Hydrogen-breathing aliens may exist on planets quite different from Earth

This is the conclusion of researchers from MIT who succeeded in growing a bacterium (E-COLI) and maintained it in environments simulating a hydrogen atmosphere 

By: Jennifer Chu, MIT, May 6, 2020, Translation: Ziv Adaki

New research suggests that next-generation telescopes will first look for hydrogen-rich atmospheres, because hydrogen may be a real and easily detectable biological signature of the existence of life.

In the coming years, as powerful new telescopes become operational, astronomers will be able to point these super telescopes at planets near our solar system and peer into their atmospheres to analyze their composition and look for signs of extraterrestrial life. But imagine that in our search we will indeed meet in life, but we will not recognize them as such.

Astronomers, including Sarah Seeger, hope that we will manage to escape such a possibility. Seeger, professor of planetary sciences, physics, aeronautics and astronautics at the Massachusetts Institute of Technology, looks beyond the "earthly" view of life and casts a wider net of environments in which life might exist.

In an article published May 6, 2020 in the journal Nature Astronomy, Seger and her colleagues reported that in experiments they conducted in the laboratory they saw that organisms (microorganisms) could survive and thrive in atmospheres composed mainly of hydrogen - this environment is very different from that of the Earth, which is rich in nitrogen and oxygen.

Hydrogen is a much lighter gas than both nitrogen and oxygen, and a hydrogen-rich atmosphere is much wider than that of a terrestrial (rocky) planet. Therefore, it may be easier to locate and study it with powerful telescopes, compared to planets with denser atmospheres, such as Earth's.

Seeger's findings, which show that simple life forms might inhabit planets with hydrogen-rich atmospheres, suggest that when next-generation telescopes, such as NASA's James Webb Space Telescope, come into operation, astronomers will first want to look for signs of life on planets where Hydrogen is the main component.

"There are a variety of worlds that might have life on them, and we've shown that life that originated on Earth can survive in hydrogen-rich atmospheres," Seeger says. "We need to add these kinds of planets to our menu of possibilities when we think about life on other worlds and look for it." Seeger's partners in writing the article are Jingcheng Huang, Janusz Petkowski and Mihkel Pajusalu.

Evolving atmospheres

On the young earth, billions of years ago, the atmosphere was quite different from the air we breathe today. In its infancy, there was no oxygen on our planet, it consisted of a mixture of gases, including carbon dioxide, methane and very little hydrogen. Hydrogen gas may have remained in the atmosphere for billions of years, until the so-called "oxygen disaster" and the gradual accumulation of oxygen occurred. The little hydrogen that remains on the surface of the earth today is consumed by species of ancient creatures, including methanogens - creatures that live in extreme climates, for example, deep under the ice or in desert soil, they devour hydrogen and carbon dioxide to produce methane.

Scientists are constantly investigating the activity of methanogens, which are grown in laboratory conditions with eighty percent hydrogen. However, there are few studies that examine the tolerance of other organisms to a hydrogen-rich environment.

"We wanted to show that life survives and can evolve in a hydrogen-rich atmosphere," says Seeger.

Right space

The research team brought two types of creatures to the laboratory to test their ability to survive in an environment of 100 percent hydrogen. They chose the Escherichia coli bacterium and yeast, a more complex eukaryote, which has not yet been studied in environments where hydrogen is the main component.

These two creatures are common models that scientists have often studied and characterized, which helped the research team design their experiments and understand their results. Furthermore, sonic and yeast can survive with and without oxygen - another advantage for the researchers, who could prepare their experiments in the open air, before transferring the two types of organisms to a hydrogen-rich environment.

In the experiments, the researchers grew cultures of yeast and coliforms separately, then injected them into separate bottles, filling each bottle with "broth" or a rich medium that could be used as food for the organisms. Next, remove the oxygen-rich air from the bottles and fill the remaining space with 100 percent hydrogen gas. The bottles were then placed in the incubator, where they were gently and constantly shaken to encourage mixing between the organisms and the food substrate.

Every hour, a team member collected samples from each bottle and counted the live critters. The bottles were sampled for eighty hours. The results obtained show a classic multiplication curve: at the beginning of the experiment, the number of the cytrons increased rapidly, they fed on the substrate and populated the culture. Later, their number balanced out. The size of the population, still thriving, remained stable, new creatures replaced those who died.

Seeger admits that biologists were not surprised by the results. Remember, hydrogen is an inert gas, and as such it is not toxic. "We didn't fill the space with poison," explains Seeger. "But you have to see to believe, right? If no one has ever tested these organisms, and especially eukaryotes, in a hydrogen-rich environment, we must test it so that we can believe the results." In addition, Seeger clarifies that the purpose of the experiment was not to test whether these creatures can rely on hydrogen as an energy source, but to show that an atmosphere consisting of 100 percent hydrogen does not harm or kill certain life forms.

"I don't think it has occurred to astronomers that there might be life in a right-wing environment," says Seeger and hopes that her research will spark a conversation between astronomers and biologists, especially when the search for planets with life enters high gear.

A world from me

With the tools we have at this time, astronomers cannot make a real examination of the atmospheres of small terrestrial planets. The few nearby planets that astronomers have studied either lack atmospheres or are too small to detect with existing telescopes. And while scientists speculate that planets do cultivate hydrogen-rich atmospheres, no telescope operating today has the resolution needed to detect them.

However, if the next generation of stargazers are indeed able to locate such terrestrial worlds, where the atmosphere is mainly composed of hydrogen, the findings of Seeger's research indicate the possibility that life is developing in them.

As for the nature of a hydrogen-rich terrestrial planet, Seeger compares it to the highest peak on Earth, Mount Everest. Mountain climbers trying to qualify for the summit run out of air, due to the fact that the density of the entire atmosphere drops exponentially as you go higher. This is especially noticeable in a nitrogen and oxygen atmosphere like ours. If the athlete was climbing mountains to the top of Mount Everest in an atmosphere that is mainly hydrogen - a gas 14 times lighter than nitrogen - it could climb 14 times higher before the air ran out.

"It's a little complex to understand, but this light gas creates an extensive atmosphere," explains Seeger, "and the larger the atmosphere compared to the planet's solar background, the easier it is for the telescope to detect it."

If scientists get the chance to sample this type of hydrogen-rich planet, Seeger hypothesizes that its surface will be different from our Earth's, but not completely unfamiliar.

"We hypothesize that if we drill into the surface, there will certainly be hydrogen-rich minerals, and not oxygen-rich minerals, as well as oceans, because we estimate that liquids of this type are necessary for the existence of any type of life, and, apparently, we will be able to see blue skies," says Seeger.

"It is true that we did not think about the entire ecosystem, but such a world would not necessarily be completely different from ours."

• for the scientific article
• For information on the MIT website