Exoplanets: After the Search

Since the first exoplanet was discovered in 1989, our knowledge of what lies beyond our solar system has increased exponentially. We have already found over 700 planets, and even a few that could harbor life as we know it. The question now is, how do we find those life-sustaining worlds? They are light years away, and given that the aliens may not have radio or Twitter to send us a message, how can we know for certain that extraterrestrial life actually exists on them?

The answer comes from light. Different chemicals absorb the photons in light at different parts of the spectrum, and can be used as a fingerprint. If we image the planet, we can run the light given off from it through a machine called a spectrograph, which analyzes the data to determine the chemicals in the planet’s atmosphere. Some chemicals, which scientists call biomarkers, may hint at life on the planet. They include gasses like oxygen and methane, which are constantly produced by the respiration process of plants and bacteria. Scientists also look for a reddish tint, called the “red edge,” that can point to vegetation on a planet. None of the data is foolproof however, and the likelihood that it might be created by something nonliving must also be considered. Scientists have been trying to map out what Earth’s atmosphere and spectrum absorption looked like at different stages of its history to serve as a baseline for comparison.

So how do we know these far-flung planets exist at all? We see them only indirectly, based on when they eclipse or distort the gravity of their star. The light from their suns or the bigger planets in their vicinity would usually overshadow a clear image. Scientists are using a technique called adaptive optics to get past this problem. This includes blocking out the outer ring of the star’s light when you view the planet, increasing the viewing angle of the telescope, or manipulating the light to get rid of noise.

Alternatively, we can also tell what’s on a planet through its brightness, even if the image is unclear. The percentage of light that bounces off a surface of a planet differs depending on its material. For example, sand reflects differently than gas, water, forests, and even rock. Comparing the observed reflected light to a theoretical model can let us glimpse at the planet’s ground level.

Yet, despite all this uncertainty, planet hunters may stumble upon an alien ecosphere sooner that we think.

Find out more about these breathtaking discoveries at Exoplanets: The Search for New Worlds on Saturday, June 2nd, where guest scientists, including Sara Seager, a pioneer in exoplanet-atmosphere detection, will discuss this bold new frontier.