On Earth, water means life so when astrobiologists go looking for life beyond Earth they naturally start by looking for liquid water. There is no hard and fast rule however that says that ours is the only kind of life out there.

Life “as we know it” requires water but we’re dealing with a sample size of one. Until we have more examples to work with, there is no knowing for sure where other forms of life could evolve.

Recently, a team of researchers has modeled a methane based, oxygen free form of life that can metabolize and reproduce in a way that is similar to organisms on Earth. The type of life, in other words, that could conceivably exist on Saturn’s moon Titan.

Titan is a Saturn’s largest moon and the second largest in our solar system. It is also the only moon known to have a thick atmosphere. It has a rocky surface and is brutally cold by our standards, with temperatures reaching -290 Fahrenheit. Despite the cold, Titan is covered in large, deep lakes of liquid methane.

Taking an approach that is both creative and rigidly rooted in science, chemical engineers and astronomers created a template for life that could thrive in Titan’s harsh environment.

The team’s theorized cell membrane is composed of organic nitrogen compounds and capable of functioning in liquid methane that approaches -300 degrees Fahrenheit.

Jonathan Lunine, a co-author of the paper, is an expert on Saturn’s moons and worked as a interdisciplinary scientist on NASA’s Cassini-Huygens missions. It was those missions that confirmed the existence of liquid methane-ethane seas on Titan. Interested in the possibility of life in such an environment, Lunine sought assistance from Cornell faculty with a particular expertise in chemical modeling.

Lunine recruited Paulette Clany, a chemical molecular dynamics expert and James Stevenson, a graduate student in chemical engineering.

“We’re not biologists, and we’re not astronomers, but we had the right tools. Perhaps it helped, because we didn’t come in with any preconceptions about what should be in a membrane and what shouldn’t. We just worked with the compounds that we knew were there and asked, ‘If this was your palette, what can you make out of that,’” said Clancy in a statement.

Life on Earth is based on the “phospholipid bilayer membrane”, a strong, permeable, water based, vesicle that holds the organic matter of cells. Membranes of this type are called liposome and conditions right for the creation of liposomes are what astronomers are looking for on exoplanets and moons in this solar system and beyond.

What, the researchers asked themselves, if the cells were based instead on methane with it’s much lower freezing point. They named their theorized membrane an “azotosome,” from the Greek word for nitrogen “asset”.

The theoretical cell is made from molecules known to exist on Titan such as nitrogen, hydrogen and carbon but the model demonstrates the same stability and flexibility that the liposome does on Earth.

According to the prepared statement, the researchers “employed a molecular dynamics method that screened for candidate compounds from methane for self-assembly into membrane-like structures. The most promising compound they found is an acrylonitrile azotosome, which showed good stability, a strong barrier to decomposition, and a flexibility similar to that of phospholipid membranes on Earth. Acrylonitrile – a colorless, poisonous, liquid organic compound used in the manufacture of acrylic fibers, resins and thermoplastics – is present in Titan’s atmosphere.”

The study is available in the February 27 edition of the journal Science Advances.

The next step for the researchers is to try and demonstrate how these cells would behave in a cold, liquid methane environment.

Lunine said that he hopes to one day test the team’s theories on Titan itself by “someday sending a probe to float on the seas of this amazing moon and directly sampling the organics.”

He may get his wish, earlier this month the NASA Innovative Advanced Concepts program unveiled a document describing a theoretical design for a robotic submarine that could be dropped into the Titan’s lakes.

“Measurement of the trace organic components of the sea, which perhaps may exhibit prebiotic chemical evolution, will be an important objective, and a benthic sampler (a robotic grabber to sample sediment) would acquire and analyze sediment from the seabed. These measurements, and seafloor morphology via sidescan sonar, may shed light on the historical cycles of filling and drying of Titan’s seas. Models suggest Titan’s active hydrological cycle may cause the north part of Kraken to be ‘fresher’ (more methane-rich) than the south, and the submarine’s long traverse will explore these composition variations,” said the authors of the conceptual document.

The proposed drone submarine mission, however, is still many years off under the best of circumstances.