Not too far away, a small star recently unleashed an unexpectedly intense series of flares. The series kicked off with a behemoth eruption that was 10,000 times more powerful than anything ever recorded from the sun. For a few brief moments, the star blazed many times brighter than normal.
Another half-dozen flares and two weeks later, the episode ended. But the explosive cluster had been hotter, more powerful, and longer-lasting than scientists had expected to see. It would definitely not be good news for any planets orbiting close to the tempestuous star.
The star is a young red dwarf that is only about one-third the sun’s mass. It’s part of a binary dwarf system called DG Canum Venaticorum (or DG CVn for short), located about 60 light-years away. Red dwarfs are the most plentiful type of star in the galaxy, outnumbering everyone else by about three to one. Small, cool, and remarkably long-lived, these stars are considered by many scientists to be excellent hosts for life-friendly planets.
But on April 23, you would not have wanted to be anywhere near this little star. Spinning 30 times faster than the sun, the star’s rapid rotation amplified a burgeoning distortion in its magnetic field. When the tension finally snapped, it launched the mega-flare into space. As observed by NASA’s Swift satellite, that initial explosion reached a temperature of about 200 million Celsius (more than 12 times hotter than the center of the sun). It released enough high-energy X-rays to briefly outshine the star itself — and its nearby friend — in all wavelengths of light.
If a comparable flare had erupted from the sun and been followed by a cloud of charged particles, Earth would be in a bit of trouble, says astronomer Rachel Osten of the Space Telescope Science Institute. Those particle storms that often accompany flares are called coronal mass ejections, and when they’re energetic enough, they can disrupt both ground- and space-based communication systems.
“In terms of our own space weather, it is the mass ejections and energetic particles that can do the most damage,” she says. “The effects [of this mega-flare] would be worse than the biggest space weather event we’ve experienced so far.” (Here’s a description of the massive 1859 eruption known as the Carrington Event.)
But in addition to messing with power grids, knocking out short-wave radio communication systems and disrupting the global positioning system, such a mega-flare would have a notable bright side: Spectacular auroras, observable down to very low latitudes instead of just around the poles.
Of course, this little star’s super-spasm was no threat to our home planet. But any planets in its life-friendly zone would have been in for a rough time. “It must surely have been catastrophic,” says astrophysicist Stephen Drake of NASA’s Goddard Space Flight Center.
Red dwarfs are cooler than the sun, so planets warm enough to have liquid water on their surfaces orbit nearer the star, at perhaps one-tenth the Earth-sun distance. Because of that, these planets are tidally locked in orbit and always have the same face pointed toward their star. In other words, one half of the planet is bathed in perpetual day, the other half blanketed by endless night.
A mega-flare of this size, followed by a coronal mass ejection, would not be a welcome occurrence for a planet snuggled close to DG CVn — especially not for the part of the planet staring at the star.
“Any ozone layer on the star-facing hemisphere would surely be destroyed, the upper atmosphere would be hit by this large pulse of radiation, and then, maybe several hours later, if the geometry lined up, the associated coronal mass ejection would crash into the planet’s magnetosphere, and likely completely collapse it to the planet’s lower atmosphere on the star-facing hemisphere,” Drake says. “I would imagine that this, if the planet supported life, would produce the kind of major extinction event that we see a number of examples of in the Earth’s history.”
Many astronomers are excited about the possibilities of finding habitable planets around red dwarf stars. In addition to being close to the star and relatively easy to spot, these planets also have the luxury of maturing into old, old, old age. Red dwarf stars are exceptionally long-lived, with lifespans calculated to be on the order of trillions of years, so any nearby extraterrestrial lifeforms theoretically have lots of time to evolve.
But one of the chief concerns raised when discussing habitable planets around red dwarfs is the stars’ propensity for violent stellar outbursts, which could deal deadly blows to any organisms struggling to gain a toehold on their home worlds.
Yet flares the size recorded earlier this year around DG CVn are rare, Drake says, and tend to occur when the stars are very young — as this star is. Scientists estimate DG CVn is only about 30 million years old, which makes it less than one percent of the solar system’s age. So, planets forming around it are still very young, and far from habitable at this point.
“Any planets it may have in its habitable zone are still completely inhospitable to life,” Drake says. “Their surfaces are likely still molten. It took life perhaps a billion years to eventually develop on the Earth, as you know, so DG CVn still has lots of time to become the host star of a planet with life.”