Tag: Saturn

A new theory proposes that some of the smaller high rimmed methane lakes on Titan were formed when underground nitrogen warmed and exploded, forming the basin in which the methane ponded.

Most existing models that lay out the origin of Titan’s lakes show liquid methane dissolving the moon’s bedrock of ice and solid organic compounds, carving reservoirs that fill with the liquid. This may be the origin of a type of lake on Titan that has sharp boundaries. On Earth, bodies of water that formed similarly, by dissolving surrounding limestone, are known as karstic lakes.

The new, alternative models for some of the smaller lakes (tens of miles across) turns that theory upside down: It proposes pockets of liquid nitrogen in Titan’s crust warmed, turning into explosive gas that blew out craters, which then filled with liquid methane. The new theory explains why some of the smaller lakes near Titan’s north pole, like Winnipeg Lacus, appear in radar imaging to have very steep rims that tower above sea level – rims difficult to explain with the karstic model.

This is a theory that has merit. It also must be treated with skepticism, as our knowledge of Titan remains at this time very superficial, even with the more detailed information garnered from Cassini.

Based on data from Cassini’s last fly-by of Titan, scientists have been able to estimate the depth of some of that planet’s northern lakes while also finding that they were filled mostly with methane.

The depths measured were as much as 300 feet. The data also shows that the geology of one hemisphere in the north was different from the other hemisphere.

On the eastern side of Titan, there are big seas with low elevation, canyons and islands. On the western side: small lakes. And the new measurements show the lakes perched atop big hills and plateaus. The new radar measurements confirm earlier findings that the lakes are far above sea level, but they conjure a new image of landforms – like mesas or buttes – sticking hundreds of feet above the surrounding landscape, with deep liquid lakes on top.

The fact that these western lakes are small – just tens of miles across – but very deep also tells scientists something new about their geology: It’s the best evidence yet that they likely formed when the surrounding bedrock of ice and solid organics chemically dissolved and collapsed. On Earth, similar water lakes are known as karstic lakes. Occurring in in areas like Germany, Croatia and the United States, they form when water dissolves limestone bedrock.

This data also suggests, as has previous data, that Titan could very well have extensive underground cave systems. Unlike the Moon or Mars, however, these are not going to be very hospitable to colonization, considering the presence of methane and the cold temperatures.

The uncertainty of science: In a review of Cassini data from 2016, scientists have finally identified rain in the northern polar regions of Titan, signaling the onset of summer there.

The whole Titan community has been looking forward to seeing clouds and rains on Titan’s north pole, indicating the start of the northern summer, but despite what the climate models had predicted, we weren’t even seeing any clouds,” said Rajani Dhingra, a doctoral student in physics at the University of Idaho in Moscow, and lead author of the new study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union. “People called it the curious case of missing clouds.”

Dhingra and her colleagues identified a reflective feature near Titan’s north pole on an image taken June 7, 2016, by Cassini’s near-infrared instrument, the Visual and Infrared Mapping Spectrometer. The reflective feature covered approximately 46,332 square miles, roughly half the size of the Great Lakes, and did not appear on images from previous and subsequent Cassini passes.

Analyses of the short-term reflective feature suggested it likely resulted from sunlight reflecting off a wet surface. The study attributes the reflection to a methane rainfall event, followed by a probable period of evaporation. “It’s like looking at a sunlit wet sidewalk,” Dhingra said.

Though the data somewhat matches their climate models, those models did not predict the rain’s late arrival, which means they need revision. I guarantee that this will not be the last revision, though without an orbiter at Saturn it will probably be decades before we have new data to make that possible.

The Cassini science team today released a mosaic of the last images Cassini took of Titan before it crashed into Saturn’s atmosphere four days layer.

The mosaic shows Titan’s north polar region, and shows seas, lakes, and spotty clouds. The lack of clouds is a puzzle to scientists, as they had expected the north polar region to be cloud-covered at this time as summer arrived there, as had been seen at the south pole.

During Titan’s southern summer, Cassini observed cloud activity over the south pole.

However, typical of observations taken during northern spring and summer, the view here reveals only a few small clouds. They appear as bright features just below the center of the mosaic, including a few above Ligeia Mare. “We expected more symmetry between the southern and northern summer,” said Elizabeth (“Zibi”) Turtle of the Johns Hopkins Applied Physics Lab and the Cassini Imaging Science Subsystem (ISS) team that captured the image. “In fact, atmospheric models predicted summer clouds over the northern latitudes several years ago. So, the fact that they still hadn’t appeared before the end of the mission is telling us something interesting about Titan’s methane cycle and weather.”

The truth is we haven’t the slightest idea whether the clouds over the south pole during its previous summer were normal or an aberration. We have barely seen a full year of seasons at Saturn and Titan. To confidently extrapolate any pattern from this slim data is silly.