Sunsets on Titan Reveal Complexity of Hazy Exoplanets

Scientists have developed a new way of studying the atmospheres of exoplanets by using Saturn's smog-enshrouded moon, Titan. The new technique shows the significance hazy skies could have on our ability to learn about these alien worlds orbiting distant stars.

A team of researchers working with data from NASA's Cassini mission found that despite the vast distances between Earth and far away planets, their new technique sheds light on the spectra of exoplanets.

"It turns out there's a lot you can learn from looking at a sunset," lead author Tyler Robinson said in a NASA news release.

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. As an exoplanet 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, experiencing subtle but measureable changes. This process imprints information about the planet that can be collected by telescopes.

Understanding spectra are important because they enable scientists to ascertain details about exoplanets, such as aspects of the temperature, composition and structure of their atmospheres.

Since studying planets outside of our solar system poses a challenge, scientists simply observed Saturn's Titan star, whose sunset mimics the transits of exoplanets. They expect that like Titan, exoplanets are obscured by haze and clouds that present a major obstacle for understanding transit observations.

Cassini's visual and infrared mapping spectrometer instrument revealed that hazes limit transit observers from seeing the entire spectra. Using Titan as a reference, that means you could only view spectra about 90 to 190 miles (150 to 300 kilometers) above its surface.

In addition, Titan's hazes more strongly affect shorter wavelengths, or bluer, colors of light. Previous studies had wrongly assumed that hazes equally affected all colors of the spectra.

"It's rewarding to see that Cassini's study of the solar system is helping us to better understand other solar systems as well," said Curt Niebur, Cassini program scientist at NASA Headquarters in Washington.