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These infrared images of Saturn’s moon Titan represent some of the clearest global views of the moon’s frigid surface. The visualizations were created using 13 years of data acquired by the Visual and Infrared Mapping Spectrometer instrument aboard NASA’s Cassini spacecraft. Credits: NASA / JPL-Caltech / University of Nantes / University of Arizona
NASA scientists have identified a molecule in Titan’s atmosphere that has never been detected in any other atmosphere. In fact, many chemists probably have just heard of it or know how to pronounce it: cyclopropenylidene, or C.3H.2. Scientists say this simple carbon-based molecule could be a precursor to more complex compounds that could form or fuel possible life on Titan.
This image was returned on January 14, 2005 by the European Space Agency’s Huygens probe during its successful descent to the surface of Titan. This is the colored view that has been processed to add reflection spectra data and provide a better indication of the actual color of Titan’s surface.
Credits: NASA / JPL / ESA / University of Arizona
The researchers found that C3H.2 using an observatory radio telescope in northern Chile known as the Atacama Large Millimeter / submillimeter Array (ALMA). They noticed C3H.2, which is made of carbon and hydrogen, while sifting through a spectrum of unique light signatures collected by the telescope; these revealed the chemical composition of Titan’s atmosphere from the energy its molecules emitted or absorbed.
“When I realized I was looking at cyclopropenylidene, my first thought was, ‘Well, this is really unexpected,'” said Conor Nixon, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who said. led the ALMA research. His team’s findings were published on October 15, 2020 in Astronomical Journal.
Although the scientists found that C3H.2 in pockets across the galaxy, finding it in an atmosphere was a surprise. This is because cyclopropenylidene can easily react with other molecules it comes into contact with and form different species. Astronomers have so far discovered C.3H.2 only in the clouds of gas and dust that float between star systems – in other words, regions too cold and diffuse to facilitate many chemical reactions.
But dense atmospheres like that of Titan are hives of chemical activity. This is one of the main reasons scientists are interested in this moon, which is the destination of NASA’s next Dragonfly mission. Nixon’s team was able to identify small amounts of C.3H.2 to Titan probably because they were looking into the upper layers of the lunar atmosphere, where there are fewer other gases for C.3H.2 to interact with. Scientists do not yet know why cyclopropenylidene appeared in Titan’s atmosphere but not in any other atmosphere. “Titan is unique in our solar system,” Nixon said. “It has proven to be a treasure trove of new molecules.”
The largest of SaturnWith 62 moons, Titan is an intriguing world that is in some ways the most Earth-like we have found. Unlike any other moon in the solar system – there are more than 200 of them – Titan has a thick atmosphere that is four times denser than Earth’s, as well as clouds, rain, lakes and rivers, and even an underground saltwater ocean. .
Titan’s atmosphere is mainly composed of nitrogen, like Earth’s, with a hint of methane. When the molecules of methane and nitrogen break apart under the sun’s glow, their component atoms release a complex web of organic chemistry that has fascinated scientists and pushed this moon to the top of NASA’s list of most important research targets for the present or past life in the solar system.
“We’re trying to figure out if Titan is habitable,” said Rosaly Lopes, senior researcher and Titan expert at NASA’s Jet Propulsion Laboratory.JPL) in Pasadena, California. “So we want to know which compounds from the atmosphere make it to the surface, and then, if that material can cross the ice crust to the ocean below, because we think the ocean is where the habitable conditions are.”
The types of molecules that could be present on Titan’s surface could be the same ones that formed the building blocks of life on Earth. Early in its history, 3.8-2.5 billion years ago, when methane filled Earth’s air instead of oxygen, conditions here could have been similar to those on Titan today, scientists suspect.
“We think of Titan as a real-life laboratory where we can see chemistry similar to that of ancient Earth when life was taking hold here,” said Melissa Trainer, a NASA Goddard astrobiologist. Trainer is the Deputy Principal Investigator of the Dragonfly mission and chief of an instrument on the Dragonfly rotorcraft that will analyze the composition of Titan’s surface.
“We will look for molecules larger than C3H.2“Trainer said,” but we need to know what’s going on in the atmosphere to understand the chemical reactions that lead to the formation and rain of complex organic molecules.
Dragonfly is a NASA mission that aims to explore the chemistry and habitability of Saturn’s largest moon, Titan. Credit: NASA’s Goddard Space Flight Center / Johns Hopkins University Applied Physics Laboratory
Cyclopropenylidene is the only other “cyclic” or closed-loop molecule besides benzene that has so far been found in Titan’s atmosphere. Although C3H.2 not known to be used in modern biological reactions, closed loop molecules like this are important because they form the backbone rings for the nitrogenous bases of DNA, the complex chemical structure that carries the genetic code of life, e RNA, another compound critical to the functions of life. “Their cyclic nature opens up this extra branch of chemistry that allows you to build these biologically important molecules,” said Alexander Thelen, a Goddard astrobiologist who worked with Nixon to find C3H.2.
Scientists like Thelen and Nixon are using large, highly sensitive ground-based telescopes to search for the simplest life-bound carbon molecules they can find in Titan’s atmosphere. Benzene was considered to be the smallest unit of complex, ringed hydrocarbon molecules found in any planetary atmosphere. But now, C.3H.2, with half the carbon atoms of benzene, it appears to have taken its place.
Nixon’s team used the ALMA observatory to scan Titan in 2016. They were surprised to find a strange chemical fingerprint, which Nixon identified as cyclopropenylidene by searching a database of all known molecular light signatures.
Until now, cyclopropenylidene has only been detected in molecular clouds of gas and dust, such as the Taurus Molecular Cloud, which is a stellar nursery in the constellation of Taurus more than 400 light-years away. Recently, NASA scientist Goddard Conor Nixon, along with his team, found this unique molecule in Titan’s atmosphere; the first time it was detected outside a molecular cloud. Cyclopropenylidene is the only other closed-loop molecule besides benzene to have been detected in Titan. Closed-loop molecules are important because they form the backbone rings for the nitrogenous bases of DNA, the complex chemical structure that carries the genetic code of life, and RNA, another compound critical to life’s functions. Credits: Conor Nixon / NASA’s Goddard Space Flight Center
To double-check that the researchers were indeed seeing this unusual compound, Nixon carefully examined research papers published by NASA’s data analysis. Cassini spacecraft, which made 127 close passes of Titan between 2004 and 2017. He wanted to see if an instrument on the spacecraft that smelled the chemical compounds around Saturn and Titan could confirm his new result. (The instrument – called a mass spectrometer – has collected clues to many mysterious molecules on Titan that scientists are still trying to identify.) Indeed, Cassini had spotted evidence for an electrically charged version of the same molecule, C.3H.3+.
Since it is a rare discovery, scientists are looking to learn more about cyclopropenylidene and how it might interact with gases in Titan’s atmosphere.
“It’s a very weird little molecule, so it won’t be the kind you learn in high school chemistry or even college chemistry,” said Michael Malaska, a JPL planetary scientist who worked in the pharmaceutical industry before falling in love with Titan. and change careers to study it. “Down here on Earth, it won’t be something you will encounter.”
But, Malaska said, by finding molecules like C3H.2 it is very important to see the big picture of Titan: “Every little piece and part that you can discover can help you put together the huge puzzle of all the things that happen there”.
Reference: “Detection of Cyclopropenylidene on Titan with ALMA” by Conor A. Nixon, Alexander E. Thelen, Martin A. Cordiner, Zbigniew Kisiel, Steven B. Charnley, Edward M. Molter, Joseph Serigano, Patrick GJ Irwin, Nicholas A. Teanby and Yi-Jehng Kuan, October 15, 2020, Astronomical Journal.
DOI: 10.3847 / 1538-3881 / abb679
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