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article image'Extremely Large Telescopes' could detect oxygen on exoplanets

By JohnThomas Didymus     Feb 20, 2013 in Science
New telescopes such as the European Extremely Large Telescope (E-ELT) soon to come into use will be able to hunt for life by determining whether the atmospheres of small terrestrial exoplanets contain oxygen or other biomarker gases.
According to a new study published in The Astrophysical Journal, entitled "Finding Extraterrestrial Life Using Ground-based High-Dispersion Spectroscopy," the European Extremely Large Telescope (E-ELT) to be set up in the next decade on a Chilean mountain top, Cerro Armazones, will be able to determine whether the gases considered essential for life as we know it on Earth are present in the atmosphere of distant exoplanets.
According to Phys.org, astronomers in the Netherlands say that new ground-based telescopes could be used to determine whether small terrestrial exoplanets have biomarker gasses in their atmospheres, and consequently the likelihood that some form of life exists on them.
The researchers suggest that it could be possible to use newly developed methods to distinguish atmospheric gases on exoplanets from gases in the Earth's atmosphere while using ground-based telescopes to observe the distant exoplanets.
The importance of being able to detect biomarker gases or atmospheric gases in "strong chemical disequilibrium" in their exoplanetary environment arises from the fact that such gasses may be indicators of life.
For instance, on planet Earth, we have abundant atmospheric oxygen gas only because of the photosynthetic activity of plants and some bacteria. Finding oxygen or some other biomarker gas such as methane on an exoplanet could be suggestive of life as we know it on that planet.
According to the study abstract, "Atmospheric compounds in strong chemical disequilibrium would point to large-scale biological activity just as oxygen and methane do in the Earth's atmosphere."
However, detecting the atmospheric constitution of exoplanets using ground-based telescopes has presented daunting challenges to scientists because telescopes located within the Earth's atmosphere must deal with distortions arising from having to peer into space though Earth's atmosphere. The technical challenges led many scientists to believe that accurate observations of the atmospheres of exoplanets will have to wait until dedicated space-based telescopes are built and set up. However, hopes that it would be possible to launch dedicated telescopes to search for biomarker gases in exoplanet atmospheres were scuttled with the "cancellation of both the Terrestrial Planet Finder and Darwin missions."
Now that it is unlikely that a dedicated telescope that could used to search for extraterrestrial life will be launched in the next 25 years, the research scientists suggest an alternative approach. They suggest that it may be possible to detect biomarker gasses by taking the spectral signatures of gases in the light coming from an exoplanet, while taking into account the red/blue shift of Doppler effect in the spectral lines arising from the motion of the planet relative to the Earth.
According to New Scientist, current telescopes can only determine the atmospheric makeup of big astronomical bodies such a gaseous planets called "gas giants" using spectral analytic techniques. Gas giants are large planets made up of liquids and gases which scientists are currently able to study using ground-based telescopes that look for the spectral signatures of gases present in their atmosphere.
According to the study lead author Ignas Snellen of Leiden Observatory in the Netherlands, "We do this now for Jupiter-sized planets."
However, the atmospheres of smaller rocky or terrestrial planets similar to our Earth are harder to detect with telescopes currently in use because they find it difficult to distinguish effects arising from the motion of our Earth's oxygen-rich atmosphere from those arising from the motion of the distant planet under observation.
However, Snellen and his colleagues say that these technical difficulties may be overcome using the European Extremely Large Telescope (E-ELT).
The telescopes will be equipped with a 39-meter main mirror that allows for observation of distant stars and galaxies with higher resolution. Under such conditions, it would be possible by taking account of the Doppler wavelength band shift effect to distinguish Earth's atmospheric constituents from those of the distant planet under investigation.
New Scientist notes that the researchers say technical difficulties will arise from the fact, depending on the shape of its orbit and the size of the star, that a planet will have to pass between its parent star and the observing telescope several times for astronomers to gather sufficient information to determine its atmospheric constituents. The scientists said it could take between four years and four centuries to gather enough data to characterize the atmosphere of a single planet right.
Raw Story reports that Jack O’Malley-James at the University of St. Andrews at Fife, U.K. warned that finding a planet rich, for instance in atmospheric oxygen, will not guarantee it holds life because organisms on alien planets may be able to evolve in adaptation to diverse atmospheric conditions.
We find such diversity on planet Earth in the case of deep sea hydrothermal vents that support exotic anaerobic microbes in oxygen-free environments. Scientists have also found bacteria surviving at "black smoker" vents where they use no sunlight energy but derive their energy from the sulfur boiling out of fissures in the sea floor under temperatures that may reach to 700 degrees Fahrenheit.
Researchers also point out that scientists are placing too much emphasis on the use of big mirror telescopes. They suggest use of several smaller "flux bucket" scopes that "collect as much light as possible" but are "not able to produce the same detailed images as the bigger observatories." They explain that such devices have the advantage of allowing for "long-term research models needed for observing exoplanets."
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