An artist’s illustration of ancient impact on Saturn’s moon Titan
Science Photo Library / Alamy Stock Photo
By Jonathan O’Callaghan
Saturn’s icy moon Titan has long interested scientists in the search for life in the solar system. Its surface is covered with organic hydrocarbons, and the icy crust is suspected to cover an aqueous ocean. According to a new study, an asteroid or comet hitting the moon could theoretically mix these two ingredients, with the resulting impact craters being an ideal place to get started.
The idea is ‘very exciting’, says 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 hot pool on the surface, then you could have living conditions,” she says. And, “If you let organic matter cycle from the surface into the ocean, it makes the ocean a little more habitable.”
Scientists have believed that an ocean has been sitting about 100 kilometers below Titan’s crust since 2012, when NASA’s Cassini mission measured sight variations in the moon’s tides. Alvaro Penteado Crósta, a planetary geologist at the University of Campinas, knew that the moon was full of large impact craters. He asked himself if any of the collisions were large enough to pierce the crust and stir up the organic matter of the surface with the water beneath it. It may have produced a primordial soup that you would need to develop life, ‘says Penteado Crósta.
To find out, he and his colleagues modeled the impact of the moon’s largest crater, the 425-kilometer Menrva, which is thought to have formed 1 billion years ago. The model suggested that the crater was the result of a 34-kilometer-wide space rock hitting the surface at 7 kilometers per second.
The impact that Menrva, Titan’s largest crater, has made has possibly stung the icy crust of the moon.
NASA
The heat of the impact would, according to the model, have created a lake in the crater, which the team presented at the Lunar and Planetary Science Conference this week. The lake would probably have existed only 1 million years before it froze in the icy temperature of Titan. However, Penteado Crósta says it has had enough time for microbes to develop, with the benefit of liquid water, organic molecules and heat. “It’s pretty good for bacteria.”
Although the team’s research focused on Menrva, Penteado Crósta says it is possible that smaller collisions were sufficient to break through Titan’s ice shell, perhaps even at Selk – a 90-kilometer-wide crater about 5,000 kilometers away. It is believed that Selk is much younger than Menrva, perhaps only a few hundred million years old, which means that any evidence of life there will be fresh. “Selk is more likely to preserve some kind of fossilized bacteria in the ice,” says Penteado Crósta.
Selk is the planned landing site for NASA’s Dragonfly mission, a $ 1 billion autonomous and nuclear-powered drone that will be launched in 2027 and arrive on Titan 2036. If the impact breaks the ice crust here, the mission can figure it out.
But Elizabeth Turtle, lead researcher for the Dragonfly mission at the Johns Hopkins University Applied Physics Laboratory, is not so sure that it did happen. “There is no strong evidence that you pierced,” she says.
Yet Dragonfly can visit other craters in an extended mission. And while Menrva may be too far away, it could be an interesting landing site in the future, says Penteado Crósta.