clock menu more-arrow no yes mobile

Filed under:

Saturn’s moon Titan has a key ingredient that could be used to cook up life

New, 8 comments

How to form cell membranes in lakes of methane

A near-infrared color image of Titan’s north pole, taken by NASA’s Cassini spacecraft.
Image: NASA

Saturn’s moon Titan harbors a key chemical ingredient that may allow organisms to exist on this distant, chilly world. Astronomers have spotted a molecule in Titan’s atmosphere that could be instrumental in the formation of cells, which are a crucial building block of life. That means the molecule — and possibly some form of cellular life — might be located on the moon’s surface as well.

Researchers have suspected for a while that Titan might have this compound, called vinyl cyanide. NASA’s Cassini probe, which has been exploring the Saturn system for 13 years, found hints of the molecule when sniffing out the moon’s atmosphere, but its measurements haven’t been conclusive. Now, astronomers using the Atacama Large Millimeter Array, or ALMA, observatory in Chile say they have definitely measured a large amount of vinyl cyanide in the upper atmosphere. They’ve detailed their findings in the journal Science Advances.

On Earth, the outer layer of most cells — called membranes — are made up of fatty molecules called lipids. But lipids can’t form on Titan: they need liquid water to exist and the moon’s temperatures hover around -290 degrees Fahrenheit on the surface. However, Titan has liquid methane lakes, and astronomers have wondered if these liquids could take the place of water to build other forms of organic life. So in 2015, scientists used computer simulations to figure out what compounds could form stable cell membranes in the chilly lakes of Titan. And vinyl cyanide appeared to be the best candidate.

Radar images from NASA’s Cassini spacecraft that show lakes and depressions on Titan’s surface.
Image: NASA

Titan has a big appeal as a place to look for life elsewhere in our Solar System. Aside from its tantalizing lakes, the moon has a thick atmosphere, predominantly made up of nitrogen and other compounds commonly associated with life here on Earth. Detecting vinyl cyanide is a good reason to continue exploring Titan to see what might by lurking on its surface. “This is a far cry from saying [life] definitely happens on Titan and these cells are involved in some kind of primitive life,” co-author Martin Cordiner, an astrochemist at NASA’s Goddard Space Flight Center, tells The Verge. “But it gives us a starting point in that discussion. If there was going to be life in Titan’s oceans, then it’s plausible vinyl cyanide could be a component of that.”

The discovery was made possible by ALMA, one of the most sensitive telescopes in the world. Made up of 66 different individual telescopes in Chile’s Atacama Desert, the observatory is great for detecting super cold gases in space by measuring the radio waves these gases emit. In Titan’s atmosphere, the various gas molecules are constantly rotating, jumping back and forth from one level of energy to another. And whenever a molecule goes from a high-energy level to a lower one, it releases a radio wave. Different types of molecules emit waves at different types of frequencies. ALMA was able to figure out how much vinyl cyanide was present by measuring how many waves were coming off of Titan at a certain frequency.

The telescopes that make up ALMA.
Image: ESO / B. Tafreshi

The researchers only spotted the compound in the moon’s upper atmosphere, but vinyl cyanide might be in the lakes below as well. Scientists think that methane goes through a weather cycle similar to the one on Earth. The methane forms into droplets in the atmosphere, which periodically fall to the surface as rainfall. The vinyl cyanide may be hitching a ride on this rain and traveling down from the atmosphere to the lakes, where it potentially forms pretty stable cell membranes.

Based on the ALMA findings, it looks like there’s a lot of vinyl cyanide to do that. The researchers measured so much of the compound, that 10 million cell membranes per cubic centimeter could be present in one of Titan’s largest lakes, Ligeia Mare. These membranes could be pretty flexible, too, according to Paulette Clancy, a professor of chemical and biomolecular engineering at Cornell University, who worked on the original computer simulation. This is key for the cells to divide and reproduce. “The flexibility of that membrane would be the same as the flexibility for our cell membranes on Earth, which is really cool because they’re totally different in chemical composition,” Clancy tells The Verge.

A computer model of a theoretical membrane that could exist on Titan, made of vinyl cyanide.
Image by James Stevenson

Of course, the idea that cell membranes even exist on Titan is all theoretical for now. The only way to know for sure is to send another probe to the moon, perhaps one that could float on the methane lakes and measure what’s inside. “There’s been some discussion of maybe sending a boat or something like that to Titan to observe what’s really going on in the lakes,” says co-author Maureen Palmer, an astrochemist at NASA’s Goddard Space Flight Center. “That’d be really cool to see.”

For now, ALMA’s discovery helps paint a more vivid portrait of just how interesting Titan is. Vinyl cyanide is a fairly complex molecule, made up of seven elements. It’s difficult to find such complicated molecules far away from Earth. But many of the moons in the outer Solar System, such as Jupiter’s moon Europa or Saturn’s other moon Enceladus, are turning out to harbor complex chemicals and processes we thought only existed on Earth. “As we explore more in the outer Solar System, these moons of the giant planets reveal to us that they are much more fascinating environments than we could have ever imagined,” says Cordiner. “Complex chemistry is not unique to Earth.”