Titan: the moon raining plastics & flowing with lakes of liquified natural gas

Titan: the moon raining plastics & flowing with lakes of liquified natural gas

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Roughly the size of the planet Mercury, Titan is the largest moon of Saturn and the second largest moon in the solar system after Jupiter’s moon Ganymede. Wrapped in a thick, frothy orange atmosphere made primarily of nitrogen and a bit of methane, Titan is the only other place besides Earth known to have liquid on its surface. Akin to Earth’s water cycle, Titan has a “methane cycle” with liquid methane and ethane raining from clouds, filling lakes and seas. With its extremely cold temperatures, water ice replaces rock. Titan’s surface is approximately -179C, cold enough for methane to liquify, flow across its surface, and evaporate back into its forever-sunset sky.

Because of its smoglike organic haze, daytime on Titan is probably only about as bright as twilight on Earth. Titan’s atmosphere is two times as thick as Earth’s and four times denser, with 86% less gravity than Earth. Given the thick atmosphere and low gravity, you could fly like a bird with a set of wings strapped to your arms. NASA’s Cassini spacecraft made 127 flybys of Titan over 13 years exploring Saturn, in addition to dropping a European Space Agency spacecraft called Huygens through Titan’s atmosphere in 2005, finally unveiling the moon’s incredible, complex surface hidden for so long.

Instead of sand or dirt, Titan’s surface is covered in non-silicate granules. The granules are essentially plastics, formed in the atmosphere as hydrocarbons produce longer chained molecules that fall to the surface as ethane, ethylene, propane, etc. These include propylene, which is found in common household plastics like reusable sandwich containers. Due to a unique combination of factors like Titan’s bone-dry air and surface composed of low-density volatile vapors, the plastic granules are electrically charged. These staticcling granules might feel similarly to sticking your hand into a box of packing peanuts. Sculpted not only by wind, but by electrostatic forces, this “electric sand” creates majestic dunes similar in shape and size to those found in Earth’s deserts.

Titan’s surface is carved by flowing liquid natural gas, filling river channels and great lakes. However, standing on its surface is where you would truly feel “underwater.” Standing on the surface of Titan: The moon raining plastics & flowing with lakes of liquified natural gas, you would feel about 50% more pressure than you would on Earth, like diving fifteen feet into the ocean. When the Huygens probe landed on Titan in 2005, it took three hours to descend through Titan’s thick atmosphere. The physical exertion required to walk on Titan might feel like swimming through water.

Titan’s complex chemistry makes it a top candidate for potentially finding life in the cosmos. The rivers, lakes and seas of hydrocarbon liquid might serve as a habitable environment on the moon’s surface, though any life there would likely be very different from life as we know it. Although there is so far no evidence for life on Titan, there is compelling science suggesting some possibilities of life.

In cells, glucose reacts with oxygen, producing carbon dioxide and water. Life living in Titan’s seas of hydrocarbon liquid could possibly intake hydrogen instead of oxygen, react with acetylene instead of glucose, and produce methane rather than carbon dioxide. Comparably, methanogens (methane-producing bacteria) on Earth convert hydrogen, carbon dioxide and acetate to carbon dioxide and methane.

If methanogenic life existed on Titan in sufficient numbers, then a measurable effect on the hydrogen levels in Titan’s atmosphere should be observed. Interestingly, scientists have in fact found levels of hydrogen and acetylene near the moon’s surface to be lower than expected. The physics of diffusion expects higher concentrations of hydrogen in Titan’s upper atmosphere to float downward. However, near the surface the downward flowing hydrogen seems to disappear. Could this be the result of methanogenic life consuming hydrogen in Titan’s lakes?

Other factors like human error or meteorological processes could be just as probable. The absence of detectable acetylene on the surface could possibly be due to sunlight or cosmic rays transforming acetylene into more complex molecules. It is likely that non-biological chemical processes could explain these results, such as reactions involving mineral catalysts.

Apart from curious hydrogen measurements, other compelling science might suggest biology on Titan. An experiment conducted by a University of Arizona-led team of scientists found that when energy is applied to a combination of the same gases found on Titan, some of the compounds produced include the five nucleotide bases that constitute the building blocks of DNA and RNA, as well as amino acids, the building blocks of protein: the most important ingredients of life on Earth.

Titan, with its methane seas, ice rocks and electric sand, is in some ways the most similar world to Earth that we have found. This is why NASA is preparing to send the helicopter-like spacecraft Dragonfly to explore this miraculous moon. Slated for launch in 2026, when Dragonfly arrives on Titan in 2034 it will use the dense atmosphere to fly like a drone. During its 2.7 year mission, Dragonfly’s instruments will study how far pre-life chemistry may have progressed. Its instruments will advance our search for the building blocks of life, investigating the moon’s atmospheric and surface properties, liquid reservoirs, and areas where water and complex organics may have existed together for tens of thousands of years.

With the exciting prospects of this rotorcraft lander mission, we may learn more than ever before about how far prebiotic chemistry has progressed in a world beyond Earth. Along with a bit of luck, we might soon discover chemical signatures for hydrocarbon-based life.

About author

Dalia Kirshenblat

Dalia Kirshenblat is a proud graduate of Ithaca College’s class of 2020 with a degree in Science Writing and Communication. Dalia has extensive experience working with museums like the American Museum of Natural History in New York and the Ithaca Sciencenter. Dalia also works with science outreach organisations like Cornell University’s Spacecraft Planetary Imaging Facility (SPIF) and the Alex Hayes research group COMPASSE: Comparative Planetology & Solar System Exploration. Dalia is currently writing an astrobiology book for children and young adults.

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