Nasa's Cassini: Sunsets on Saturn's Moon Titan Explains Atmospheres of 'Hazy' Alien Worlds

Scientists working on Nasa's Cassini mission have developed a new way of understanding the atmospheres of exoplanets using Saturn's smog-covered moon, Titan.

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

"It turns out there's a lot you can learn from looking at a sunset," said Tyler Robinson, a Nasa postdoctoral research fellow and team leader of the study, as quoted by Headlines & Global News.

Light from sunsets, stars and planets can be separated into its component colours to create spectra, in the same way prisms separate sunlight, in order to obtain hidden information.

Although hazy exoplanets are extremely far away from our planet, researchers have been able to collect their spectra.

When one of these worlds 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 ways. This process imprints information about the planet that can be collected by telescopes. The resulting spectra are a record of that imprint.

Using spectra, scientists are able to work out the characteristics of exoplanets, such as the composition, temperature and structure of their atmospheres.

The team used a similar technique to explore Titan, an exoplanet shrouded by clouds.

"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."

The team used four observations of Titan made between 2006 and 2011 using Cassini's visual and infrared mapping spectrometer instrument, which showed that high hazes could strictly limit what the spectra can reveal about distant worlds.

If an exoplanet is particularly hazy, transit observations may only show researchers details about a planet's upper atmosphere. In the case of Titan, this means between 90 and 190 miles above the surface and high over the bulk of its dense and complex atmosphere.

Titan's hazes also affect shorter wavelengths - the bluer colours - more strongly, although studies of exoplanet spectra have previously assumed that hazes would affect all colours in similar ways.

"People had dreamed up rules for how planets would behave when seen in transit, but Titan didn't get the memo ," said Mark Marley, a co-author of the study, told Forbes. "It looks nothing like some of the previous suggestions, and it's because of the haze."

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

The research was published in the Proceedings of the National Academy of Sciences.