Sunsets on Saturn's moon Titan help understand hazy atmosphere of exoplanets

Scientists working with data from NASA's Cassini mission have used Saturn's smog-enshrouded moon Titan as a stand-in to develop a new way to understand the atmospheres of exoplanets.

The new technique shows the dramatic influence that hazy skies could have on our ability to learn about these alien worlds orbiting distant stars.

The work was performed by a team of researchers led by Tyler Robinson, a NASA Postdoctoral Research Fellow at NASA's Ames Research Center in Moffett Field, California.

"It turns out there's a lot you can learn from looking at a sunset," Robinson said.

Light from sunsets, stars and planets can be separated into its component colors to create spectra, as prisms do with sunlight, in order to obtain hidden information.

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 are a record of that imprint.

Spectra enable scientists to tease out details about what exoplanets are like, such as aspects of the temperature, composition and structure of their atmospheres.

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

In the process, Titan's sunsets revealed just how dramatic the effects of hazes can be.

The findings were published May 26 in the Proceedings of the National Academy of Sciences.