Proposed methane based life on Titan is just one example of life “not as we know it”

Yesterday, researchers at Cornell University made headlines by suggesting the possibility of Methane based life which could exist on Saturn’s largest moon Titan. The theoretical life form, however, is only the latest of many proposed forms of life which could conceivably exist in environments entirely unlike Earth’s.

There is a tendency for astrobiologist to focus on “Earth-like” planets to search for life “as we know it.” After all, researchers have plenty of places to look even with those limitations. According to Physics.org, there are two billion planets in our galaxy capable of supporting out kind of life and 22% of those have at least one planet candidate. That means 440 million potential Earth-like planets capable of hosting “life as we know it”.

However, our water and oxygen dependent, carbon based life form and all of our relatives on Earth are far from being the only possible form of life.

James Stevenson, a graduate student in chemical engineering at Cornell and one of the authors of the paper in the February 27 edition of the journal Science Advances, said that he was partially inspired by Isaac Asimov’s work on the subject.

In his 1962 essay on the topic, “Not as We Know It,” Asimov, the scientist, teacher and author of more than 200 books, laid out the case for other forms of life.

“For life-as-we-know-it, water is the indispensable background against which the drama is played out, and nucleic acids and proteins are the featured players. Hence any scientist, in evaluating the life possibilities on any particular world, instantly dismisses said world if it lacks water; or if it possesses water outside the liquid range, in the form of ice only or of steam only,” writes Asimov before going on to lay out a wide variety of possibilities for life evolving in a number of different environments.

In the end he lays out half-a-dozen possibilities, including our own before concluding that his own list is probably incomplete.

The Cornell University team lays out the case for life on Titan based on “azotosome,” from the Greek word for nitrogen “asset”. In their research they demonstrate the chemical viability of the cell would be capable of evolving in methane at temperatures approaching 300 degrees Fahrenheit below zero.

“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 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, in a statement.

So the theoretical “azotosome” is now added to the list of possible life forms. A good overview of the list to date is available on Wikipedia. The entry “Hypothetical types of biochemistry” has an extensive bibliography of sources and lists dozens of possibilities, from the silicon based life, a much discussed and popular theory, to the dust and plasma based life described by Vadim N. Tsytovich and colleagues in 2007.

For a brief period, in 2011, scientists even thought that they had found an example of “life, not as we know it.” The rod shaped bacteria, GFAJ-1, was thought to be able to be able to use arsenic to build its DNA, RNA, proteins, and cell membranes. Unfortunately, this later proved not to be the case.

Despite that false alarm, well known modern advocates for truly alien forms of life include Stephen Hawking and Neil deGrasse Tyson.

All of this does raise other questions however. The universe is believed to be 13.8 billion years old, our solar system is believed to be less than 5 billion years old and our species really only diverged from the rest of the animal kingdom about 15,000 years ago. We’ve been practicing “science” for about 500 years and took our first steps into space about 50 years ago.

As Enrico Fermi asked, if all of this is true and there are an estimated 440 million Earth-like planets out there and ours is only one of many potential forms of life then where, exactly, is everyone and why is extraterrestrial life so difficult to find?

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