Only a few years ago, astronomers heralded the discovery of a rocky world circling the sun's closest space neighbor, Proxima Centauri.
The star, just four light-years away, is known as a red dwarf, or M-type, and is quite different from Earth's own. Although the exoplanet, Proxima b, orbits extremely close — a year there is only 11 Earth-days — its star's relatively smaller size and lower temperature could mean this world has the right conditions for liquid water to pool on its surface.
But a new study may have dashed scientists' hopes that the alien world could support life. The star’s flares are much more violent than previously thought, the researchers say, potentially obliterating the planet’s air. Not having an atmosphere, which traps important gases like oxygen and water vapor, may render a planet uninhabitable, even if it were otherwise an Earth doppelganger.
"Our Sun’s activity doesn’t remove Earth’s atmosphere and instead causes beautiful auroras because we have a thick atmosphere and a strong magnetic field to protect our planet," said Meredith MacGregor of Johns Hopkins University in Baltimore, one of the authors, in a statement. "But Proxima Centauri’s flares are much more powerful."
The study relied on the Atacama Large Millimeter/submillimeter Array, or ALMA, a telescope in Chile that can detect light at radio and millimeter wavelengths. During 50 hours of observations, the team saw 463 flares, which occur when a star's magnetic field tangles, compresses, and causes an explosion. Such a blast releases a torrent of radiation.
Some of the flares only lasted a handful of seconds, but the strongest ones were so powerful that they could destroy a planet's atmosphere over time, according to the research. The paper was published in The Astrophysical Journal.
The study suggests Proxima Centauri's flares are much more frequent and extreme, likely because it is fully convective. That means unlike the sun, which has layers that behave differently, Proxima Centauri's entire structure moves like a boiling cauldron of water. The result is a magnetic field that is always jumbling and snapping, releasing enormous bursts of energy.
If the researchers had only studied the star's activity in visible light wavelengths, they wouldn't have gotten a complete picture of the high-energy particles Proxima Centauri releases, MacGregor said.
"When we see the flares with ALMA, what we’re seeing is the electromagnetic radiation — the light in various wavelengths," she said in a statement. "But looking deeper, this radio wavelength flaring is also giving us a way to trace the properties of those particles."
Though Proxima b may be nothing more than an irradiated rock, scientists are continuing to look at rocky worlds outside the solar system, specifically those closely orbiting small red stars, to determine whether they can hold onto atmospheres. Despite red dwarfs being the most common stars in the Milky Way, nobody knows whether these planets can host air.
A massive James Webb Space Telescope campaign will home in on a dozen nearby-ish planets over the next two years to try to answer that question. The program, first reported by Mashable, budgets about 500 hours of observations on Webb, along with about 250 orbits of ultraviolet observations with the Hubble Space Telescope, to help characterize the host stars' activity.
Néstor Espinoza, an astronomer heading up the campaign's implementation, said it's a high-risk, high-reward program.
"If you found out that none of them have atmospheres, that would be pretty sad, but also pretty interesting," he told Mashable last year. "It would mean that our planetary system is actually really, really special."
