Earth-sized planet Proxima b unlikely to host life

The nearby alien planet Proxima b is not a great candidate to host life as we know it, a new study suggests. Further, the study claims that the planet is exposed to frequent stellar eruptions despite being present in the "habitable zone" of its host star.

And because Proxima B lies within the habitable zone of its own star system, many scientists wondered whether crucial, life-sustaining liquid water could exist in it.

For the objective of their study, the researchers focused on red dwarfs, which are the most common and the longest-lived stars in the universe, and are, therefore, most likely to have planets locked in orbit around them.

Sad news for fans of Proxima B: a new NASA study suggests exoplanets in what were considered red dwarf habitable zones may not be able to support life after all.

Smaller cooler stars, like red dwarfs, have always been considered possible candidates for habitability as larger stars produce more heat and light. Similarly, the habitable zone of a cooler star must be located closer to it.

In the past, scientists typically considered the conditions of parent stars in a star system to determine whether a planet was livable. However, a new study by NASA suggests that stellar eruptions could also play a part in defining and determining the habitable zone of a star.

Vladimir Airapetian, a solar scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland and the lead author of the paper said "If we want to find an exoplanet that can develop and sustain life, we must figure out which stars make the best parents".

Such effects are particularly pronounced for exoplanets orbiting red dwarfs, which are often prime targets for potentially habitable exoplanets because they are the coolest, smallest and most numerous stars in the universe.

Along with light and heat, however, stars also emit ultraviolet and X-ray radiation, as well as stellar eruptions such as coronal mass ejections and flares.

"The stronger the ion escape effect becomes", he added.

When high-energy X-ray and extreme UV emissions from these flares hit a planet's atmosphere, they break molecules into atoms then ionize atmospheric gases, which knocks electrons free of the atoms and forms ions.

"To see how this effect scales when you get more high-energy input like you'd see from young stars, we developed a model".

The team's model estimates that young red dwarf stars generate enough high-energy radiation to allow elements such as oxygen and nitrogen, which are heavier then hydrogen (the lightest element), to escape a planet's atmosphere.

"We know oxygen ion escape happens on Earth at a smaller scale since the sun exhibits only a fraction of the activity of younger stars", said Alex Glocer, a Goddard astrophysicist. Based on assumptions about Proxima b's size and composition, its oxygen will be gone in about 10 million years.

Scientists say that, taking into account the star's age and proximity to the planet, Proxima b could be struck by X-ray and extreme ultraviolet radiation from stellar superflares roughly every two hours. Additionally, intense magnetic activity and stellar wind? the continuous flow of charged particles from a star? exacerbate the harsh space weather conditions.

Scientists say it is also important to factor in the age of a star and understand how all these aspects balance out.

  • Carolyn Briggs