Titan's atmosphere recreated in a laboratory on Earth

Scientists believe the best place to look for evidence of extraterrestrial life is Mars. However, this is far from

the only place.In addition to the many extrasolar planets that have been identified as “potentially habitable,” there are many other candidates right here in our solar system. These include many icy moons that are believed to have inland oceans that could contain life.

Much of what we know about Titan todayassociated with the spacecraft Cassini, which orbited Saturn from 2004 to 2017 and completed its mission by plunging into the planet's atmosphere. During this time, Cassini made many direct measurements of Titan's atmosphere, discovering a surprisingly Earth-like environment. In fact, this is the only other body in the solar system in which there is a dense nitrogen atmosphere and organic processes take place.

What's particularly interesting is that scientistsbelieve that about 2.8 billion years ago, the Earth's atmosphere could be similar. This coincides with the Mesoarchean era, the period when photosynthetic cyanobacteria created the first reef systems and slowly converted Earth's atmospheric carbon dioxide into oxygen gas (which eventually led to the current balance of nitrogen and oxygen).

Although the surface of Titan is believed to containclues that could improve our understanding of how life originated in our solar system, getting a clear picture of this surface has been a challenge. The reason for this has to do with Titan's atmosphere, which is riddled with a dense photochemical haze that scatters light.

"Titan's haze is composed of nanoparticles, consisting ofa wide variety of large and complex organic molecules containing carbon, hydrogen and nitrogen. These molecules are formed in a cascade of chemical reactions when (ultraviolet and cosmic) radiation hits a mixture of methane, nitrogen and other gases. in an atmosphere similar to that of Titan. "

Leo Gross and Natalie Carrasco, IBM

As a result, scientists still don't know much aboutthe processes that govern Titan's atmosphere, including the precise chemical structure of the large molecules that make up this haze. For decades, astrochemists have conducted laboratory experiments with similar organic molecules known as tholins, a term derived from the Greek word for "turbid."

Tolins belong to a wide range of organiccarbon-containing compounds that are formed when exposed to solar ultraviolet radiation or cosmic rays. These molecules are common in the outer solar system and are commonly found in ice bodies, where the surface layer contains methane ice that is exposed to radiation. Their presence is indicated by a ruddy surface or sepia-colored spots.

For the sake of their research, a group led by Schultz and Maillard conducted an experiment in which they observed tholins at various stages of formation in the laboratory.

“We filled the stainless steel vessel with the mixturemethane and nitrogen, and then initiated chemical reactions through an electrical discharge, thereby simulating conditions in Titan's atmosphere. We then analyzed more than 100 of the resulting molecules that make up the titanium thicknesses in our laboratory in Zurich, taking atomic-resolution images of about a dozen of them using our homemade low-temperature atomic force microscope. ”

Leo Gross and Natalie Carrasco, IBM

Taking apart molecules of different sizes, the teamgot an idea of ​​the different stages of growth of these molecules, as well as what their chemical composition looks like. In fact, they observed a key component of Titan's atmosphere as it formed and accumulated, creating the famous fog effect.

Scientists observe molecular architecture for the first timesynthetic compounds similar to those believed to cause an orange haze in Titan's atmosphere. What's more, their findings could shed light on a mysterious methane-based hydrological cycle. On Earth, this cycle consists of the transition of water from a gaseous state (water vapor) to a liquid state (rain and surface water). On Titan, the same cycle occurs with methane, which is transferred from atmospheric methane and falls as methane rain, forming the famous hydrocarbon lakes.

In this case, the results of the research groupcould reveal the role that chemical haze plays in Titan's methane cycle, including whether these nanoparticles can float on its methane lakes. In addition, these discoveries could show whether similar atmospheric aerosols helped create life on Earth billions of years ago.

Molecular structures are known to be goodabsorbers of ultraviolet light. This, in turn, means that the haze could act as a shield, protecting DNA molecules on the early Earth's surface from damaging radiation.

NASA plans to send to Titan by the 2030sa robotic rotorcraft called Dragonfly to explore its surface and atmosphere and look for possible signs of life. As always, theoretical work and laboratory experiments conducted in the meantime will allow scientists to narrow their focus and increase the chances that the mission, once it arrives, will find what it is looking for.

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