There's another world out there where it rains in the summer. It's a world where, like Earth, liquid shapes the landscape, and you can find puddles and ponds and lakes and seas.
This is Titan, Saturn's largest moon. Besides Earth, it's the only other planetary object scientists know of in the solar system with a cycle that forms clouds, rain and surface liquid, says Jason Barnes, an associate professor at the University of Idaho who's been studying Titan for years.
"Titan," Barnes says, "is the coolest place in the solar system."
Now, thanks to research from a team led by Barnes and Rajani Dhingra, one of his students this past year, scientists are understanding more about this world. In January, they published a paper showing evidence of changing seasons and rain on Titan's North Pole, which scientists had previously predicted but were unable to find evidence of. And in June, NASA announced it will let Barnes and a team of scientists to launch a spacecraft to Titan in 2025.
Because it's not just the weather and climate that's so fascinating about Titan.
It's the possibility of life.
Like any scientist studying Titan, Dhingra was drawn to the Earth-like hydrologic process.
But there was something scientists still didn't understand about Titan. They knew there were clouds and rain on southern parts of Titan. And they predicted the same on the North Pole — but there wasn't any evidence of rain on the North Pole yet.
"People were calling it the curious case of missing clouds on the North Pole," says Dhingra, who completed her doctorate from the University of Idaho in the spring of 2019.
So Dhingra studied an image from the spacecraft Cassini taken in 2016. She noticed a brightly reflected region, which didn't show up in other pictures before. When the team led by her and Barnes analyzed it, they determined the brightness was due to the fact that it had recently rained.
It's the "wet sidewalk effect," Barnes says, because it's kind of like pavement just after it rains. When it's wet, you get a reflection from the surface. That's essentially what happened on Titan, and it was a way for the team to prove it rained on the North Pole, something that was challenging to prove due to Titan's thick atmosphere.
It's beneath that thick atmosphere that Barnes hopes to one day uncover secrets about potential life on Titan.
The haze particles of Titan's atmosphere are made up of organic compounds. It's possible that water mixing with the organics can form life — much like life was formed on Earth long ago.
It's not impossible that it's forming life currently, Barnes says.
"We want to send a spacecraft to measure the progression," Barnes says. "When you mix organics and water in an abiotic environment, how close do you get to forming life molecules? Were there molecules that might have been precursors to life on Earth?"
That's why Barnes is excited to send a spacecraft, called Dragonfly, to Titan. NASA funded the project for up to $850 million and it will involve dozens of scientists from around the world led by the Johns Hopkins Applied Physics Laboratory. It would arrive to Titan in 2034.
"That rainfall-based erosion is the most powerful force that governs landscapes on Earth," Barnes says. "And it's one we can't explore anywhere else but Titan."
