Exoplanet research in recent years has revealed thousands of planets orbiting distant stars, but simply identifying a planet's existence is far simpler than revealing that planet's properties. Presumably, a planet that can support life would be somewhat similar to Earth: made of rock instead of gas, close enough to its parent star to be within the "habitable zone" and having an atmosphere composed of an excretable gas such as oxygen or methane.
In order to discover these qualities, NASA has proposed the construction of a space-based telescope known as the Advanced Technology Large Aperture Space Telescope (ATLAST), some 2,000 times more sensitive than the orbiting Hubble telescope. If the proposal is approved, NASA predicts that ATLAST could be completed between 2025-2035.
But Dr. Matteo Brogi, with the University of Colorado, believes that exoplanets can be examined for alien life with instrumentation already under construction. This would be done through the combination of techniques available now, including high-resolution spectroscopy and direct imagining.
High-resolution spectroscopy finely details the wavelengths that make up light. Chemicals leave "fingerprints" on light, so, for instance, light coming from our Earth would reveal the presence of oxygen and methane (both of which are produced by life forms) to a spectroscopic image. The central issue with using a spectroscope to identify the atmosphere of an exoplanet, according to a Space.com article, is that "trying to see the light from a planet (which is fairly dim) when it is orbiting right next to a star (which is incredibly bright) is like trying to see the glow of a firefly against a backdrop of 1,000 stage spotlights (which would be difficult.)"
Direct imaging is reminiscent of photography, in which a detailed image of a exoplanet is created by a telescope imager [in essence a superpowerful camera] and a device called a coronograph, which blocks out the light of that planet's star.
Brogi's team has proposed a combination of the two techniques. He suggests using direct imaging to discover the exact location of the planet, and then parsing its light from the light of its star with a high-resolution spectroscope. They will time their analysis with the exoplanet's orbit, as while the planet is approaching Earth it becomes easier for spectroscopes to pick out its light, via the Doppler effect.
Brogi hopes that combining these efforts will allow for a result greater than the sum of its parts, but several obstacles have presented themselves. No existing telescope is sensitive enough to execute this method, although the Giant Magellan Telescope, to be completed in 2021, will be. Even with a more powerful telescope, Brogi also called his hypothesis "based on best case scenarios," with unexpected difficulties likely to present themselves during implementation.
But Brogi remains confident in the ability of his method to examine Earth-like exoplanets and begin in earnest the search for alien life on these planets. The last seven years have been a golden age for the discovery of exoplanets, primarily due to the 2009 launch of NASA's Kepler space observatory, which has identified some 1,300 planets to date.