We are trying to change the way people think about a livable planet. Sara Seager, an exoplanet astronomer at the Massachusetts Institute of Technology, said. Water and oxygen are the conditions for life to live, and have long been one of the basis for astronomers to judge the existence of life on exoplanets. But recently, a team of researchers from MIT’s Earth’s Department of Atmospheric and Planetary Systems, Physics, Aerospace, and Chemistry found that some microbes can survive and thrive in a 100% pure hydrogen environment!
On May 4, 2020 local time, the team published a paper entitled Laboratory studies on the viage of life in H2-dominant exoplanet atmospheres (laboratory research on the viability of life in the atmosphere of hydrogen-based exoplanets) published online in the journal Nature Astronomy.
The atmosphere of a planet or hydrogen-based
Historically, astronomers tended to believe that there were other planets outside the solar system, until the 1990s, when humans finally confirmed the existence of exoplanets for the first time.
NASA Spitzer Space Telescope’s first direct observation of exoplanets
Since then, one of the focuses of astronomers’ research on exoplanets has been to explore the existence of life in exoplanets.
To explore the existence of life on exoplanets, it is important to analyze the composition of their atmospheres.
The rocky exoplanets are made up of iron-rich primitive materials, such as spherical meteorites, and water ice. The team, then, believes that during planetary formation, water and iron react to produce hydrogen, releasing it into the atmosphere, and that it is not impossible.
In chemistry classes, we’ve all learned that hydrogen is the least dense gas known in the world — at 1 standard atmospheric pressure and 0 degrees C, the density of hydrogen is 0.089g/L, and its density is only 1/14 of the density of air. It is also because of density that the hydrogen content in Earth’s early atmosphere is very small, 1,000 times less than it was 9 billion years ago. Today, the hydrogen produced on Earth is mainly consumed by microorganisms, oxidized in the atmosphere or disappeared into space.
Thus, in theory, a planet’s atmosphere, which is dominated by hydrogen or made up of 100% hydrogen, can be up to 14 times thicker than Earth’s, making it easier for astronomers to detect and observe it.
So, if one day we actually detect such exoplanets, can we find life?
With this in mind, the team came up with a bold guess: life could exist in a hydrogen-led environment.
Microbes can survive and thrive in pure hydrogen.
With the hypothesis, the experiment began.
The team designed a system consisting of a 30 ml medium (a standard medium for E. coli and yeast cell culture growth medium) and a small boric acid bottle with a top space of 126 ml.
The team placed E. coli and yeast in bottles containing pure hydrogen, pure helium, and a mixture of 20% co2 and 80% nitrogen (100% H2, 100% He, 20% CO2 and 80% N2) and anaerobic tests (plus a bottle as a control, air).
The team placed the bottle in a incubator shaker at 28 degrees C, using precise oxygen sensors for continuous measurements to keep the gas concentration stable and the culture to remain oxygen-deficient.
At the same time, the turbidity of cell cultures is quickly assessed through continuous monitoring with special cameras, and the growth of cultures is assessed periodically. There are two main indicators – e. coli photodensity (OD, optical density) and yeast blood cell count.
The image above shows the light density of E. coli, indicating that high concentrations of pure hydrogen and other gases do not impair E. coli survival and cell division. The black, blue, red and green curves represent a mixture of air, pure helium, pure hydrogen, 20% CO2 and 80% nitrogen.
The image above shows a blood cell count of yeast, which also shows that high concentrations of pure hydrogen and other gases do not impair yeast survival and cell division. The black, blue, red, and green curves represent a mixture of air, pure helium, pure hydrogen, 20% CO2, and 80% nitrogen.
It is not difficult to see that the above-mentioned microorganisms in the air survival, reproduction of the best situation, but at the same time, they can also survive in the environment of 100% hydrogen, reproduction.
In addition, the team showed the spectral characteristics of e. coli-producing gases in the paper based on available data, with the photos absorbing the relationship between wavelength.
Among them, researchers are still unable to determine whether methane CH4 and phosphated hydrogen PH3 in the spectral feature map are produced by E. coli, and many other spectral features are difficult to distinguish.
In fact, the spectrum is also significant – many of these gases can be detectable biomarkers in the atmospheres of hydrogen-rich exoplanets, such as dimethyl sulfur ether C2H6S (DMS in the figure), which in some ways increases astronomers’ chances of detecting signs of life on exoplanets.
In response, NASA space biologist Giada Arney said:
E. coli is such a simple creature, but it produces incredible gases. Understanding what gases life can produce is the first step in determining possible biomarkers on exoplanets.
It can be seen that this study is of special significance for the exploration of life on exoplanets. But John Baross, an astrobiologist at the University of Washington, agrees:
It’s not enough to look for a hydrogen-rich atmosphere. Life needs other substances to survive, like the medium in a bottle in an experiment, such as liquid water that exchanges chemicals with the surface of a rock.
Adding hydrogen-rich planets to the exploration of extraterrestrial life is no doubt another way to go. Perhaps, jumping out of the inherent thinking, we can prove more quickly that the earth is not a lonely planet in the vast universe.