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Last Saturday, a point of light twinkling in the shadows behind Jupiter erupted. And then it continued to erupt, with two more violent jets of material shooting into space on Sunday, followed by a fourth climax on Monday. As it raged and flared up, it became 250 times brighter than usual, like a lit match turning into a bonfire.
It is not a distant stormy star, nor a effervescent world covered with erupting volcanoes. It is comet 29P. And it delivered the performance of a lifetime that anyone with a sufficiently powerful backyard telescope could see.
To the knowledge of astronomers, this is the first time that this comet has had four eruptions in close proximity.
“Some call it a super explosion,” said Maria Womack, an astrophysicist at the National Science Foundation. “It takes an immense amount of energy.”
What causes the tumultuous cascade of this comet?
“We don’t know,” Dr Womack said. “And that’s what makes it so interesting.”
Comets are icy remnants of the anarchic birth of the solar system that are sometimes drawn by forces of gravity to the sun. Each comet is new in its own way. But comet 29P / Schwassmann-Wachmann – or 29P – is “strange in many ways,” said Kacper Wierzchoś, an astronomer at the University of Arizona.
Unlike most comets, it does not dive dramatically toward the sun before returning to the solar system’s outermost border. Instead, this 37-mile-wide ball of ice circles the sun in the space between Jupiter and Saturn – making it a type of object known as a centaur – in a bizarre, near-circular orbit. , touring the world every 14.6 years.
Despite being 560 million kilometers from the sun, the 29P is in a state of near-constant fury, frequently throwing gas and dust into the enveloping darkness. It is “always active and never goes out,” said Dr Womack.
This hyperactivity may be the result of its preponderance of carbon monoxide – a volatile gas – which needs only a hint of sunlight to heat up considerably and degas in space in large volumes. These flares briefly illuminate the comet’s atmosphere, or coma, filling it with dust reflecting sunlight.
There are at least seven bouts of enlightenment per year. “No other known comet in the solar system explodes with such frequency and intensity,” said Dr Wierzchoś.
But this exhibitionist comet outdid itself last week with its four consecutive explosions. Amateur and professional astronomers around the world quickly noticed that “its brightness was increasing in leaps,” said Richard Miles, director of the Asteroids and Distant Planets section of the British Astronomical Association.
The cause of this comet apparition, however, remains unknown.
The problem is, “we don’t know what causes 29P flares” on a regular basis, Dr Womack said. Maybe they’re triggered by the explosive vaporization of some of the comet’s chemistry. But Dr. Wierzchoś’s work has revealed that you can get a very dusty rash without a carbon monoxide explosion.
These eruptions could be the result of cryovolcanism, said Dr Miles. Sunlight warms and softens parts of the surface, beneath which lies subterranean slush of exotic ice – a cryomagma. When the comet’s weakened crust breaks, its cryomagma could be exposed to the vacuum of space. Its dissolved carbon monoxide would then burst out vigorously, propelling the cryomagma into cosmic expanse like champagne from a shaken bottle that was quickly uncorked.
Historically, more explosions happen after 29P got closest to the sun, that was in 2019. But why this super explosion now?
Maybe there was a gargantuan landslide, or a large chunk of 29P ruptured. “Who knows,” said Dr Wierzchoś.
Whatever the cause of this celestial spectacle, 29P remains “a rare and ever-open natural laboratory for studying the composition and behavior of primitive icy objects in the solar system,” said Dr Womack. Although it has been nearly a century since its discovery, the last quartet of record-breaking comet eruptions shows why many astronomers enjoy studying these ostentatious objects.
“They will surprise you,” said Dr Womack.
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