The dunes on Titan might be made of organic compounds

Titan's dunes (Image courtesy University of Hawaii at Manoa)
Titan’s dunes (Image courtesy University of Hawaii at Manoa)

An article published in the journal “Science Advances” reports a study that offers some answers to the mystery of the origin and composition of the dunes on Titan, one of the moons of the planet Saturn particularly interesting for many reasons that include the formation of many organic compounds. A team of researchers led by physical chemist Ralf I. Kaiser of the University of Hawaii at Manoa examined data collected during the Cassini-Huygens mission and computer simulations whose results indicate that acetylene exposed to cosmic rays can form materials that make up Titan’s dunes.

The Cassini-Huygens mission ended on September 15, 2017 with the destruction of the Cassini space probe in the atmosphere of the planet Saturn, leaving behind an enormous amount of data collected over the years. Titan was from the beginning of the mission one of the most interesting subjects of study for a series of reasons that include the complex compounds that are formed on that moon. Titan’s geology is also interesting and the dunes that form on its surface and can be as high as 100 meters are one of the mysteries that remained to be solved after the end of the mission.

On Earth, dunes are made mainly from silicates, on Titan they’re made of dark organic compounds on whose origin there were various hypotheses but far from complete such as the one about the possible composition in hydrocarbons like the ones present in this moon’s lakes. This new research offers a more complete solution that can also be useful in research on Kuiper belt objects.

On Earth, acetylene is a gas used for welding, on Titan, at such temperatures that it’s frozen. The researchers exposed acetylene ice blocks to a replica of the effects of cosmic rays. The result is the conversion of acetylene into organic molecules such as benzene and naphthalene. These processes can also occur in interstellar space, as reported in an article published in the journal “Nature Communications” in September 2019.

Matthew Abplanalp, another of the authors of this research, explained that Titan’s dunes represent the dominant sink on Titan’s surface in organic chemistry. Consequently, discovering the origin and chemical pathways that form the organic dune materials is vital not only to understand Titan’s chemical evolution but also to understand how similar the chemical processes on Titan and on Earth may have been before life emerged on Earth.

Ralf I. Kaiser outlined the situation of the processes that eventually provide the molecular building blocks not only for Titan’s organic dunes but also for organic compounds on other airless bodies such as the dwarf planet Makemake in the Kuiper belt. The synthesis of polycyclic aromatic hydrocarbons (PAHs) from acetylene ice represents a fundamental shift from the current perception of their formation only in the gas phase at temperatures of thousands of degrees such as in combustion processes.

This research not only confirms that Titan is a really interesting moon for the chemical processes that take place there but shows how certain complex reactions can take place even at very low temperatures thanks to the energy of the particles that make up cosmic rays. NASA is planning a mission with a flying robot called Dragonfly to explore Titan and the interest in studies of other bodies in the Kuiper belt could increase.

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