Posted: 06 Aug 2014 01:00 PM PDT
Astronomers are standing on a
"great threshold" of space exploration that could see evidence of
extra-terrestrial life being discovered in the next 20 years, an expert claims.
Life beyond the Earth seems
"inevitable" given the immensity of the universe, according to US
planetary scientist Dr Sara Seager.
In the coming decades, chemical
fingerprints of life written in the atmospheres of planets orbiting nearby
stars could be found by the next generation of space telescopes.
Writing in the journal
Proceedings of the National Academy of Sciences, Dr Seager, from the
Massachusetts Institute of Technology (MIT), said: "We can say with
certainty that, for the first time in human history, we are finally on the
verge of being able to search for signs of life beyond our Solar System around
the nearest hundreds of stars."
Astronomers now know that
statistically, every star in our galaxy, the Milky Way, should have at least
one planet, and small rocky worlds like the earth are common.
Dr. Sara Seager
"Our own galaxy has 100
billion stars and our universe has upwards of 100 billion galaxies - making the
chance for life elsewhere seem inevitable based on sheer probability," Dr
Seager said.
In the next decade or two, a
handful of "potentially habitable" exoplanets will have been found
with atmospheres that can be studied in detail by sophisticated space
telescopes.
The first of these "next
generation" telescopes will be the American space agency NASA's James Webb
Space Telescope (JWST) due to be launched in 2018.
It will be able to analyse the
atmospheres of dozens of "super-earths" - rocky planets somewhat
larger than Earth - including several that could harbour life.
Studying a planet's atmosphere
for signs of life involves capturing starlight filtering through its gases.
Different elements absorb
different wavelengths of light, providing information about the atmosphere's
make-up.
Living things, from bacteria to
large animals, are expected to produce "biosignature" gases that
could be detected in a planet's atmosphere. They include oxygen, ozone, nitrous
oxide, and methane.
The problem faced by scientists
is that some of these, such as methane, can be generated by geological
processes as well as life.
The likelihood of "false
positives" could be reduced by searching for rarer biosignature gases more
closely tied to living systems, such as dimethyl sulphide (DMS), and
methanethiol, Dr Seager said.
But she pointed out that
observations using telescopes such as the JWST, which will focus on backlit
"transiting" planets that happen to passing in front of their parent
stars, will be limited.
Maximising the chances of finding
evidence of extraterrestrial life will require a technological leap to methods
of directly imaging large numbers of exoplanets.
Such an undertaking is daunting,
given that directly imaging an earth-like exoplanet is equivalent to picking
out a firefly in the glare of a searchlight from thousands of kilometres away.
Yet two techniques now under
development could make direct imaging of earth twins possible.
One involves specialised optics
to block out interfering starlight and reveal the presence of orbiting exoplanets.
The other is the "starshade" - an umbrella-like screen tens of metres
in diameter placed tens of thousands of kilometres in front of a space
telescope lens.
No comments:
Post a Comment