Detecting Earth-like planets harder than previously thought

March 20th, 2009 - 12:29 pm ICT by ANI  

Washington, March 20 (ANI): A new study by scientists has determined that it would be much more difficult to detect Earth-sized worlds that are habitable than previously believed.
The study, by Lisa Kaltenegger (Harvard-Smithsonian Center for Astrophysics) and Wesley Traub (Jet Propulsion Laboratory), examined the ability of JWST (James Webb Space Telescope) to characterize the atmospheres of hypothetical Earth-like planets during a transit, when part of the light of the star gets filtered through the planet’’s atmosphere.
They found that JWST would be able to detect certain gases called biomarkers, such as ozone and methane, only for the closest Earth-size worlds.
“We”ll have to be really lucky to decipher an Earth-like planet’’s atmosphere during a transit event so that we can tell it is Earth-like,” said Kaltenegger. “We will need to add up many transits to do so - hundreds of them, even for stars as close as 20 light-years away,” she added.
“Even though it’’s hard, it will be an incredibly exciting endeavor to characterize a distant planet’’s atmosphere,” she further added.
In a transit event, a distant, extrasolar planet crosses in front of its star as seen from Earth. As the planet transits, gases in its atmosphere absorb a tiny fraction of the star’’s light, leaving fingerprints specific to each gas.
By splitting the star’’s light into a rainbow of colors or spectrum, astronomers can look for those fingerprints.
Kaltenegger and Traub studied whether those fingerprints would be detectable by JWST.
Kaltenegger and Traub first considered an Earth-like world orbiting a Sun-like star.
To get a detectable signal from a single transit, the star and planet would have to be extremely close to Earth.
The only Sun-like star close enough is Alpha Centauri A. No such world has been found yet, but technology is only now becoming capable of detecting Earth-size worlds.
The study also considered planets orbiting red dwarf stars. Such stars, called type M, are the most abundant in the Milky Way - far more common than yellow, type G stars like the Sun.
They are also cooler and dimmer than the Sun, as well as smaller, which makes finding an Earth-like planet transiting an M star easier.
An Earth-like world orbiting a star like the Sun would undergo a 10-hour transit once every year. Accumulating 100 hours of transit observations would take 10 years.
In contrast, an Earth orbiting a mid-sized red dwarf star would undergo a one-hour transit once every 10 days. Accumulating 100 hours of transit observations would take less than three years.
“Nearby red dwarf stars offer the best possibility of detecting biomarkers in a transiting Earth’’s atmosphere,” said Kaltenegger. (ANI)

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