The hotly anticipated next generation of ground and space-based telescopes could reveal the answer as to whether life exists elsewhere in the universe, by providing observations of rocky planets that we have never been able to see before. One such class of rocky planets, that if exist would definitely be found by these new telescopes, are those with hydrogen-dominated atmospheres.
Whilst Earth’s atmosphere is predominantly composed of the gases carbon dioxide and nitrogen, an atmosphere full of the lighter gas hydrogen would be easier to detect, as its lower density would enable it to extend much further than an Earth-like one. Although high abundances of hydrogen are not generally thought to be conducive to life, in anticipation of future surveillance, a team of researchers from Massachusetts Institute of Technology (MIT), USA, have explored whether life could survive on a planet with such an atmosphere.
To do so, a team led by Professor Sara Seager tested whether the single-celled microorganisms Escherichia coli (E. coli) and yeast could grow and reproduce in an environment of 100 percent molecular hydrogen (H2).
“Although H2 is not known to be toxic to life in either small or large quantities… microorganisms have not been shown to grow in pure 100 percent H2 atmospheres before,” the authors wrote in their article, published in Nature Astronomy.
In their lab-based experiment, the team discovered that both the bacteria E. coli (representative of prokaryote microorganisms) and the fungus yeast (representative of the more complex eukaryotic microorganisms) reproduced as normal, albeit at a lower rate than in air – 2 times and 2.5 times slower, respectively. The authors attribute this difference to the lack of oxygen in the test atmosphere.
Nonetheless, Seager told IFLScience that their findings "demonstrate to astronomers that hydrogen doesn’t kill or deter life’s survival and growth." In fact, the team also noted that many gases given off by microorganisms like E. coli could be detected in exoplanet atmospheres if built up in sizeable abundances, serving as possible a sign of life. Many of these gases are already proposed as potential “biosignature” gases, such as ammonia and nitrous oxide.
"The simple E. coli produces an astonishing range of gases, giving us hope that simple life elsewhere can produce gases that might be attributed to life," Seager said.
Seager and her colleagues' results suggest that life could still exist even in some of the more unlikely large rocky exoplanets. "We should open our minds to what kind of planets we consider habitable, to increase our chances of finding signs of life beyond Earth," Seagar remarked.
As the next generation of telescopes start to become functional in the next few years, their observations will be hotly anticipated.
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