hugely convincing. It is still rather odd though. The more we find out about our Galaxy the more likely life in it becomes... yet, where is everyone?
I might do a 'Thinking About' on this in the (near) future.
Please do! I think that all the typical speculations about advanced civilizations blowing themselves up and whatnot are completely off the mark. When dealing with millions of possible civilizations, one can assume that at least one has gotten things right and is as stable as an Egyptian dynasty or a Confucian monarchy. The harder part is imagining what exactly the Earth has to offer. I think the whole idea of resources (gas etc.) is ridiculous (one nearby Jupiter would dwarf the resources of Earth). The only thing I can think of is genetic diversity or perhaps even cultural diversity (in which case, there may be an advantage in observing Earth in a way that keeps civilization fairly unpreturned.)
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