Titan’s Massive Dunes May Be a Comet and Moon Graveyard From the Early Solar System

A new modeling study suggests the dark dunes on Saturn’s largest moon are made of tiny particles created by crashing comets and moonlets billions of years ago

An image of Titan taken by the Cassini rover, which shows the darker dunes on the moon's equatorial surface.
The darker areas across Titan's equatorial regions represent its dunes, as taken by the Cassini rover. NASA / JPL / UNIVERSITY OF ARIZONA / UNIVERSITY OF IDAHO

Saturn’s largest moon Titan has an enigmatic air fit for a Dune script. Covered in dark, ridged dunes and craters, the world is wrapped in a golden atmosphere and thought to contain a liquid ocean beneath its icy surface. Its distinct polar and desert regions have intrigued and mystified astronomers for years.

Now, in research presented at the Lunar and Planetary Science Conference this month, scientists suggest a new creation story for Titan’s characteristic ridges. These dark dunes might be a graveyard of fragments from crashed comets and small moons that collided with Titan as the solar system formed.

Titan’s dunes comprise about six million square miles of the moon, but astronomers have long questioned where they came from. Many had thought the sun’s radiation causes tiny particles to fall from the moon’s hazy atmosphere and collect on its surface, where they pile into grainy dunes. But researchers never knew for sure how these microscopic particles enlarged into sand-sized particulates, or whether the atmospheric fragments would have even stayed intact as the dunes took shape.

A shadowy orange sand dune in the United Arab Emirates' Arabian Desert
The Arabian Desert, where sand dunes are approximately the same size as Titan's. Mlenny via Getty Images

Instead, William Bottke, a planetary scientist at the Southwest Research Institute, and his team have proposed an alternative story that taps into various popular theories for how our solar system formed. Some four billion years ago, movements of the giant planets may have destabilized the Kuiper belt—a ring of icy space objects beyond the current orbit of Neptune—leading to an era of frequent collisions.

These planets are surrounded by moons, and this chaotic reshuffling would have caused countless comets and irregular moonlets to smash into Titan and other early planetary bodies. Space rocks would have also crashed together, breaking down into tiny particles. Bottke and his team ran simulations of this era and found that more than enough dust and particulates would have been released and scattered to form Titan’s dunes.

“Irregular satellites collisionally grind really effectively,” says Bottke to New Scientist’s Leah Crane. “Titan gets on the order of about 106 kilometers cubed of material, and that’s several times more than the dunes.”

Per the team’s models, a similar amount of material would have been delivered to Jupiter’s moons Callisto and Ganymede, which might explain why they also have regions coated in dark particles today.

Because many of these smashed-comet particles have passed through Earth’s atmosphere, scientists know a lot about them—including that their size, durability and color are in line with what we know about Titan’s dunes, Bottke says to Science News’ Nikk Ogasa.

Titan, Saturn's largest moon, passes in front of Saturn
Titan, which NASA plans to study with a lander in 2034, passes in front of Saturn. NASA / JPL-CALTECH / SPACE SCIENCE INSTITUTE

Still, the hypothesis isn’t a slam dunk. Jani Radebaugh, a planetary scientist at Brigham Young University who was not involved in the research, tells Science News that Titan’s volcanic activity may “create a problem” for this theory, since debris from eruptions would have buried these scattered particles over time.

Radebaugh also presented research at the conference, using computer models to hypothesize that Titan’s geology may be slightly more asymmetrical than previously thought. Sand dunes likely dominate Titan’s lower latitudes, but yardangs—long, straight ridges formed by erosion—may stretch across the moon’s upper latitudes, her study suggests. This imbalance could indicate different weather conditions on different parts of the moon.

“On Titan, maybe there just isn’t sand at the high latitudes, or maybe there is material there that is more easily eroded,” Radebaugh tells New Scientist’s Leah Crane.

Computer modeling studies like these can help scientists visualize dynamics on a world we can’t easily reach, but direct observations of the moon are on the horizon. Soon, an upcoming mission from NASA should be able to provide answers to Bottke and Radebaugh’s questions.

Announced in 2019, NASA’s Dragonfly mission is preparing for a 2028 launch to Titan, where a lander will study varied locations, searching for chemical evidence of life and clues into the world’s environmental history. Titan’s liquid reservoirs, subsurface ocean, thick atmosphere and dune fields will be explored like never before.

“Titan is unlike any other place in the solar system, and Dragonfly is like no other mission,” Thomas Zurbuchen, formerly NASA’s associate administrator for science, said in a 2019 statement announcing the mission. “Dragonfly will visit a world filled with a wide variety of organic compounds, which are the building blocks of life and could teach us about the origin of life itself.”

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