Life can thrive in a 100% hydrogen atmosphere, according to a new study. The finding could completely change our understanding of how (and where) life might exist in the universe.
For the study, a team of researchers led by Sara Seager, an astrophysicist and planetary scientist at the Massachusetts Institute of Technology (MIT), conducted experiments with the bacteria Escherichia coli, or E. Coli, and yeast. They put these species in a 100% hydrogen atmosphere. And, incredibly, the microbes survived, showing how life can live in such an extreme atmosphere. (For contrast, hydrogen makes up less than one part per million of Earth's atmosphere, which consists of mostly nitrogen.)
"I want to push astronomers to think more broadly about what kind of planets might be habitable," Seager told Space.com in an email. "Biologists, if they ever thought of hydrogen-rich atmospheres, would think it's fine for life to survive, because hydrogen is not known to be toxic to life" she said. However, she noted, astronomers "are not aware that life can survive in hydrogen-dominated atmospheres, so our work was to give a clear and concise experimental evidence that it is so."
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So, Seager explained, researchers might consider studying exoplanets — or planets outside the solar system — that they otherwise wouldn't target in the search for alien worlds that could potentially support life. Additionally, because hydrogen-heavy atmospheres are usually larger and more extended from their planet's surface, they could be easier to spot with some observing techniques, she added.
The microbes that Seager and her team studied in the lab grew more slowly in the 100% hydrogen atmosphere than they would in a "normal" Earth environment, Seager said. "A few times more slowly for E. Coli and a few hundred times more slowly for yeast," she said. However, she added that "this isn't too surprising, because without oxygen the microbes have to get all their food from fermentation, and that just doesn't yield as much energy."
While this experiment showed how life can survive in a pure hydrogen atmosphere, scientists don't expect to find exoplanets with atmospheres made up of 100% hydrogen. Still, they do expect to find some exoplanets with hydrogen-dominated atmospheres, Seager said.
Looking to the stars
These findings are especially important to the search for life because, although they haven't found them yet, astronomers think that there are likely large, rocky exoplanets with thin, hydrogen-rich atmospheres, Seager said.
"We don't know any planets like that — yet," Seager said. "Theory says they should exist … However, Jupiter, Saturn, Uranus, Neptune, giant exoplanets [and] mini Neptunes all have H2 [Hydrogen] and He [Helium] dominated atmospheres — though no one thinks life is there."
Going forward, knowing that life can survive in hydrogen, researchers could expand their observations of far-off exoplanets and their atmospheres. They could expand their gaze to look for such planets they might have otherwise overlooked while making observations with existing technology. Additionally, when tools like NASA's James Webb Space Telescope launch to space (the space telescope is currently set to launch in March 2021), they will be able to get even better observations.
This work was published today (May 4) in the journal Nature Astronomy.
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"Going forward, knowing that life can survive in hydrogen, researchers could expand their observations of far-off exoplanets and their atmospheres."
Before going too far forward, it might be advisable to understand if life could even arise in a hydrogen-rich environment. Placing life from a 20% oxygen atmosphere (highly reactive) under hydrogen and watching them survive for any length of time is not very demonstrative.
Abiogenesis as occurred on earth, with regard to the atmosphere, must have had certain limits on a bio-essential chemistry. What those limits are is certainly unknown, but extremes can be ruled out, Any limits would likely include a range of acceptable atomic and molecular components in the exo-atmospheres where life might arise abiotically.
Assuming hydrogen-rich atmospheres are conducive to life (reasonable probability), its mere presence in any exoplanet does not mean the conditions could or could not give rise to life. There are other elements and compounds which could "poison" the atmosphere, possibly at levels which would escape detection. One should obtain as much information as to composition of any exo-atmosphere to reasonably predict a probability of abiogenesis and the presence of life.
Sulfuric acid, such as observed in the atmosphere of Venus, would be only one of many obstacles.
For some, a more appropriate question might be:
"Have we found any evidence for life having existed on Mars?"
That one has a very clear answer: No
Question: How much evidence is there that Abiogenesis occurred (or not) on earth?
Almost no self-respecting scientist would tell you that a magic wand made it happen. And seeding without space ships is highly improbable. High probability mechanisms often over-rule low probability alternatives simply by deductive reasoning. A clear understanding of the science involved is critical to this understanding.
I'm open to thoughts.
Life arising from an alien source (off-earth) only puts the origin of life somewhere else. It has to start in some way, either by natural processes (i.e. "abiogenesis" - from lifeless chemicals), or by supernatural means (i.e. "the magic wand" - choose anything you like - no proofs required!).
For the term "spontaneous", one definition is of a rapid event, occurring quickly - almost immediately some might say. This would be highly unlikely for the process of abiogenesis. It is simply not a rational concept based on life's extreme complexity. Such spontaneity falls under "supernatural means".
But "spontaneous" has other meanings, and one of these is most appropriate for abiogenesis: "occurring without apparent external cause" - that is, a natural event occurring on-earth (a magic wand need not apply).
For those of us who are fans of real science and what it all means, abiogenesis* is the most logical and rational approach because it relies on well defined chemical interactions, many found in standard chemistry books, particularly organic chemistry. Many of the reactions and interactions that occur in life are already known to occur in the absence of life. This clearly provides a solid, logical foundation for abiogenesis.
To be sure, laboratory experiments demonstrate that some of the fundamental building blocks of life, such as amino acids, can be produced by a simple mixture of chemicals subjected to energetic sources (lightning, radiation, etc.). Such experiments provide the best approach to establishing an origin of life, assuming logic is the primary driver of rationale and reasoning on this subject.
The devil, as it were, is in the details of how all this complexity arose. But that it arose without outside interference is accepted by almost everyone who works in the sciences - for obvious reasons.
An old, alternate concept of how life arose is known as "Spontaneous Generation". This notion suggested that all life simply popped up everywhere, and anywhere. Like magic! You just had to "catch it in the act" to prove this notion was correct. Such origins of life were largely disproven by Pasteur and Tyndall in the 1800s. Even a below-average grasp of logic dictates that Spontaneous Generation as the origin of life is simply not possible.
To be sure, the old and dead concept of Spontaneous Generation is in NO WAY associated with abiogenesis, and anyone suggesting otherwise is sadly mistaken.