NASA discovers a “very strange” molecule in Titan’s atmosphere

NASA Scientists identified a molecule in Titan’s atmosphere that was not detected in any other atmosphere. In fact, many chemists have probably barely heard of it or even knew 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 potentially make or feed life on titanium.

Researchers found C.₃H.₂ by using a radio telescope observatory in northern Chile known as the Atacama Large Millimeter / Submillimeter Array (ALMA). They noticed C.₃H.₂, which is made up of carbon and hydrogen while looking through a spectrum of unique light signatures collected by the telescope; These revealed the chemical makeup of Titan’s atmosphere through the energy its molecules emitted or absorbed.

“When I realized I was looking at cyclopropenylidene, my first thought was,” Well, that’s really unexpected, “said Conor Nixon, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland who led the ALMA search. The results of his team were announced on October 15, 2020 in the Astronomisches Journal.

Although scientists found C.₃H.₂ In pockets across the galaxy it was a surprise to find them in one atmosphere. This is because cyclopropenylidene can easily react with other molecules it comes in contact with, forming different species. So far, astronomers have found C.₃H.₂ only in clouds of gas and dust floating between star systems – in other words, regions that are too cold and diffuse to allow many chemical reactions.

But dense atmospheres like that of Titan are beehives of chemical activity. This is a major reason scientists are interested in this moon, which is the target of NASA’s upcoming dragonfly mission. Nixon’s team was able to identify small amounts of C.₃H.₂ in the case of Titan, probably because they looked into the upper layers of the lunar atmosphere, where there are fewer other gases for C.₃H.₂ Interact with something. Scientists don’t yet know why cyclopropenylidene would appear in Titan’s atmosphere, but not in any other atmosphere. “Titan is unique in our solar system,” said Nixon. “It has proven to be a treasure trove of new molecules.”

The largest of SaturnWith its 62 moons, Titan is a fascinating world that is in some ways most similar to the Earth we found. Unlike every other moon in the solar system – there are more than 200 – Titan has a thick atmosphere four times denser than Earth’s, plus clouds, rain, lakes and rivers, and even an underground ocean of salt water.

The Titan atmosphere, like Earth, consists mainly of nitrogen with a hint of methane. When methane and nitrogen molecules break apart under the light of the sun, their atoms unleash a complex web of organic chemistry that has fascinated scientists and has put this moon at the top of the list of key targets in NASA’s search for present or past life in the solar system .

“We’re trying to find out if titanium is habitable,” said Rosaly Lopes, senior research scientist and titanium expert at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “So we want to know which compounds from the atmosphere reach the surface and whether this material can then get through the ice crust into the ocean, because we believe that habitable conditions prevail in the ocean.”

The types of molecules that could sit on Titan’s surface could be the same ones that formed the building blocks of life on Earth. At the beginning of its history, 3.8 to 2.5 billion years ago, when methane filled the earth’s air instead of oxygen, the conditions here could have been similar to those on Titan today, scientists suspect.

“We think of titanium as a real-world laboratory where we can see chemistry similar to what we saw on old Earth when life first came here,” said Melissa Trainer, an astrobiologist with NASA Goddard. Trainer is the assistant principal researcher of the Dragonfly mission and head of an instrument on the Dragonfly rotary wing that analyzes the composition of the titanium surface.

“We’re going to look for larger molecules than C.₃H.₂“Said Trainer,” but we need to know what is happening in the atmosphere to understand the chemical reactions that cause complex organic molecules to form and rain to the surface.

Dragonfly is a NASA mission aimed at researching the chemistry and habitability of Saturn’s largest moon, Titan. Photo credit: NASA Goddard Space Flight Center / Applied Physics Laboratory, Johns Hopkins University

Besides benzene, cyclopropenylidene is the only other “cyclic” or closed molecule that has so far been found in the titanium atmosphere. Although C.₃H.₂ It is not known to be used in modern biological reactions. Such closed-loop molecules are important as they form the backbone rings for the nucleobases of DNA, the complex chemical structure that carries the genetic code of life, and RNA, another critical link for the functions of life. “Their cyclical nature opens up this additional branch of chemistry that you can use to build these biologically important molecules,” said Alexander Thelen, a Goddard astrobiologist who worked with Nixon to find C.₃H.₂.

Scientists like Thelen and Nixon are using large and highly sensitive terrestrial telescopes to search for the simplest life-related carbon molecules they can find in Titan’s atmosphere. Benzene was thought to be the smallest unit of complex, ring-shaped hydrocarbon molecules found in a planetary atmosphere. But now, C.₃H._2, with half the carbon atoms of benzene appears to have taken its place.

Nixon’s team used the ALMA observatory to take a look at Titan in 2016. They were surprised to find a strange chemical fingerprint that Nixon identified as cyclopropenylidene by searching a database of all known molecular light signatures.

To verify that the researchers actually saw this unusual compound, Nixon rummaged through research reports published from analysis of data by NASA Cassini Spaceship that made 127 close passes of Titan between 2004 and 2017. He wanted to see if an instrument on the spaceship that was sniffing out the chemical compounds around Saturn and Titan could confirm his new finding. (The instrument – called a mass spectrometer – picked up evidence of many mysterious molecules in titanium that scientists are still trying to identify.) Indeed, Cassini had found evidence of an electrically charged version of the same C molecule₃H.₃⁺.

Since it is a rare find, scientists are trying to learn more about cyclopropenylidene and how it interacts with gases in the titanium atmosphere.

“It’s a very strange little molecule, so it won’t be the kind you learn in high school chemistry or undergraduate chemistry,” said Michael Malaska, a JPL planetary scientist who worked in the pharmaceutical industry before joining fell in love with titanium and switched careers to study it. “It won’t be something down here on earth that you will encounter.”

But, said Malaska, and found molecules like C.₃H.₂ is really important to see the bigger picture of Titan: “Every little piece and piece that you can discover can help you put together the huge puzzle of all the things that are going on there.”

Reference: “Detection of cyclopropenylides on titanium 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, Astronomisches Journal.
DOI: 10.3847 / 1538-3881 / abb679