Scientists have probed the mystery of the missing deltas of Titan

For scientists who want to learn more about the geological history of a planet, the Deltas river is an excellent starting point. The deltas bring together the sediments of a large area in a single place, which can be studied to reveal climatic and tectonic stories or signs of past life. This is why NASA sent its most recent Mars Rover to Jezero Crater, which houses a leading and well -preserved delta.

And that is why planetary scientists are also interested in finding deltas on the Moon Titan of Saturn. Titan is the only planetary body in the solar system in addition to the earth which has liquid which currently crosses its surface, so that its deltas could be a scientific treasure.

A problem: Titan seems to be largely devoid of Deltas, reveals a new study, despite its major rivers of liquid methane and ethane.

“It is a little disappointing as a geomorphologist because Deltas should preserve so much from the history of Titan,” said Sam Birch, deputy professor of the Brown University department, of the environmental and planetary sciences that led work.

But the absence of deltas raises a multitude of new questions.

“We take for granted that if you have rivers and sediments, you get deltas,” said Birch. “But Titan is weird. It’s a playground to study the processes we thought we understood.”

Titan is the largest of 274 confirmed moons in Saturn. Its thick atmosphere of nitrogen and methane gives birth to a multitude of climatic and meteorological characteristics similar to the earth. Titan has clouds, wind and rain as well as rivers, lakes and seas. But instead of water, the Fluid Titan bodies contain methane and ethane, which are liquid at the temperatures of cold surface of Titan.

Scientists learned of Titan’s liquid bodies when Cassini spacecrafts stolen in 2006. Looking at the thick atmosphere of Titan with the synthetic opening radar of Cassini (SAR), the spacecraft revealed spider channels and large flat areas compatible with large liquid bodies.

The SAR images of Cassini, however, were deltas, even in the mouth of the great rivers. However, it was not clear that the deltas were really absent, or if they simply did not appear in the SAR data of Cassini. This is the question that Birch and his colleagues tried to answer with this new study, published in the Journal of Geophysical Research: Planets.

The problem with Cassini’s SAR data is that shallow liquid methane is largely transparent in all images. Thus, even if the SAR images could see the large canals of seas and rivers, it is more difficult to distinguish with confidence the coastal characteristics because it is difficult to see where the coast ends and where the seabed begins.

For the study, Birch has developed a digital model to simulate what the Cassini SAR would see if he looked at a landscaper understands well: the earth. In the model, the water of the rivers and the oceans of the earth was replaced by the methane liquid of Titan, which has different radar absorption properties compared to the water.

“We have mainly made synthetic SAR images of the earth which assume the properties of Titan’s liquid instead of those of the earth,” said Birch. “Once we see SAR images of a landscape that we know very well, we can return to Titan and understand a little better what we are looking at.”

Research revealed that the synthetic SAR images of the Earth clearly resolved the large deltas and many other large coastal landscapes.

“If there are deltas the size of that at the mouth of the Mississippi river, we should be able to see it,” said Birch. “If there are large barriers and similar coastal landscapes like those we see throughout the American Gulf coast, we should be able to see them.”

But when Birch and his colleagues combed Titan images in the light of their new analysis, they came mainly empty. Aside from two probable deltas near the southern pole of Titan, the rest of the rivers of the Moon were entirely without Delta. The researchers found that only about 1.3% of the major Titan rivers that end on the coasts have deltas. On Earth, on the other hand, almost every river similar to a delta.

It is not quite clear why Titan generally lacks deltas, says Birch. The fluid properties of Titan rivers should make them perfectly capable of carrying and depositing sediments. According to the researchers, it may be that sea level on the Titan rises and falls so quickly that the deltas are smeared in the landscape faster than they can be built in one place. Winds and tidal currents along Titan coasts can also play an equally important role in prevention of Delta training.

And missing deltas are not the only mystery raised by new research. The new analysis of Cassini Sar’s data from the Côtes de Titan revealed pits of unknown origin in the depths of lakes and seas. The study also revealed that deep channels on the stages of the seas which seem to have been sculpted by rivers flows, but it is not clear how they arrived.

All these surprises will require more research to fully understand, says Birch.

“This is not what we expected,” said Birch. “But Titan does us a lot. I think that’s what makes it such an engaging place to study.”