After an interstellar asteroid shot past the sun, scientists realized that there’s probably a lot of itinerant rocks out there. Those stones are changing what we know about the birth of solar systems.
Quanta Magazine said:In 2017, a weirdly shaped rock with a strangely erratic orbit swept through the solar system, leaving as quickly as it arrived. Astronomers soon realized that it was not from around here. It punched through the planets’ orbital plane from the top down, like a dart thrown at the concentric rings of a dartboard, and it moved super fast, way too quickly to be caught in the sun’s gravity. It was also extremely dark and seemed oddly elongated, but because it was so speedy, many of its properties will remain forever mysterious.
But it turns out that the object, the first interstellar asteroid ever observed, was not unique. It may not even be all that rare. Astronomers are coming to realize that objects like it may pepper the galaxy, perhaps in such great numbers that they influence the formation of larger worlds, maybe even entire planetary systems — including our own.
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Last year, at a meeting in Switzerland about ‘Oumuamua, Michele Bannister and Susanne Pfalzner sat down together during a coffee break. Pfalzner, an astronomer at the Jülich Research Center in Germany, casually asked Bannister, an expert on planet formation, what would happen if some ‘Oumuamua-like object from interstellar space came through the disk surrounding a young star. “What is the effect of all these things in the disk?” she asked. “What does an interstellar object do if it gets into a protoplanetary disk?”
Bannister, who authored one of the early papers about ‘Oumuamua, thought about it for a minute. ‘Oumuamua is roughly 100 meters long — big enough to make a ripple in a roiling cloud of dust and gas. “We looked at each other, and we thought, ‘This has got to be important,’” Bannister said. The pair started sketching out ideas.
“The more I was looking at this, the more I couldn’t believe someone hadn’t already thought of this,” said Bannister, an astronomer at Queen’s University Belfast.
In a paper published in April in The Astrophysical Journal Letters, Bannister and Pfalzner argue that rocks like ‘Oumuamua might be catalysts for planet formation. There are probably uncountable billions of such objects sailing through the cosmos, they say. When one intersects with a billowing envelope of gas and dust surrounding a young star, it might cause turbulence and shear that stirs the gas, sculpting it into patterns that later form planets.
In addition, they argue that ‘Oumuamua-like items might move at the right speed to become permanent residents. Infant solar systems could catch great numbers of these interstellar travelers. In their new homes, these immigrants would begin to gather smaller pebbles and dust grains, growing into larger objects. In doing so, they would provide the building blocks for pebble accretion, a theory that explains how large objects can grow very quickly into planets.
“It’s not a huge amount of mass; it’s more their presence in the disk that would trigger it,” Pfalzner said. “It’s a seed stage. You can grow a huge tree, but it always starts from a tiny seed. It’s not the mass of the seed. It’s the potential, if you will.”
Some sort of seed is needed. Recent observations from telescopes such as the Atacama Large Millimeter/submillimeter Array are showing that planets form very rapidly around young stars. This seems odd, based on what astronomers know about planet formation, but it’s possible that interlopers are helping out, Bannister says.
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