Last Saturday, a shimmering speck of light erupted in the shadows behind Jupiter. Then it continued to explode, as two more violent jets of material blasted into space on Sunday, followed by a fourth shift on Monday. As it blazed and blazed, it became 250 times brighter than usual, like a lit match turning into flames.
This is not a stormy distant star, nor is it a sparkling world covered in exploding volcanoes. This is comet 29P. And it performed the age that anyone with a backyard telescope powerful enough could see.
And as far as astronomers are aware, this is the first time this comet has shown four closely spaced outbursts.
“Some describe this as a supernova,” said Maria Womack, an astrophysicist at the National Science Foundation. “This takes a tremendous amount of energy.”
What is causing the naughty waterfall of this comet?
“We don’t know,” Dr. Womack said. “And that’s what makes it so fun.”
Comets are icy remnants from the chaotic birth of the Solar System, sometimes yanked by gravitational forces toward the Sun. Each guilty is a novel in its own way. But comet 29P/Schwassmann-Wachmann — or 29P — is “strange on many levels,” said Kacper Wierzchoś, an astronomer at the University of Arizona.
Unlike most comets, it does not sink dramatically toward the Sun before blasting back to the outer limits of the Solar System. Instead, the 37-mile-wide ice ball orbits the sun in the space between Jupiter and Saturn—making it a type of object known as a centaur—in a strange, semi-circular orbit, completing one raft every 14.6 years.
Despite being 560 million miles from the sun, 29P is in a near-constant rage, often spewing gas and dust into the surrounding darkness. It’s “always active and never off,” said Dr. Womack.
This hyperactivity is probably the result of the majority of carbon monoxide – a volatile gas – which needs only a great deal of sunlight to heat it up dramatically and releases the gases into space in large quantities. These explosions briefly light up the comet’s atmosphere, or comas, by flooding it with sunlight-reflecting dust.
There are at least seven bouts of sunshine per year. “No other known comet in the solar system experiences explosions of such frequency and intensity,” Dr. Wirzköy said.
But this show-stopping comet outdone itself last week with its four consecutive outbursts. Richard Miles, director of the Asteroids and Far Planets division at the British Astronomical Society, said amateur and professional astronomers around the world quickly noticed their “increased brightness during leaps”.
However, the cause of these guilty festivals remains unknown.
The problem, Dr. Womack said, is that we “don’t know what’s driving the 29P eruptions” on a regular basis. They may be caused by the explosive evaporation of some of the comet’s chemistry. But work by Dr. Wierzchoś found that you can have a dust-rich eruption without the accompanying carbon monoxide explosion.
Dr. Miles said these eruptions could be the result of ice volcanoes. The sun’s rays heat and smooth parts of the surface, under which there is an underground mud of strange ice – cryomagma -. When a comet’s weak crust explodes, its cryomagma can be exposed to the vacuum of space. The carbon monoxide dissolved in it then explodes with force, propelling the cryomagma into the cosmic expanse like champagne gushing out of a shaken bottle that has quickly been unscrewed.
Historically, more eruptions occur after 29P made its closest approach to the sun, which was in 2019. But why this super eruption now?
Perhaps there was a massive landslide, or a large part of the 29P broke off. “Who knows,” said Dr. Wierzcho.
Whatever the reason for this sky show, said Dr. Womack, 29P remains “a rare and always open natural laboratory for studying the composition and behavior of primordial icy bodies in the Solar System.” Although nearly a century has passed since its discovery, the comet’s latest record-breaking quartet of record-breaking eruptions highlights why so many astronomers love to study these massive objects.
“They’ll surprise you,” said Dr. Womack.