UV-drenched exoplanets might still host life after all
Whether or not there's life beyond Earth is one of the most profound questions we can ask, and nearby exoplanets are among the best places to start looking. Unfortunately, some of the most likely candidates are bathed in apparently-lethal levels of radiation – but a new study from Cornell University says that might not be a problem. Case in point: Earth.
Red dwarf stars are often considered a good start in the search for life – they're the most common type of stars in the Universe, and are relatively cool and small compared to the Sun. The problem is, that means planets need to tuck up closer to the star to stay warm enough for liquid water to pool on the surface. And being that close means they are subjected to intense ultraviolet and X-ray radiation, particularly during regular solar flares, which would be enough to kill most life on Earth today.
This has led many scientists to conclude that planets orbiting red dwarfs aren't as habitable as they once seemed. But the Cornell study took a closer look, by comparing the possible radiation levels these worlds receive with those our home planet has historically been exposed to.
The researchers focused on the four closest exoplanets to Earth that have been deemed potentially habitable: Proxima-b, TRAPPIST-1e, Ross-128b and LHS-1140b. Although we don't know the exact makeup of the atmospheres of these planets, the team modeled various compositions that could be possible, ranging from modern Earth-like structures to those with very thin atmospheres, and some without the protective ozone layer.
The team modeled how much UV reached the surface of the planets with these different atmospheres. As expected, the researchers found that those with thinner atmospheres and lower ozone levels received higher levels of UV radiation. But importantly, while that was more than the Earth currently receives, it was significantly lower than Earth levels of 3.9 billion years ago.
And since life had already taken hold by that point in the history of our planet, there's a chance that it could do the same elsewhere. Of course, that doesn't guarantee that life exists on Proxima-b or TRAPPIST-1e – it just means we can't rule it out, and should pay closer attention to these worlds.
"The history of life on Earth provides us with a wealth of information about how biology can overcome the challenges of environments we would think of as hostile," says Jack O'Malley-James, co-author of the study.
The research was published in the journal Monthly Notices of the Royal Astronomical Society. The team discusses the findings in the video below.
Source: Cornell University