Despite the staggering distances to other planetary systems, in recent years researchers have begun to develop techniques for collecting spectra of exoplanets.

When one of these worlds transits, or passes in front of its host star as seen from Earth, some of the star’s light travels through the exoplanet’s atmosphere, where it is changed in subtle, but measurable, ways.

This process imprints information about the planet that can be collected by telescopes. The resulting spectra enable scientists to tease out details about the temperature, composition and structure of exoplanets’ atmospheres.

Robinson and his colleagues exploited a similarity between exoplanet transits and sunsets witnessed by the Cassini spacecraft at Titan. Called solar occultations, these observations allowed the scientists to observe Titan as a transiting exoplanet without having to leave the solar system.

Many worlds in our solar system, including Titan, are blanketed by clouds and high-altitude hazes. Scientists expect that many exoplanets would be similarly obscured.

Clouds and hazes create a variety of complicated effects that must be disentangled from the signature of these alien atmospheres, and present a major obstacle for understanding transit observations. Due to the complexity and computing power required to address hazes, models used to understand exoplanet spectra usually simplify their effects.

“Previously, it was unclear exactly how hazes were affecting observations of transiting exoplanets,” said Robinson. “So we turned to Titan, a hazy world in our own solar system that has been extensively studied by Cassini.”

Sunsets on Titan are teaching us about distant exoplanets