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Using highly sensitive spectroscopic observations from the Atacama Large Millimeter / submillimeter Array (ALMA), astronomers have detected a small cyclic molecule called cyclopropenylidene (C3Htwo) in the atmosphere of Titan, Saturn’s largest moon.
This composite image shows an infrared view of Titan. In this image, blue represents wavelengths centered at 1.3 microns, green represents 2.0 microns, and red represents 5.0 microns. A view at visible wavelengths would only show Titan’s hazy atmosphere; the near-infrared wavelengths in this image allow Cassini’s view to penetrate the haze and reveal the moon’s surface. The view is looking toward terrain that is primarily in the Saturn-facing hemisphere of Titan. Image credit: NASA / JPL-Caltech / Space Science Institute.
“When I realized I was looking at cyclopropenylidene, my first thought was, ‘Well, this is really unexpected,’ said Dr. Conor Nixon, a planetary scientist at NASA’s Goddard Space Flight Center.
“It’s a very strange little molecule, so it won’t be the kind you learn in high school chemistry or even undergraduate chemistry,” said Dr. Michael Malaska, planetary scientist at NASA’s Jet Propulsion Laboratory. .
“Here on Earth, it won’t be something you are going to encounter.”
“But finding molecules like cyclopropenylidene is really important to see the big picture of Titan. Every little piece and part you can discover can help you put together the huge puzzle of all the things that happen there. “
Although astronomers previously found cyclopropenylidene in clouds of gas and dust, such as the Taurus Molecular Cloud, throughout the Milky Way, finding it in an atmosphere came as a surprise.
That’s because this molecule can easily react with other molecules that it comes into contact with and form different species.
Dr. Nixon, Dr. Malaska, and their colleagues were able to identify small amounts of cyclopropenylidene on Titan likely because they were looking at the upper layers of the moon’s atmosphere, where there are fewer other gases that cyclopropenylidene interacts with.
“Titan is unique in our Solar System. It has proven to be a treasure trove of new molecules, “said Dr. Nixon.
“We’re trying to find out if Titan is habitable,” said Dr. Rosaly Lopes, senior research scientist and Titan expert at NASA’s Jet Propulsion Laboratory.
“So we want to know what compounds in the atmosphere make it to the surface and then if that material can make its way through the ice crust to the ocean, because we think the ocean is where the habitable conditions are.”
The types of molecules that could be sitting on Titan’s surface could be the same ones that made up the building blocks of life on Earth.
At the beginning of its history, 3.8 to 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.
“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 Dr. Melissa Trainer, an astrobiologist at NASA’s Goddard Space Flight Center.
“We will look for molecules larger than cyclopropenylidene, but we need to know what is happening in the atmosphere to understand the chemical reactions that lead to the formation of complex organic molecules and rain to the surface.”
Cyclopropenylidene is the only other cyclic molecule besides benzene that has been found in Titan’s atmosphere so far.
Although cyclopropenylidene is not known to be used in modern biological reactions, cyclic molecules such as this one are important because they form the backbone rings of DNA nucleobases, the complex chemical structure that carries the genetic code of life, and RNA, another critical element. composed for the functions of life.
“Their cyclical nature opens up this additional branch of chemistry that allows you to build these biologically important molecules,” said Dr. Alexander Thelen, an astrobiologist at NASA’s Goddard Space Flight Center.
An article on the findings was published in the Astronomical diary.
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Conor A. Nixon et al. 2020. Detection of cyclopropenylidene on Titan with ALMA. AJ 160, 205; doi: 10.3847 / 1538-3881 / abb679
