The search for ET just got easier

June 10, 2009

Astronomers using the Science and Technology Facilities Council's (STFC) William Herschel Telescope (WHT) on La Palma have confirmed an effective way to search the atmospheres of planets for signs of life, vastly improving our chances of finding alien life outside our solar system.

The team from the Instituto de Astrofisica de Canarias (IAC) used the WHT and the Nordic Optical Telescope (NOT) to gather information about the chemical composition of the Earth's atmosphere from sunlight that has passed through it. The research is published today (11th June) in Nature.

When a planet passes in front of its parent star, part of the starlight passes through the planet's atmosphere and contains information about the constituents of the atmosphere, providing vital information about the planet itself. This is called a transmission spectrum and even though astronomers can't use exactly the same method to look at the Earth's atmosphere, they were able to gain a spectrum of our planet by observing light reflected from the Moon towards the Earth during a lunar eclipse. This is the first time the transmission spectrum of the Earth has been measured.

The spectrum not only contained signs of life but these signs were unmistakably strong. It also contained unexpected molecular bands and the signature of the earth ionosphere.

Enric Palle, lead author of the paper, from the Instituto de Astrofisica de Canarias, said, "Now we know what the transmission spectrum of a inhabited planet looks like, we have a much better idea of how to find and recognize Earth like planets outside our solar system where life may be thriving. The information in this spectrum shows us that this is a very effective way to gather information about the biological processes that may be taking place on a planet."

Pilar Montañes-Rodriguez, from the Instituto de Astrofisica de Canarias, added, "Many discoveries of Earth-size planets are expected in the next decades and some will orbit in the habitable zone of their parent stars. Obtaining their atmospheric properties will be highly challenging; the greatest reward will happen when one of those planets shows a spectrum like that of our Earth."

The past two decades have witnessed the discovery of hundreds of exoplanets (planets beyond our ). Ambitious missions, ground and space based, are already being planned for the next decades, and the discovery of Earth-like planets is only a matter of time. Once these are found, techniques like transmission spectra will be invaluable to their further exploration.

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council (STFC), said, "This new transmission spectrum is good news for future upcoming ground and space based missions dedicated to the search for life in the Universe. The UK is committed to cutting edge science and UK owned facilities like the WHT are helping to make many groundbreaking discoveries and expand our knowledge of the Universe. Not only do these results improve our knowledge of our own planet but we now have an effective way to search for life on the increasing number of exoplanets being found by astronomers."

Source: Science and Technology Facilities Council (news : web)

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4.5 / 5 (2) Jun 10, 2009
Good news to be sure, but I would like to know exactly what causes the variance in our transmission spectrum.

Based on exactly what causes this variance, we could be potentially limited to inhabited planets that are around our own level of development. Yes this is still a major finding regardless, but if the differences are caused by an industrial level of development, planets that are majorly ahead of us, or substancially behind us may not be as simple to detect.

Can anyone site better examples of exactly what these variances are?
5 / 5 (2) Jun 10, 2009
It's not a "variance"... It's spectroscopy (analysis of spectroscopic emissions). Basically, you can pinpoint all the elements by which wavelength in the spectrum they absorb - just look at a spectrum of light that has passed through any atmosphere and you will find dark bands running vertically along the spectrum blocking various wavelengths... these correspond to individual elements. For instance, when taking a spectroscopic measurement of the Sun, you'll find the bands of Hydrogen and Helium blocked out pretty easily.

Here's a pretty good run down (pay attention to the bright line and dark line spectrum ideas): http://spiff.rit....tra.html

Anywho, if able to spectroscopically analyze light from another world (very, VERY, difficult), we would look for non naturally occurring elements in the atmosphere, such as Oxygen, Methane, etc. which are very good indicators of life as there are very few other things that produce these gases in large scale other than lifeforms (that we know of).

i.e. There wouldn't be any oxygen in our atmosphere if trees weren't out there passing gas all day!

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