Seven Hundred Leagues Beneath Titan’s Methane Seas
What could be more exciting than flying over the deserts of Mars in a helicopter? How about playing Captain Nemo on Saturn’s tall, misty moon Titan – plumbing the depths of a methane ocean, dodging hydrocarbon icebergs, and exploring an old, cold coast of organic pulp that is a billion miles from the Sun?
These are the visions that have been dancing through my head lately. The eyes of mankind are on Mars these days. After half a year in space, a convoy of robots fell one after the other into orbit or directly to the bottom of the Red Planet, like jets arriving at JFK. Under the cargo is a helicopter, on which chair astronauts can happily fly over the sand of Mars.
But my own attention was drawn to the wider solar system by the news that Kraken Mare, a methano ocean on Titan, had recently been measured for depth and probably sunk at least 300 meters. That as deep as nuclear submarines will admit to going. The news sparked my dreams of what I consider to be the most romantic space mission: a trip to and ultimately even under the oceans of Titan.
“The depth and composition of each of the Titan’s seas has already been measured, with the exception of the Titan’s largest sea, Kraken Mare, which not only has a big name but also contains about 80 percent of the moon’s surface fluids,” said Valerio Poggiali, scientist Associate at the Cornell Center for Astrophysics and Planetary Research. Dr. Poggiali is the lead author of a paper describing the new depth measurements in the Journal of the American Geophysical Union.
NASA recently announced that it would launch a drone called Dragonfly to Saturn’s moon in 2026. Proposals have also been made for an orbiter, a floating probe that could splash into a lake, even a robotic submarine.
“The Titan submarine is still operational,” said Dr. Poggiali in an email, although it is unlikely to happen until next Titan summer around 2047. By then there will be more ambient light and the submarine could possibly continue to communicate with a direct connection to earth without a circulating radio relay.
Titan is, in some ways, the strangest place in the solar system and also the world that most closely resembles ours. Like Earth, it has a thick atmosphere made mostly of nitrogen (the only moon that has a large atmosphere at all), and like Earth, it has weather, rain, rivers, and seas.
But in this world it rains gasoline when it rains. Hydrocarbon material drifts down like snow and is formed into dunes by nitrogen winds. Rivers have carved canyons through mountains of frozen soot, and layers of ice float on subterranean oceans of ammonia. The prevailing surface temperature is minus 290 degrees Fahrenheit. A chemical mud that optimistic astronomers call “prebiotic” creeps under an oppressive brown sky. Aside from Earth, Titan is the only world in the universe known to have liquid on its surface – with all that could mean.
Astrobiologists have been eager to take a closer look at this world since Voyager I shot past it in 1980, radiating evidence that its smoggy atmosphere was four times as dense as ours. Time, technology, and human ingenuity have since shown that the cloudy world is a natural wonderland.
The northern regions of Titan are criss-crossed with a network of lakes and rivers. The largest of them, called Kraken Mare, is larger than all of North America’s great lakes combined, after a Nordic monster.
The Cassini orbiter has been buzzing around the Saturn system for 13 years, mapping these features in detail.
On August 21, 2014, as Cassini passed about 600 miles over the northern realms of Titan, he used his radar altimeter to measure the depths at Kraken Mare and Moray Sinus, an estuary on the north coast of the sea. Engineers have been able to measure the depths of the seas by noting the delay between the radar bouncing off the surface and the bouncing off the ocean floor.
Moray Sinus found to be about 280 feet deep, but there was no return echo from the octopus floor; The lake was either very, very deep, or it absorbed 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 1,000 feet,” concluded Dr. Poggiali.
Another big surprise is the composition of Kraken Mare. Scientists had expected it to contain relatively more ethane, which is denser than methane than Titan’s northernmost sea, Ligeia Mare.
In prevalent models of titanium hydrology, Dr. Poggiali, the presence of methane-nitrogen rain increases with latitude. This would lead to the composition of the “polar-facing seas” being richer in methane. “In simple terms, ethane is a little like salt in the ocean’s water,” he said.
He added: “The composition we derived for the fluid that fills Moray Sinus, this large bay in the northern part of Kraken Mare, is certainly quite surprising. We expected it would definitely have more ethane in it. Instead, we found that the Kraken is much more similar to Ligeia Mare, the second largest sea on Titan. This has a significant impact on the functioning of the water cycle. “There could be more ethane in the southern parts of the octopus mare, but the data we have doesn’t go that far.
This is more than just an abstract planetary science. According to scientists like Dr. Poggiali is titanium a laboratory where chemistry could have learned over millions of years to generate energy and store information. “These are processes that have also taken place on our planet, but have left no traces! As you can probably see, to better understand the mystery of life, we must return to Titan. ” he said.
Like an old captain sitting on the dock, Dr. Poggiali examines the possible voyages of a planned 20-foot NASA submarine. The voyage would begin in the center of Kraken Mare and continue as far as Moray Sinus, where the submarine would measure tides and compositions for three weeks before crossing the coasts, crossing the Bayta Fretum strait, and through a throaty passage called the Seldon Fretum going south.
During these explorations, the ship regularly mapped and surveyed the ocean floor, collecting detailed images of the coastline whenever possible. Titan’s surface gravity is less than that of Earth, and methane is less dense than water, allowing a small submarine to go deeper without being crushed by pressure as it would in a terrestrial sea of salt water.
In addition, Dr. Poggiali, since methane is transparent to radio waves, the submarine could potentially transmit data directly to Earth while it is still underwater. In total, the small submarine could travel 2,000 miles under the sea at a speed of one foot per second in 90 days, according to a NASA website describing the proposed submarine.
In the meantime, I can hardly be blamed for still dreaming of giant Titanic squids cavorting in this freezing cosmic aquarium made of natural gas.
Since the inception of the space program, cosmic visionaries have described space as “the new sea,” as President John F. Kennedy put it in a 1962 speech at Rice University. He never thought we could actually sail under it.