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Titan’s Sunsets Give Insight To Hazy Atmospheres of Exoplanets

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Lisa Winter

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1045 Titan’s Sunsets Give Insight To Hazy Atmospheres of Exoplanets
Artist's rendering of NASA's Cassini spacecraft observing a sunset through Titan's hazy atmosphere. Image credit: NASA/JPL-Caltech

Certain characteristics of exoplanets can be difficult to study due to their atmospheres obscuring details. NASA scientists have begun to Saturn’s moon Titan at sunset, in the hope that it will help them to understand the haze from the atmosphere and what it could reveal about surface conditions. The study was led by Tyler Robinson of NASA's Ames Research Center and the paper was published in the Proceedings of the National Academy of Sciences.

An atmosphere can act like a prism, separating light that passes through it into a spectrum of its components. The result of this spectrum provides information about the planetary body’s atmospheric composition, temperature, and structure, giving clues about its habitability. For exoplanets, this information is obtained as it transits its parent star. The light that goes through the atmosphere isn’t much different, but different enough to obtain meaningful information.


Titan’s atmosphere produces a haze just like an exoplanet, and it is strongest at sunset. The Cassini orbiter, which has been studying Saturn up close since 2004, has also gathered a considerable amount of information about Titan. By comparing information about Titan from when it produces the heaviest amount of haze versus when the haze is not as strong, scientists will be able to clarify findings and refine techniques used on exoplanets.

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

The heavy haze created by Titan, and presumably many exoplanets as well, may overcomplicate some of the spectral information collected by researchers. However, many models currently used by astronomers tend to err on the side of being overly simplified due to constraints of computing power. For this study, the researchers analyzed four instances of Titan’s haze, using Cassini’s visual and infrared mapping spectrometer instrument. 

They found that the haze makes it very difficult to collect information about anything beyond the uppermost layer of the atmosphere. Titan’s lack of gravity (when compared to Earth) allows its atmosphere to extend out about 600 km (370 miles) around it. However, the haze only allows instruments to detect the upper 150-300 km (90-190 miles). This prohibits scientists from gathering information about the lower parts of the atmosphere, which is more dense and has complex attributes.


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

The team also found that the haze was more likely to block out blue light, which has a shorter wavelength. This could have considerable implications for previous analyses of exoplanets, as current models are based on the assumption that all wavelengths in the visible spectrum would be equally affected. 

The technique used on Titan could also be applied to Mars and Saturn. Using the information gathered from within our own solar system in the search for exoplanets greatly extends the usefulness of the orbiters and will allow scientists to gather more information about other worlds in the Universe.


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