|Posted by Web Master on September 6, 2013 at 12:35 AM|
Planet hunters keep finding distant worlds that bear a resemblance to Earth. Some of the thousands of exoplanet candidates discovered to date have similar sizes or temperatures. Others possess rocky surfaces and support atmospheres. But no world has yet provided an unambiguous sign of the characteristic that still sets our pale blue dot apart: the presence of life.
That may be about to change, says exoplanet expert Sara Seager of the Massachusetts Institute of Technology in Cambridge. Upcoming NASA missions such as the Transiting Exoplanet Satellite Survey (TESS) and the James Webb Space Telescope, both due to launch around 2018, should be able to find and characterize Earth-like planets orbiting small stars.
Spotting signs of life on those planets will be possible because of progress in detecting not only planets, but their atmospheres as well. When a planet passes in front of its host star, atmospheric gases reveal their presence by absorbing some of the starlight. Oxygen, water vapor or other gases that do not belong on dead worlds could very well provide the first evidence of life elsewhere. [5 Bold Claims of Alien Life]
Exoplanet expert Sara Seager of the Massachusetts Institute of Technology.
In 1961, astronomer Frank Drake developed an equation that summarizes the main factors to contemplate in the question of radio-communicative alien life. These factors include the number of stars in our galaxy that have planets and the length of time advanced alien civilizations would be releasing radio signals into space.
Instead of aliens with radio technology, Seager has revised the Drake equation to focus on simply the presence of any alien life. Her equation can be used to estimate how many planets with detectable signs of life might be discovered in the coming years. Presented at a meeting earlier this year, the Seager equation looks like this:
N = N*FQFHZFOFLFS
N = the number of planets with detectable signs of life
N* = the number of stars observed
FQ = the fraction of stars that are quiet
FHZ = the fraction of stars with rocky planets in the habitable zone
FO = the fraction of those planets that can be observed
FL = the fraction that have life
FS = the fraction on which life produces a detectable signature gas
Focusing on M stars, the most common stars in our neighborhood that are smaller and less luminous than the sun, Seager plugged in values for each term. Her calculation suggested that two inhabited planets could reasonably turn up during the next decade.