The dancing lights of the aurora are entrancing, but they’re hardly unique to Earth. All the other planets in our solar system have auroras too, and now, for the first time, scientists have caught a glimpse of an aurora outside our Sun’s neighborhood—and it’s really flippin’ huge.
The aurora of LSR J1835+3259 (which, unfortunately, doesn’t have a catchier name) gives off at least 10,000 to 100,000 times more power than Jupiter’s. If you could stand on the object’s surface without getting crushed by its gravity, “you probably wouldn’t be able to see anything else in the sky because of this intensely dazzling, red aurora,” says Gregg Hallinan, one of the astronomers who discovered the aurora.
LSR J1835+3259 is suspected to be a brown dwarf—an old star that can no longer sustain hydrogen fusion in its core. It’s located about 20 light-years away. It’s about the same sized as Jupiter, but much heavier, weighing in at 50 to 80 Jupiter masses.
“You probably wouldn’t be able to see anything else in the sky because of this intensely dazzling, red aurora.”
About 15 years ago, scientists were surprised to find that brown dwarfs can emit radio waves—usually that sort of activity is left to the more youthful stars. Hallinan’s team found the radio waves were pulsing like the beam from a lighthouse—which they’ve also observed on Jupiter—and they suspected that an aurora might be the cause.
When charged particles from the sun crash into Jupiter’s magnetic field, it creates the solar system’s largest aurora. Jupiter’s magnetic field attracts the charged particles, which collide with molecules in the atmosphere, resulting in tiny explosions of color. And as those charged particles cascade through the magnetosphere, they also emit intense radio waves in pulses.
By watching it for four years, Hallinan’s team found that the brown dwarf’s radio pulses were more similar to Jupiter’s radio wave pulses than to the sun’s, which led the team to conclude that it’s an aurora that’s causing the pulses.
“The signal was consistent with the spectrum that you see when electrons hit the atmosphere, although it was so much brighter than anything we’ve ever seen,” says Hallinan.
The immense power that the aurora emits suggests that the brown dwarf’s magnetosphere is about 200 times the size of Jupiter’s. That’s pretty large, considering Jupiter’s magnetic field is bigger than the sun. You could line up about 430 Jupiters inside the brown dwarf’s magnetosphere.
The team isn’t sure what’s fueling the massive aurora. On most planets, the winds from the sun supply a stream of charged particles–but the brown dwarf doesn’t have a star, because it is one.
The mechanism behind Jupiter’s own gigantic aurora could provide some clues. Jupiter’s aurora is partly powered by the moon Io, which orbits close to the planet, erupting volcanic debris and plasma into Jupiter’s magnetosphere. Perhaps something similar is happening on the brown dwarf, says Hallinan.
“It may be like an Earth-sized planet sitting inside magnetic sphere of this brown dwarf, spewing stuff into its magnetosphere.”
The team suspects that 10 percent or more brown dwarfs may have auroras.
“Maybe having a magnetic field is a really important part of having life evolve on this planet.”
But using radio waves to find auroras is not just about tracking down a pretty phenomenon—it’s also a way to measure a magnetic field really easily, and in the search for Earth-like planets, that could be important.
Earth’s magnetic field protects us from the sun’s harsh radiation as well as damaging cosmic rays. “Maybe having a magnetic field is a really important part of having life evolve on this planet,” says Hallinan. “We want to find out if other planets have these same kinds of shields.”