Cassini reveals surprises with Titan's lakes

**Cassini reveals surprises with Titan's lakes
This near-infrared, color view from Cassini shows the sun glinting off of Titan's north polar seas. Credit: NASA/JPL-Caltech/Univ. Arizona/Univ. Idaho

On its final flyby of Saturn's largest moon in 2017, NASA's Cassini spacecraft gathered radar data revealing that the small liquid lakes in Titan's northern hemisphere are surprisingly deep, perched atop hills and filled with methane.

The new findings, published April 15 in Nature Astronomy, are the first confirmation of just how deep some of Titan's lakes are (more than 300 feet, or 100 meters) and of their composition. They provide new information about the way liquid methane rains on, evaporates from and seeps into Titan—the only planetary body in our solar system other than Earth known to have stable liquid on its surface.

Scientists have known that Titan's hydrologic cycle works similarly to Earth's—with one major difference. Instead of water evaporating from seas, forming clouds and rain, Titan does it all with methane and ethane. We tend to think of these hydrocarbons as a gas on Earth, unless they're pressurized in a tank. But Titan is so cold that they behave as liquids, like gasoline at room temperature on our planet.

Scientists have known that the much larger northern seas are filled with methane, but finding the smaller northern lakes filled mostly with methane was a surprise. Previously, Cassini data measured Ontario Lacus, the only major in Titan's southern hemisphere. There they found a roughly equal mix of methane and . Ethane is slightly heavier than , with more carbon and hydrogen atoms in its makeup.

"Every time we make discoveries on Titan, Titan becomes more and more mysterious," said lead author Marco Mastrogiuseppe, Cassini radar scientist at Caltech in Pasadena, California. "But these new measurements help give an answer to a few key questions. We can actually now better understand the of Titan."

Adding to the oddities of Titan, with its Earth-like features carved by exotic materials, is the fact that the hydrology on one side of the northern hemisphere is completely different than the that of other side, said Cassini scientist and co-author Jonathan Lunine of Cornell University in Ithaca, New York.

"It is as if you looked down on the Earth's North Pole and could see that North America had completely different geologic setting for bodies of liquid than Asia does," Lunine said.

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.

Alongside the investigation of deep lakes, a second paper in Nature Astronomy helps unravel more of the mystery of Titan's hydrologic cycle. Researchers used Cassini data to reveal what they call transient lakes. Different sets of observations—from radar and infrared data—seem to show liquid levels significantly changed.

The best explanation is that there was some seasonally driven change in the surface liquids, said lead author Shannon MacKenzie, planetary scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. "One possibility is that these transient features could have been shallower bodies of liquid that over the course of the season evaporated and infiltrated into the subsurface," she said.

These results and the findings from the Nature Astronomy paper on Titan's deep lakes support the idea that hydrocarbon rain feeds the lakes, which then can evaporate back into the atmosphere or drain into the subsurface, leaving reservoirs of liquid stored below.

Cassini, which arrived in the Saturn system in 2004 and ended its mission in 2017 by deliberately plunging into Saturn's atmosphere, mapped more than 620,000 square miles (1.6 million square kilometers) of liquid lakes and seas on Titan's surface. It did the work with the radar instrument, which sent out and collected a return signal (or echo) that provided information about the terrain and the liquid bodies' depth and composition, along with two imaging systems that could penetrate the moon's thick atmospheric haze.

The crucial data for the new research were gathered on Cassini's final close flyby of Titan, on April 22, 2017. It was the mission's last look at the moon's smaller lakes, and the team made the most of it. Collecting echoes from the surfaces of small lakes while Cassini zipped by Titan was a unique challenge.

"This was Cassini's last hurrah at Titan, and it really was a feat," Lunine said


Explore further

Cassini's final view of Titan's northern lakes and seas

More information: Shannon M. MacKenzie et al. The case for seasonal surface changes at Titan's lake district, Nature Astronomy (2019). DOI: 10.1038/s41550-018-0687-6

More information about Cassini can be found here: solarsystem.nasa.gov/cassini

Journal information: Nature Astronomy

Citation: Cassini reveals surprises with Titan's lakes (2019, April 16) retrieved 18 June 2019 from https://phys.org/news/2019-04-cassini-reveals-titan-lakes.html
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Apr 16, 2019
Time for a visit to the surface is looooong overdue !

Apr 16, 2019
I can sympathize with your point of view, HM.

However, Titan is one of the very few, very improbable possibilities of finding Life off Earth.
Compared to the Earth's biosphere?
Titan's biosphere could prove to be unique, truly exotic alien organisms. Perhaps...maybe

I prefer Titan over Mars or any of the ice-covered ocean moons.

It is my opinion that Mars life has been coprolites for billions of years dead.
& that the ocean moons will be found sterile.

This is, I believe the very best reason NOT to rush probes to the surface of Titan.
It would not be useful to contaminate Titan's possibility of a biosphere!
Carelessly contaminating it with Earthlife.

& no, we do not know how to prevent such a catastrophe.

The only real chance would be to follow my StepLadder Infrastructure Plan using orbital automated factories.

Now comes the whining & the tantrums that Stepladder is too conservative & mature a pragmatic method.
All the comicbook readers hate it.

Apr 16, 2019
It would not be useful to contaminate Titan's possibility of a biosphere!


With what? No organism alive on earth can function at Titan's temperatures anyhow because the water in the cells freezes, and all the cells' lipid membranes would be dissolved by the liquid ethane. All the life that we could transport over would freeze and break apart.


Apr 17, 2019
Are the words "hydrology" and "hydrologic cycle" used in the case of Titan due to a lack of a better word, or does the "hydro-" in this case suggest "hydrocarbons" rather than water?

Apr 17, 2019
Good points, Eikka.
But here on Earth we do have exotic organisms that survive if not always thrive in extreme environments, Those maybe the causes of colorful icebergs?

Though I suspect spores might be the greatest danger. Here on Earth, we do not know how to assemble & launch a spacecraft without microscopic stowaways.

It is not bugs on the outside of the rocket that are the danger. But rather, the bugs hiding within the interior of the rocket
Protected from disinfectants & other forms of sterilization.

Shielded from vacuum desiccation
& a full spectrum of radiations.
Especially where over-heating is more damaging then getting temporarily frozen.

That is why StepLadder.
A modestly conservative low cost program of orbital automated factories.
Utilizing space resources.

Manufacturing wth continuous exposure to vacuum & radiation without any exposure to Earth Life.

Ay least we'd be making a "sirius" effort to avoid our doleful history of scewups!

Apr 17, 2019
Are the words "hydrology" and "hydrologic cycle" used in the case of Titan due to a lack of a better word, or does the "hydro-" in this case suggest "hydrocarbons" rather than water?
It's as you suggest, the word hydrology is here being used in a sense of "liquidology", so is being used to describe the actions of liquid rain, lakes, rivers, etc. on Titan as analogues of what liquid water does on Earth.

There's a similar use of the use of the word "geology" when used to describe rocks and sediments on Mars - even though there exists a word "areology" (from Ares = Mars) for that planet. But not many use the "proper" term.

Apr 17, 2019
good question Sahstar. Perhaps you coukd message the researcher's listed for this article & get their opinions?

Maybe see if wiki is accepting "hydro" for Hydrocarbons?
Check around planetary astronomy sites & see if there is any sort of consensus?

Then please post your results back to these comments. Should be interesting answers yo your questions.

Very amusing if there is a lot disagreement among the professionals. That's always good for a chuckle or three!

Apr 17, 2019
But here on Earth we do have exotic organisms that survive if not always thrive in extreme environments, Those maybe the causes of colorful icebergs?


Not at -179 C. The chemistry of DNA doesn't work at all when all the water is frozen. The molecules and materials that form life on earth are mineral-like solids on Titan. Even the hardiest extremophiles would behave more like microscopic beads of sand.

If there is biology on Titan, anything from Earth would appear to it like globs of molten magma looks to us, and behave the same when it cools down to ambient temperature. Imagine a space alien landing on earth, with blood of molten lead and flesh made of red-hot iron.

Apr 17, 2019
@sahstar
Are the words "hydrology" and "hydrologic cycle" used in the case of Titan due to a lack of a better word, or does the "hydro-" in this case suggest "hydrocarbons" rather than water?
as SkyLight indicates, and as the article states, it's about fluid mechanics on the planet
Scientists have known that Titan's hydrologic cycle works similarly to Earth's—with one major difference. Instead of water evaporating from seas, forming clouds and rain, Titan does it all with methane and ethane...
see also: https://en.wikipe...echanics

https://en.wikipe...dynamics

Apr 17, 2019
Eikka, I agree with all your facts & figures. I just cannot support your optimistic viewpoint.

I am not just a pessimist, I am a paranoid cynic.
Belt & suspenders & heavy-duty industrial-grade staples attaching the top of my pants to the bottom of my shirt!

Considering all that may be at stake? Not just for increasing our knowledge of the Universe but also for the survival of an alien biome.

I cannot support any effort that would cut corners just to feed our egos with quick, eventually meaningless exploration.

"Oh look! Another headline extolling our achievements to reach Titan."
"Hooray for our team! "
"Yeah, we did good. Pity about the collapse of the Titan biosphere."
" Well, better luck next time,"
"For sure!"

That is not the road I want to travel.

Apr 19, 2019
. I just cannot support your optimistic viewpoint.


The only counterpoint I could see is that we would introduce organic chemicals to Titan that they already don't have, and those could then act as part of another type of life unlike ours and foreign to Titan as well. I.e. we could start a shadow biosphere that would compete as an invader.

However, the same chemistry is already working there. The building blocks of DNA came to earth on asteroids and can be found in space - there's nothing we can add that they already don't have. If anything, the chemicals we would bring along would be food to life that already exists there. Alternatively, it turns out to be poisons, but the effect would be limited to the immediate surroundings.

In a very very unlikely event, we could introduce something akin to a virus, but that's effectively a snowball's chance in hell considering how different life would be on Titan to function at all.

Apr 19, 2019
You can imagine it the other way around: take a planet like Venus where everything is +200 C or above on the surface.

Suppose a lifeform from Venus came to earth. If they could survive here, if it was possible at all, we would already have extremophiles that operate at temperatures of molten lead.

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