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

Saturn’s largest moon, Titan, is surprisingly similar to Earth in landscape formations, according to new models produced by planetary scientists.

Seen from space, the moon, larger than the planet Mercury, has other similarities to Earth – including rain-filled rivers, lakes and seas – although on Titan rain is liquid methane , falling through nitrogen winds.

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 in the atmosphere drives the movement of grains on the moon’s surface, allowing clumps of hydrocarbons to come together and form. dunes and plains.

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

Mathieu Lapothe, geologist and lead author of the study, explained that their breakthrough was to identify a process that would allow hydrocarbon-based substances to form grains of sand or bedrock depending on how often the winds blow and the rivers flow,

This allowed them to understand how the distinct dunes, plains and labyrinths of Titan could form.

Titan is the only other body in our solar system, after Earth, that has an Earth-like seasonal liquid transport cycle, and the new model shows how this 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 of these sedimentary environments work together,” said Lposte, assistant professor of geological sciences at Stanford’s School of Earth, Energy & Environmental Sciences.

“If we understand how the different pieces of the puzzle fit together and their mechanisms, we can begin to use the landforms left by these sedimentary processes to say something about Titan’s climate or geologic history and how they might impact on the prospect for life on Titan.’

To build a model capable of simulating the formation of Titan’s distinct landscapes, Laposte and his early colleagues had to solve one of the greatest mysteries concerning sediment on the planetary body: the fragility of organic compounds.

Organic compounds are believed to be much more fragile than inorganic silicate – as found on Earth and Venus – turning to dust rather than wearing away.

On Earth, silicate rocks and minerals on the surface erode into grains of sediment over time, moving through winds and waterways to settle into layers of sediment that eventually become rocks again. .

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

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

Unlike the terrestrial planets, Earth, Mars and Venus, where silicate rocks dominate and produce sediment, on Titan it is solid organic compounds.

So far, scientists have not been able to demonstrate how these compounds turn into grains of sediment that can be transported across the moon’s landscapes and over geologic time.

“As the winds carry the squalls, the squalls collide with each other and with the surface,” Lposte explained.

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

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

Ooids form when calcium carbonate is pulled out of the water column and settles in layers around a grain, like quartz.

What makes ooids unique is their formation by chemical precipitation, which allows the ooids to grow, while the concurrent process of erosion slows growth as the grains are crushed together by waves and rocks. storms.

These two competing mechanisms balance each other out over time to form a constant grain size – a process the researchers believe could also occur on Titan.

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

“We hypothesized that sintering, which involves fusing the grains into a single piece, might counterbalance abrasion as winds carry the grains.”

Armed with a hypothesis about how sediments formed, Lapothet and the study’s co-authors used existing data on Titan’s climate and the direction of wind transport of sediments to explain its distinct parallel bands of geological formations. .

These are dunes near the equator, mid-latitude plains, 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 therefore fine sand grains could be created there – an essential component of dunes.

The study authors predict a lull in mid-latitude sediment transport across the equator, where sintering could dominate and create increasingly coarse grains, eventually becoming bedrock that constitutes the Plains of Titan.

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

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

River flow and rainstorms 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 make up the Labyrinthine Terrains.

“We show that on Titan, just like on Earth and what was the case on Mars, we have an active sedimentary cycle that can explain the latitudinal distribution of landscapes by episodic abrasion and sintering driven by Titan’s seasons,” said Laposte. .

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

The results were published in the journal Geophysical Research Letters.