Directly observing planets outside our solar system - called exoplanets - is almost impossible because they are washed out by the glare of the parent star. For this reason astronomers have largely relied on indirect methods that observe the effects of the planets on their parent stars instead of the planets themselves. Such indirect detection methods have helped take the number of exoplanets discovered so far to more than 350, but determining whether signs of life exist on a planet that can’t actually be seen presents a problem. Astronomers from the Instituto de Astrofisica de Canarias (IAC) have found a solution.
When a planet passes in front of its parent star, part of the starlight passes through the planet’s atmosphere. This is called the transmission spectrum and it provides vital information about the planet itself including information about the constituents of the atmosphere. While the team wasn’t able to use this exact method to look at the Earth’s atmosphere, they were able to measure the transmission spectrum of the Earth for the first time by observing light reflected from the Moon towards the Earth during a lunar eclipse.
The spectrum not only contained identifiable signs of life, but these signs were unmistakably strong. It also contained unexpected molecular bands and the signature of the earth ionosphere. These results provide astronomers with an idea of what the transmission spectrum of an inhabited planet looks like, so we now have a much better idea of how to find and recognize Earth like planets outside our solar system where life may be thriving.
The past two decades have witnessed the discovery of hundreds of exoplanets, and the discovery of many Earth-size planets are expected in coming decades. By confirming that observing the transmission spectrum is an effective way to gather information about the biological processes taking place on a planet, the team has vastly improved the chances of finding alien life on exoplanets.
The team from the Instituto de Astrofisica de Canarias (IAC) used the Science and Technology Facilities Council’s (STFC) William Herschel Telescope (WHT) on La Palma and the Nordic Optical Telescope (NOT) to conduct their research, which is published in the June 11 edition of Nature.