In the next space mission to Venus, scientists may use a new theory to test for extraterrestrial life.
According to Scientific American, this new theory “suggests that searches for molecular complexity could uncover convincing evidence of extraterrestrial life—and do so soon.”
At one time, our neighbor Venus was similar to Earth, only to become hostile to all life, or so it seems.
the Building Blocks of Life
Recently, scientists found a simple chemical signature that suggested possible life on Venus. Like other such findings, it’s ambiguous if life is truly there.
However, the new “assembly theory” would instead focus on finding more conclusive evidence by focusing on complex molecules, the building blocks of biology. Particularly when found in abundance, such organized molecules could indicate extraterrestrial life.
“[Assembly theory] is based on the idea that any form of biology anywhere in the universe will encode life’s information in complex assemblages of molecules that are measurably distinct from lifeless matter,” writes Natalie Elliot.
How Do You Define Life? Assembly Theory
To locate extraterrestrial life, one first has to define what life is.
In 1994 NASA defined life like this:
“Life is a self-sustaining chemical system capable of Darwinian evolution.”
However, it’s not practical for astrobiologists to test for “evolution” using current instruments. With assembly theory, they have a general way to recognize possible extraterrestrial life, both in the lab and in space.
The Mass Assembly Index
As part of the study, the scientists ranked 2.5 million known molecules. Each molecule received a mass assembly number (MA) assigned using algorithms. On the low end, the simplest molecule received a 1, indicating a lower chance for life or a biosignature.
At the high end, complex molecules receiving an MA of 15 or higher would “almost always be made by life,” at least on Earth. On other planets, the threshold may be considerably different.
Therefore, finding an MA 15 molecule on a planet like Venus would be exciting, another possible sign of life, but not necessarily 100% proof.
Possible signatures of Life
Recently, scientists discovered a smelly, flammable gas called phosphine in Venus’ atmosphere. As far as scientists know, phosphine can only be made by life processes, at least on rocky planets like Venus and Earth. Here, anaerobic bacteria in low-oxygen environments (including inside the gut of animals) produce the noxious gas.
According to National Geographic:
“Put simply, phosphine shouldn’t be in the Venusian atmosphere. It’s extremely hard to make, and the chemistry in the clouds should destroy the molecule before it can accumulate to the observed amounts.”
Nevertheless, the scientists caution they need to verify the finding.
“But if phosphine really is floating through the Venusian cloud deck, its presence suggests one of two intriguing possibilities: that alien life-forms are deftly linking together phosphorus and hydrogen atoms, or that some completely unanticipated chemistry is crafting phosphine in the absence of life.”
Other scientists challenge the idea of life on Venus, saying the phosphine may have originated from a “strange-but-lifeless form of Venusian volcanism,” if it’s there at all. A new study added evidence there is active volcanic activity on Venus.
Test on Venus
Using assembly theory, scientists can look in a new way, and it may be the best place to start.
“This is a real environment,” chemist Steven Benner says, “one soon to be visited in a space mission again. If Venusian life exists in the clouds above Venus, it would need to follow a chemical logic very much different from the logic that is followed by life on Earth.” This, Benner says, arguably makes Venus the best site for a near-term test of the molecular-complexity metric.”
Upcoming Missions to Venus
In June, NASA announced two new missions to the “lost habitable” world of Venus by 2030. Davinci+ (a shortening of Deep Atmosphere of Venus Investigations of Noble Gases, Chemistry and Imaging) will measure the planet’s atmospheric chemistry.
“This would be the first U.S.-led mission to Venus’ atmosphere since 1978, and the results from Davinci+ could reshape our understanding of terrestrial planet formation in our solar system and beyond,” NASA stated.
Then, the Veritas mission will map the Venusian topography and rock type using detailed infrared observations.
Interestingly, NASA scientist Justin Filiberto says he doesn’t think “anyone would be surprised that, when we got to Venus, we’d find evidence of volcanic activity.”
Even so, he suggests the missions may require rewriting the textbooks.
“I think we’re going to be writing brand new textbooks about Venus once all of these missions get there,” says Filiberto. “It’s going to change how we think about planetary evolution.”
If scientists apply assembly theory to examine Venusian molecules, perhaps the textbooks may need rewriting once more?