Ultraviolet radiation present on the surface of alien planets should not be a limitation for the development of life, concludes a study on the four closest potentially habitable planets to Earth.
Not long ago, we discovered that the Proxima Centauri Star System is orbited by a very peculiar and interesting planet.
Dubbed Proxima-b, the alien world was the subject of numerous studies, some of which concluded it may host the perfect incidents for life to develop on its surface.
The more we studied the not-so-distant exoplanet, the more we understood about its potential. That was until hopes for life were dashed by the high levels of radiation bombarding those worlds.
According to astronomers, Proxima-b, located a ‘mere’ 4.24 light years away is bombarded with 250 times more X-ray radiation than Earth, which means that its surface is most likely covered in hazardous, ultraviolet radiation.
So, how could life survive this extreme bombardment?
According to Cornell astronomers, it’s not that big of a deal, and life has already survived this sort of dangerous radiation, and the ultimate evidence is the human race.
According to a new paper titled “Lessons From Early Earth: UV Surface Radiation Should Not Limit the Habitability of Active M Star Systems,” published by Lisa Kaltenegger and Jack O’Malley-James in the Monthly Notices of the Royal Astronomical Society, “all life on Earth today evolved from creatures that thrived during an even greater UV radiation assault than Proxima-b and other nearby exoplanets currently endure.”
Evidence of that is our ancient Earth. Some four billion years ago, the planet was a chaotic, irradiated and hot mess, as Cornell scientists put it.
Despite this, life survived, complex lifeforms evolved on Earth.
And this is exactly what could be happening on this very moment on some of the nearest exoplanets to Earth, reveals Kaltenegger and O’Malley-James.
All of these planets have something in common, they orbit around a red dwarf star which, unlike our sun, flares frequently, which means the surface of these planets are constantly bombarded in high-energy UV radiation.
We don’t’ know what condition exists on these alien worlds, but we do know that solar flares can damage biological life, and erode away planetary atmospheres. This means that the surface of the planet, as well as any potential lifeforms, are exposed to a higher level of radiation, which cause biological molecules like nucleic acids to mutate or even shut down.
To understand more about how radiation affects life, the researchers created several simulated atmospheric compositions, ranging from ones we have on Earth today, to more eroded and anoxic planetary atmospheres.
They discovered that as atmospheres became thinner, more high-energy UV radiation bombarded the surface.
Scientists compared the models to Earth’s geological history, and conditions that existed on the planet some 4 billion years ago.
Although the modeled planets were bombarded with higher UV radiation than that emitted by our own sun today, this is significantly lower than what Earth received 3.9 billion years ago, Cornell University scientists discovered.
“Given that the early Earth was inhabited,” the researchers wrote, “we show that UV radiation should not be a limiting factor for the habitability of planets orbiting M stars. Our closest neighboring worlds remain intriguing targets for the search for life beyond our solar system.”
But what about exoplanets that orbit inactive M-class stars, whose radiation flux is relatively low? Does it mean that for life to evolve, it requires the high levels of radiation of early Earth?
To find out, researchers analyzed the mortality rates at different UV wavelengths of the extremophile Deinococcus radiodurans; an extremophilic bacterium, one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and is therefore known as a polyextremophile and has been listed as the world’s toughest bacterium in The Guinness Book Of World Records.
Experts note that not all wavelengths of ultraviolet radiation are equally damaging.
“A dosage of UV radiation at 360 [nanometers] would need to be three orders of magnitude higher than a dosage of radiation at 260 [nanometers] to produce similar mortality rates in a population of this organism,” revealed experts.
Organisms on Earth have been found to adapt and make use of a variety of survival strategies, including developing protective pigments, biofluorescence, and living under the soil, water or rock.
If organisms on Earth can do it and survive, chances are that the same techniques could be imitated by alien life located on some of the recently-analyzed exoplanets.
“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,” O’Malley-James said.
Kaltenegger added that “research demonstrates that in the quest for life on other worlds, our closest worlds are fascinating targets to explore.”