Learning The Secrets Of A Mysterious Misty Moon

 With its enticingly secretive surface blanketed by a dense golden-orange fog, Titan--the largest moon of Saturn--was long regarded as a mysterious, frigid moon-world. However, the Cassini-Huygens mission changed all that when the Huygens lander floated down to the foggy moon's surface in 2004, and gazed at Titan's well-hidden face behind its strange orange mask. Although the Cassini-Huygens mission ended in 2017, planetary scientists are still pouring over the treasure trove of information that it sent back to Earth before it was intentionally destroyed by mission scientists. In October 2019, a team of scientists led by a University of Hawaii (Manoa) chemistry professor and researcher, announced that they have been able to provide answers to important questions about the strange surface of Titan. The researchers say that they have unraveled the origin and chemical composition of Titan's alien dunes.

Physical chemist, Dr. Ralf I. Kaiser, and his colleagues, examined remote sensing data provided by Cassini-Huygens regarding Titan. Titan is the only Solar System body, other than Earth, that sports a solid surface, lakes and a substantial atmosphere with a pressure of approximately 1.5 atmospheres at surface level. Images and data provided by Cassini-Huygens revealed the existence of vast longitudinal dunes on that foggy orange moon-world. The dunes are located across Titan's equatorial deserts, and they reach lofty heights of up to 100 meters--making them similar in size to the Egyptian pyramids of Giza. However, while Earth's dunes are composed primarily of silicates, imaging studies revealed that Titan's dunes are made up of a different material. Titan's dunes were shown to contain dark organics that, until this new study, were of undetermined origin and chemical composition.

The University of Hawaii at Manoa (UH) team, which also included Dr. Matthew Abplanalp, then a graduate student at UH, discovered the existence of acetylene ice in Titan's dunes. Acetylene is a chemical used on Earth in welding torches. It exists in Titan's equatorial regions, but at low temperatures to proxies of high-energy Galactic cosmic rays. The scientists found a rapid cosmic-ray-driven chemistry which causes simple molecules like acetylene to experience a sea-change into more complex organic molecules like benzene and naphthalene. Naphthalene is a compound which is found in familiar mothballs on Earth, and it exists on Titan's exotic surface. These processes also occur in the space between stars (interstellar medium) on hydrocarbon rich layers of interstellar nanoparticles.

This new research has been published in the journal Science Advances under the title Low-temperature synthesis of polycyclic aromatic hydrocarbons in Titan's surface ices and on airless bodies.

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds that contain only carbon and hydrogen, and are composed of multiple aromatic rings.

The Strange Face Behind The Smoggy Orange Mask Of A Distant Moon

Titan is the largest moon of the ringed gas-giant planet, Saturn, as well as the second-largest moon in our Solar System. Only Ganymede of Jupiter is larger than Titan. Here, in the frigid realm of the quartet of majestic, giant, and gaseous outer planets--Jupiter, Saturn, Uranus, and Neptune--our Sun shines with a weaker fire than it does in the inner Solar System where Earth is situated--along with the three other solid and relatively small planets: Mercury, Venus, and Mars.

Titan is a hydrocarbon-tormented world, that bears an eerie resemblance to the way our own planet was, very long ago, before life emerged and evolved here (prebiotic). Like Earth, Titan experiences frequent downpours of rain, swirling seas, and eroding organic material. However, on Titan, it is not liquid water that fills its alien seas, rivers, and lakes with lovely little raindrops. On this strange smoggy moon-world, life-sustaining liquid water is replaced by weird, lazy, large drops of methane. The surface of Titan is pelted with a "rain of terror"--on Titan, it rains gasoline. On this strange moon, atmospheric molecules composed of methane are perpetually being torn apart by sunlight, and the resulting atmospheric smog floats down to the surface, where it accumulates as organic settlements that rapidly rob the atmosphere of methane. The surface of Titan is well-coated with the material of old atmospheres that have long since vanished.