Little is known about exoplanets, even less about their atmospheres; however, new research of Titan, Saturn’s largest moon, has led scientists to develop a new understanding of the atmospheres of exoplanets. Although NASA has discovered over 1,000 exoplanets in just the past few decades, all that have been discovered are too far from Earth to observe clearly and accurately. The exoplanet nearest Earth is Alpha Centauri Bb, located in a binary star system that orbits Alpha Centauri B at around 4.3 light years away. Therefore, scientists need an enhanced way to study these mysterious rocky masses.
NASA is now looking to our own solar system for the answer by peering beyond our skies into another world’s sunset. Using a new technique that incorporates orbital velocity and light refraction, scientists at NASA are able to observe the atmosphere of an exoplanet to determine its composition, temperature, structure, and density.
When an exoplanet orbits in front of its host star, a minute amount of the star’s light is filtered through the planet’s atmosphere. Light spectra that comes through telescopes exposes the ways in which that light was altered through the atmosphere before reaching the Earth.
Light from stars, planets, and the sunsets created by the combination can be separated into a spectrum to reveal individual bodies of light, much like prisms do. In the last few years, researchers have been collecting exoplanet atmospheric spectra. Tyler Robinson, a postdoctoral fellow at Ames Research Center, who leads the team pioneering this novel exploration technique, explained that he used Titan has a proxy for this developing research. “It turns out there’s a lot you can learn from looking at a sunset,” he stated.
Robinson, in coordination with NASA, isolated a parallel factor between exoplanet occultations, the transit of a planet across its host star, and sunsets recorded by the Cassini spacecraft’s infrared mapping spectrometer. Using Titan as a template, scientists found that the bluish haze found around the planet was similar to the atmospheric complexes of exoplanets.
They deduced that hazes found high above the normal atmospheric level of planets may restrict what spectra of light it can reveal during transit. Therefore, the observations may only divulge information from an exoplanet’s upper atmosphere. Considering Titan’s upper atmosphere is between 90 and 190 miles above the surface, observations from other exoplanets may distort hypotheses made about its geography and ability to harbor the necessary requirements to support life.
Furthermore, the study found that the hazes above Titan drastically effect light at the shorter wavelengths, the blue end of the spectrum. This is why observations of Titan, made via the Cassini spacecraft, show a blue halo floating above its atmosphere. Previously, models of exoplanets have anticipated that atmospheric haze would influence all parts of the light spectrum. The tests done of Saturn’s largest moon allow these effects to be compared to other exoplanets.
The research team’s new technique applies to nearly all observations taken from orbit around any extrasolar planetary system, as well as the solar system in which we live. Moreover, this means that similar studies can be done on the atmospheres of Mars and Saturn, or any other worlds that have remained nearly undiscovered since the telescope was invented. Although scientists are not able to fully conduct research on exoplanet atmospheres due to their distance from Earth, it seems that much of the research can be done just beyond Saturn’s horizon.
By: Alex Lemieux