No matter how tough we think life is, it continually outdoes expectations. Now a new study from MIT has found that E. coli and yeast can survive in an atmosphere made up of 100 percent hydrogen. And that could have fascinating implications for life on other planets. In the hunt for alien life, we’re mostly focusing on planets that are the most Earth-like, for obvious reasons. But in doing so we might be limiting ourselves a bit too much. Even without leaving home, microbes have been found living in the hottest and coldest places on Earth, soaring through the upper atmosphere and colonizing rocks half a mile below the seafloor. Tests have even shown some species are fine with the harsh conditions of space itself. But in spite of that, when it comes to exoplanets we’ve taken a relatively selfish view of habitability. We humans may not be comfortable in the frigid deserts of Mars or the methane lakes of Titan, but that could be some microbe’s idea of paradise. We just have to test it out. Exoplanets with atmospheres made up of mostly hydrogen have traditionally been written off as uninhabitable, but not much research has been conducted to check whether that is the case. So the MIT team investigated just that. The researchers exposed E. coli and yeast cultures to atmospheres of 100 percent hydrogen, and to their surprise, the microbes fared just fine. Their reproduction did slow down somewhat, but it didn’t stop them. For E. coli, the rate of reproduction dropped by about half, while the yeast was about 2.5 orders of magnitude slower. According to the team, this was most likely due to the lack of oxygen. This finding means that we may need to revise the criteria for what constitutes an inhabitable planet. Hydrogen-heavy Super-Earths, for example, may be a good place to start, and conveniently enough they may be easier to spot than other types. That’s because hydrogen atmospheres can swell further out from the surface than others. Better yet, the team also says that we may already be able to figure out whether any of these planets actually are home to alien life. E. coli and other bacteria are known to produce gases like ammonia, dimethylsulfide, nitrous oxide, and methane. Detecting these in atmospheres otherwise dominated by hydrogen could indicate that there’s something living there.