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A Swarm of Comets Around an Alien Star Hints at Our Solar System’s Youth

The comets fall in two groups — one older and one younger — and have to contend with the orbit of a gas giant

An artist's impression shows exocomets orbiting the star Beta Pictoris (ESO/L. Calçada)
smithsonian.com

The second brightest star in the Southern sky’s Pictor—the constellation also known as the Easel—is intriguing to astronomers. The star, called Beta Pictoris, is relatively young, just 23-million years old, and in the early stages of forging its planetary system out of gas and dust. 

But the most interesting thing about Beta Pictoris is how it can tell us about the wild and crazy days of our own solar system’s youth.

As researchers peer at this system, they can measure flickers of starlight as bodies pass between us and Beta Pictoris. The same concept has helped us find the thousands of alien planets we’ve catalogued thus far. This star, however, is surrounded by hundreds of comets. It also has at least one exoplanet, which resembles a larger, rapidly spinning Jupiter.

Comets in general are like balls of ice and dust that send their long tails pluming when they get close to a star. The many comets of Beta Pictoris can be grouped into two families. One group circles farther out and slower, reports Lee Billings for Scientific American. The other stays closer to the star and has a range of speeds. The findings were just published in the journal Nature. 

The outer group acutally seems to be streaming out more gas than the inner group — a somewhat unexpected finding given what we know about comets. But Billing explains:

According to the study’s lead author, Flavien Kiefer, an astronomer at the [Paris Institute of Astrophysics], the likely explanation is that the inner family consists of older comets that have nearly depleted their reservoirs of gas and dust, whereas the outer family is composed of fresher or bigger comets produced from the recent fragmentation of a larger parent body. Based on the orientations of their scattered, close-in orbits, the inner cometary family also appears to be trapped in an orbital resonance, herded around the star by the gravitational influence of a nearby massive planet—perhaps Beta Pictoris b, or maybe another world as yet unseen.

The resonance effect is very similar to the way Jupiter influences comets in our own solar system and occasionally sends one closer to the sun. 

"Our work shows that processes known to take place in the solar system also take place in young planetary systems," Kiefer told Space.com. "This reinforces the feeling that when looking to the Beta Pictoris and its environment, we are observing a somewhat younger version of our sun, when it was 10 million to 20 million years old and it just formed its planets."

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