An artist’s illustration of ancient impacts on Saturn’s moon Titan
Science Photo Library / Alamy Stock Photo
By Jonathan O’Callaghan
Saturn’s frigid moon Titan has long intrigued scientists looking for life in the solar system. Its surface is covered with organic hydrocarbons, and the ice crust is believed to cover a watery ocean. An asteroid or comet hitting the moon could theoretically mix these two ingredients, according to a new study, with the resulting impact craters providing an ideal place to start life.
The idea is “very exciting,” said Léa Bonnefoy, a planetary scientist and Titan expert at the University of Paris. “If you have a lot of liquid water that creates a temporary warm pool on the surface, then you can have conditions that are favorable for life,” she says. And: “If you let organic material cycle from the surface into the ocean, it makes the ocean a bit more habitable.”
Scientists have believed that an ocean is about 100 kilometers below Titan’s crust since 2012, when NASA’s Cassini mission measured the variations in visibility in the moon’s tides. Alvaro Penteado Crósta, a planetary geologist at the University of Campinas, knew the moon was pockmarked with many large impact craters. He wondered if any of the impacts were big enough to pierce the crust and churn the organic matter off the surface with the water underneath. That may have provided “a primordial soup you need to develop your life,” says Penteado Crósta.
To find out, he and his colleagues modeled the impact for the moon’s largest crater, 425 kilometers wide Menrva, which was believed to have formed 1 billion years ago. The model suggested that the crater was the result of a 21 miles wide space rock hitting the surface at a speed of 7 kilometers per second.
The impact made by Menrva, Titan’s largest crater, may have punctured the moon’s icy crust.
NASA
The heat of the impact would have created a lake in the crater, according to the model the team presented at this week’s Lunar and Planetary Science Conference. The lake would likely only have existed for 1 million years before freezing in Titan’s icy temperatures. But Penteado Crósta says this may have been enough time for microbes to evolve, using liquid water, organic molecules and heat from the impact. “That’s pretty good for bacteria.”
Although the team’s research focused on Menrva, Penteado Crósta says it is possible that smaller impacts were enough to break through Titan’s ice cover, perhaps even at Selk – a 90-kilometer-wide crater about 3,000 kilometers away. Selk is believed to be much younger than Menrva, perhaps only a few hundred million years old, which would mean any evidence of life would be fresher there. “Selk may be more likely to keep some fossilized bacteria in the ice,” said Penteado Crósta.
Selk is the planned landing site for NASA’s Dragonfly mission, a $ 1 billion autonomous and nuclear-powered drone that will launch in 2027 and arrive at Titan 2036. If the impact here broke the ice crust, the mission could find out.
But Elizabeth Turtle, principal investigator on the Dragonfly mission at Johns Hopkins University Applied Physics Laboratory, isn’t so sure. “There is no strong evidence to suggest that you actually had a flat tire,” she says.
Still, Dragonfly was able to visit other craters on an extended mission. And while Menrva may be too far away, it could become an intriguing landing spot in the future, says Penteado Crósta.