Scientists model the surface of Titan, Saturn’s largest moon

Saturn’s largest moon, Titan, is strikingly Earth-like when it comes to landscape features, according to new models produced by planetary scientists.

When viewed from space, the moon, larger than the planet Mercury, has other similarities to Earth, including rain-filled rivers, lakes, and seas, although on Titan the rain is liquid methane, which falls via winds of nitrogen.

These materials produce hydrocarbon sand dunes that are very different from silicate sedimentary structures elsewhere in the solar system, according to a team of planetary scientists from Stanford University in California.

The formation of the sand dunes, near rivers, lakes and oceans filled with liquid methane, was enigmatic and difficult to pin down, the team explained.

They created a series of computer models that revealed that an Earth-like seasonal cycle within the atmosphere drives the movement of grains on the moon’s surface, allowing hydrocarbon clumps to coalesce and form the dunes and plains.

Titan is viewed by many scientists as a prime candidate for future human colonization, due to its relative habitability, including seasonal cycle and climate system.

Mathieu Lapôtre, a geologist and lead author of the study, explained that his breakthrough was the identification of a process that would allow hydrocarbon-based substances to form grains of sand or bedrock, depending on how often the winds blow and the flows flow. streams.

This allowed them to understand how Titan’s various dunes, plains, and labyrinthine terrains might form.

Titan is the only other body in our solar system, after Earth, that has a similar seasonal cycle of liquid transport to Earth, and the new model shows how that seasonal cycle drives the movement of grains on the moon’s surface. .

“Our model adds a unifying framework that allows us to understand how all these sedimentary environments work together,” said Lapôtre, an assistant professor of geological sciences in the Stanford School of Earth, Energy and Environmental Sciences.

“If we understand how the different pieces of the puzzle and their mechanics fit together, then we can start to use the landforms left behind by those sedimentary processes to say something about Titan’s climate or geological history, and how they might affect perspective.” for life on Titan.

To build a model that could simulate the formation of Titan’s distinct landscapes, Lapôtre and his colleagues first had to solve one of the biggest mysteries about sediments in the planetary body: the fragility of organic compounds.

Organic compounds are thought to be much more brittle than inorganic silicates, such as those found on Earth and Venus, and turn to dust rather than wear away.

On Earth, silicate rocks and minerals on the surface erode into sediment grains over time, moving through winds and currents to settle into layers of sediment that eventually revert back to rock.

Those rocks then continue through the erosion process and the materials are recycled through the Earth’s layers over geologic time.

On Titan, researchers believe similar processes formed the dunes, plains, and labyrinthine terrain seen from space.

Unlike the terrestrial planets Earth, Mars, and Venus, where silicate rocks dominate and produce sediments, on Titan these are solid organic compounds.

Scientists have so far been unable to show how these compounds break down into sediment grains that can be transported across the moon’s landscapes and over geologic time.

“As grains are carried by winds, the grains collide with each other and with the surface,” Lapôtre explained.

‘These collisions tend to decrease grain size over time. What we were missing was the growth mechanism that could counteract that and allow the sand grains to maintain a stable size over time,” he said.

They found a solution by looking at a special type of sediment found in Earth’s shallow tropical seas, known as ooids, which are small spherical grains.

Ooids form when calcium carbonate is extracted from the water column and adheres in layers around a grain, such as quartz.

What makes ooids unique is their formation through chemical precipitation, which allows them to grow, while the simultaneous process of erosion slows growth as waves and storms crush the grains together.

These two competing mechanisms balance each other out over time to form a constant grain size, a process the researchers suggest could also be occurring on Titan.

“We were able to solve the paradox of why there could be sand dunes on Titan for so long even though the materials are very weak,” Lapôtre said.

“We hypothesized that sintering, which involves neighboring grains fusing together into one piece, could counteract abrasion when grains are carried by winds.”

Armed with a hypothesis for sediment formation, Lapôtre and study co-authors used existing data on Titan’s climate and the direction of wind-driven sediment transport to explain its distinct parallel bands of geological formations.

That is, dunes near the equator, plains in the mid-latitudes, and labyrinthine terrain near the poles.

Atmospheric modeling and data from the Cassini mission reveal that winds are common near the equator, supporting the idea that less sintering and thus fine sand grains, a critical component of dunes, could be created there. .

The study authors predict a pause in sediment transport in mid-latitudes on both sides of the equator, where sintering could dominate and create increasingly coarse grains, eventually becoming the bedrock that makes up Titan’s plains.

Sand grains are also necessary for the formation of the moon’s labyrinthine terrain near the poles.

The researchers think these distinct ridges might be like karsts in limestone on Earth, but on Titan, they would be collapsed features made of dissolved organic sandstones.

River flow and rain storms occur much more frequently near the poles, making sediment more likely to be transported by rivers than by winds.

A similar process of sintering and abrasion during river transport could provide a local supply of coarse sand grains, the source of the sandstones thought to form labyrinthine terrains.

“We are showing that on Titan, just like on Earth and what used to be the case on Mars, we have an active sedimentary cycle that can explain the latitudinal distribution of landscapes through episodic abrasion and seasonally driven sintering.” of Titan,” Lapôtre said. .

“It’s quite fascinating to think about how this alternate world exists so far away, where things are so different and yet so similar.”

The findings have been published in the journal Geophysical Investigation Letters.