Another month, another study telling us a planet is or isn’t habitable. There have been a lot. Like, a lot a lot a lot a lot.
Previous studies have focused on the red dwarf planets around TRAPPIST-1. This one takes a (slightly) different approach in looking at Proxima b, which is the closest exoplanet to Earth.
Published in The Astrophysical Journal Letters and led by NASA’s Goddard Space Flight Center, it suggests that despite being close (4.2 light-years away), Proxima b may not be very good for life at all.
Specifically, the study says that the planet probably couldn’t support an Earth-like atmosphere, owing to its proximity to its host red dwarf star, Proxima Centauri. Simulating our own planet around that star, the study suggests our atmosphere would be blown away by the star’s activity.
“We decided to take the only habitable planet we know of so far – Earth – and put it where Proxima b is,” said Katherine Garcia-Sage, lead author of the study, in a statement.
The rate of atmospheric loss at Proxima b, which orbits in 11.2 Earth days, was found to be 10,000 times faster than that at Earth around the Sun. Without an atmosphere, it wouldn’t be able to support liquid water on its surface, despite being in the star’s habitable zone.
Red dwarfs have come under such scrutiny lately because they are the most numerous stars in our galaxy. Being dimmer than stars like our Sun, it is also easier to study planets in orbit around them. TRAPPIST-1, Proxima b, and others also have the added benefit of being pretty close to Earth.
Proxima Centauri and other red dwarfs, though, are active. This means they are continually firing out flares of radiation, and because their planets orbit so close, they are right in the firing line. The amount of ultraviolet radiation hitting Proxima b is hundreds of times greater than Earth.
“This study looks at an under-appreciated aspect of habitability, which is atmospheric loss in the context of stellar physics,” said Shawn Domagal-Goldman, a Goddard space scientist not involved in the study, in the statement. “Planets have lots of different interacting systems, and it’s important to make sure we include these interactions in our models.”
In a worst-case scenario, with the highest temperatures and an open magnetic field, Proxima b would lose its atmosphere in 100 million years. That’s not great, as the planet is 4 billion years old. In a best-case scenario, the atmosphere could last 2 billion years.
Yes, this is pretty bad news for our search for life. This not only makes life on Proxima b implausible, but questions that on other red dwarf planets too. Here’s hoping for a counter-study in the future to give us a bit of hope.