Seven hundred leagues under Titan’s methane seas

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What could be more exciting than flying a helicopter over the deserts of Mars? How about playing Captain Nemo on Saturn’s big misty moon Titan – probe the depths of a methane ocean, dodge hydrocarbon icebergs, and explore an ancient icy shore of organic goo a billion miles from the sun ?

These are the visions that have crossed my mind recently. The eyes of humanity are on Mars these days. A convoy of robots, after half a year in space, fell, one after another, in orbit or directly to the ground on the red planet, like jets entering JFK Among the cargo is a helicopter as armchair astronauts eagerly await flying over the Martian sands.

But my own attention was diverted to the more remote parts of the solar system by the news that Kraken Mare, an ocean of methane on Titan, had recently been measured for its depth and had probably descended to at least 1,000 feet. It’s as deep as nuclear submarines will admit to going. The news rekindled my dreams of what I think is the most romantic of space missions: a journey over, and ultimately even beneath, the oceans of Titan.

“The depth and composition of each of Titan’s seas had already been measured, with the exception of Titan’s largest sea, Kraken Mare – which not only has a big name, but also contains around 80% of surface liquids. of the moon, ”said Valerio Poggiali, research associate at the Cornell Center for Astrophysics and Planetary Science. Dr Poggiali is the lead author of an article describing the new depth measurements in the Journal of the American Geophysical Union.

NASA recently announced that it will launch a drone called Dragonfly on the Saturnian moon in 2026. Proposals have also been circulating for an orbiter, a floating probe that could splash in a lake, or even a robotic submarine.

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“The Titan submarine is still running,” Dr Poggiali said in an email, although that probably won’t happen until Titan next summer, around 2047. By then, he says , there will be more ambient light and the submarine could eventually communicate on a direct line to Earth without the need for a radio relay in orbit.

Titan is the strangest place in the solar system, in some ways, and also the world most like ours. Like Earth, it has a thick atmosphere composed mostly of nitrogen (the only moon that has much of an atmosphere), and like Earth, it has weather, rain, rivers, and seas.

But on this world, when it rains, it rains gasoline. Hydrocarbons drift like snow and are shaped into dunes by nitrogen winds. Rivers have carved canyons through mountains of frozen soot, and layers of ice float over the underground ammonia oceans. The prevailing surface temperature is minus 290 degrees Fahrenheit. A chemical sludge that optimistic astronomers call “prebiotic” crawls under an oppressive brown sky. Besides Earth, Titan is the only world in the universe known to harbor liquid on its surface – with all that that might entail.

Astrobiologists have been eager to take a closer look at this world since Voyager passed it in 1980 and radioed evidence that its smoggy atmosphere was four times as dense as ours. Time, technology and human ingenuity have since revealed that this cloudy world is a natural wonderland.

The northern regions of Titan are bordered by a network of lakes and rivers. The largest of these, called Kraken Mare, named after a Nordic monster, is larger than all of the Great Lakes of North America combined.

The Cassini orbiter spent 13 years buzzing through the Saturnian system, mapping these features in detail.

On August 21, 2014, when Cassini passed about 600 miles over the northern kingdoms of Titan, he used his radar altimeter to measure depths at Kraken Mare and Moray Sinus, an estuary on the northern sea coast. Engineers could measure the depths of the seas by noting the delay between when the radar bounced off the surface and when it bounced off the seabed.

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Moray Sinus turned out to be about 280 feet deep, but there was no returning echo from the Kraken bottom; either the lake was very, very deep or it was absorbing the radar signals so completely that they never escaped.

“So the central part of Kraken Mare must be deeper than 330 feet and probably more than 1000 feet,” concluded Dr Poggiali.

Another major surprise, he said, was the composition of Kraken Mare. Scientists expected it to contain relatively more ethane, which is denser than methane, than Titan’s northernmost sea, Ligeia Mare.

According to Dr. Poggiali, in the dominant models of hydrology of Titan, the presence of methane-nitrogen rain increases with increasing latitude. This would make the composition of the more “pole” seas richer in methane. “Simply put, ethane behaves a lot like salt in seawater on Earth,” he said.

He added: “Of course the composition we got for the liquid filling the Moray Sinus, that big bay in the northern part of Kraken Mare, is quite surprising. We expected it to be significantly richer in ethane. What we found, instead, is that the Kraken is much more similar to the Ligeia Mare, Titan’s second largest sea. This has important implications for the functioning of the hydrological cycle. There could still be more ethane in the southern parts of the Kraken Mare, he added, but the existing data does not go that far.

This is more than an abstract planetary science. In the imagination of scientists like Dr Poggiali, Titan is a laboratory where, for millions of years, chemistry could have been taught to generate energy and store information. “These are processes that have happened on our planet too, but they haven’t left any traces! As you can probably see, we need to get back to Titan to better understand the mystery of life. he said.

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Like an old captain sitting on the dock, Dr Poggiali started the possible voyages of a 20-foot-long NASA submarine. The trip would start in the center of Kraken Mare and move up to Moray Sinus, where the submarine would spend three weeks measuring tides and settlements before sailing the coasts, crossing the Bayta Fretum Strait and heading for the south through a gorge-shaped passage called Seldon Fretum.

During these explorations, the ship would periodically map and sample the seabed and collect detailed images of the shore where possible. Titan’s surface gravity is lower than that of Earth, so a small submarine could venture deeper without being crushed by pressure like it would in a terrestrial ocean of saltwater.

Additionally, Dr Poggiali said, because methane is transparent to radio waves, the submarine may be able to transmit data directly to Earth while it is still submerged. In total, over 90 days, the small submarine could travel 2,000 miles under the sea, at a speed of one foot per second, according to a NASA website describing the proposed submarine.

Meanwhile, I can hardly be faulted for still dreaming of Titanic giant squid frolicking around in this freezer-filled cosmic natural gas aquarium.

Since the beginnings of the space program, cosmic visionaries have described space as a “new sea,” as President John F. Kennedy said in a speech at Rice University in 1962. He never did. dreamed that we could actually navigate below.