There are over two dozen exoplanets in our galaxy that have the potential to harbour life, not to mention the numerous other habitable worlds that could exist in the other 100 billion galaxies throughout the universe.
Considering the numbers, the chances for life existing beyond Earth look good. However, the chances of detecting that life are less certain.
Why? For one thing, we simply don’t know what that alien life will look like.
“It could be so utterly different that it could be staring us in the face and we would not be able to understand that it is life,” Christopher Adami, a professor of microbiology and molecular genetics at Michigan State University, told Business Insider.
Beyond carbon-based life
All life on Earth is carbon-based, meaning the organic molecules that comprise every living organism known to man contain carbon atoms bonded with other atoms. For example, one of the simplest organic compounds — methane — has one carbon atom and four hydrogen atoms.
But other lifeforms could be based on something else entirely. Take Saturn’s moon Titan, for example. It’s rich with lakes of liquid methane on the surface. These lakes could harbour methane-based life forms that are vastly different from the carbon-based life we have here on Earth. If our instruments for detecting life are only designed to test for life like us, however, we may never know if life on Titan, or other life with different chemistry on other worlds, exists.
Adami is working on a way around this problem. He presented his approach at the 2015 APS April meeting.
In the early ’90s, he helped develop a highly sophisticated computer program called Avida. The program studies how digital organisms — computer programs with the ability to self-replicate and mutate without human intervention — evolve over time. Scientists use programs like these to better understand the traits that drive Darwinian evolution. Their artificial self-replication process makes them a great analogue for real life on Earth.
Adami has bigger plans for Avida, however.
Life’s universal theme
He’s looking for a trait that all life forms across the universe would possess — a universal theme of sorts that would go beyond the chemicals they’re made of.
If this universal theme exists and we knew how to identify and test for it, we could quickly identify life on other moons or planets, even if that life has a completely different chemistry compared to life on Earth.
Adami thinks he’s pretty close to finding this theme.
“There are in fact things that are universal to all forms of life, everywhere, and what that is, is information,” Adami said. “Basically information is that which allows you to make predictions. And all living systems have to do that.”
This information is stored inside of every organism’s genome —
the complete set of their genes. A good way to picture this information is to think of it as individual pieces, or bits, like the bits that computers use to communicate.
A single strand of human DNA, for example, likely contains hundreds of millions of these information “bits,” says Adami. And the way organisms evolve, he says, depends on how these so-called bits replicate and mutate over time.
In a lecture, famed astrophysicist Stephen Hawking talks about how the information in our DNA has “probably changed by only a few million bits” over the last several million years as we evolved from apes.
Of course, Hawking is an astrophysicist and not an evolutionary biologist, so this theory should be taken with a grain of salt. But he’s not the only one to suggest the evolution is driven by changes in our genome’s information bits.
The big question
The big question is how to distinguish between the information stored in molecules in living organisms and the ones stored in non-living objects.
One way of doing this is by looking for patterns, says Adami.
Unlike living things, which generate specific patterns as they self-replicate and reproduce (like how sequences in our DNA repeat themselves), things that are not living will have only random bits of information that never repeat at regular frequencies.
So the task is this: Find the repeated sequences.
Unfortunately, that’s easier said than done.
The best way to do it, he says, is to take a look at the chemicals inside the soils of other moons and planets in our solar system. No one has begun doing this yet. There are no instruments on board NASA’s Mars rovers that use Adami’s method and we have no working rovers on other planets or moons at this time.
A fourth domain of life?
Although discovering alien life within the soils of other worlds might be far off, scientists on Earth are aiming to hunt down life forms never-before discovered. Their approach is o
ne of the most promising experiments that could ultimately help us find extraterrestrials
In November, 2014, a team of researchers at the Joint Genome Institute proposed an experiment that would search for a fourth domain of life here on Earth.
Right now there are only three known domains of life. The three domains are archaea, bacteria, and eukaryote where each domain has a specific sequence in their RNA gene structure that distinguishes them from the other two groups.
But the team at JGT suspects that there might be a fourth domain with an RNA sequence completely unlike anything seen before.
“We are poised, armed with a new toolkit of powerful genomic technologies to generate and mine the increasingly large data sets to discover new life that may be strikingly different from those that we cataloged thus far,” said JGI director Eddy Rubin in a statement.
To do this, the team wants to take a look the genes of cells in tiny life forms that lived more than 2.3 billion years ago, at a time when Earth’s atmosphere had far less oxygen than it does today. The low-oxygen conditions at that time might have spurred a genetically-unique life form that could even resemble life forms on other worlds that have little oxygen in their atmosphere, like Mars. This coveted new life form is biology’s version of “dark matter“.
Whether it’s on Earth or another world, there’s certain to be exciting new advances in the search for new life.
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