These Rogue Worlds Upend the Theory of How Planets Form

“We know from direct imaging searches of young stars that very few stars have giant planets in [wide] orbits,” Bate said. “It is difficult to accept that there were many large planetary systems in Orion to disrupt.”

Rogue Objects Abound

At this point, many researchers suspect there’s more than one way to make these strange in-between objects. For instance, with some fiddling, theorists might find that supernova shock waves can compress smaller gas clouds and help them to collapse into pairs of tiny stars more readily than expected. And Wang’s simulations have shown that booting giant planets in pairs is, at least in some cases, theoretically unavoidable.

While many questions remain, the multitude of free-floating worlds discovered in the past two years has taught researchers two things. First, they form quickly—over millions of years, rather than billions. In Orion, gas clouds have collapsed and planets have formed, and some, perhaps, have even been dragged into the abyss by passing stars, all during the time in which modern humans were evolving on Earth.

Sean Raymond developed simulations that show how large planets can punt their siblings into space, thus providing one potential explanation for the free-floating worlds.

Photograph: Laurence Honnorat

“Forming a planet in 1 million years is hard with current models,” van der Marel said. “This [discovery] would add another piece to that puzzle.”

Second, there are a ton of untethered worlds out there. And the heavy gas giants are the hardest to evict from their systems, much as a bowling ball would be the hardest object to knock off a billiard table. This observation suggests that for every Jupiter spotted, numerous free-floating Neptunes and Earths are going unnoticed.

We likely live in a galaxy teeming with banished worlds of all sizes.

Now, nearly half a millennium after Galileo marveled at the myriad pinpricks of light—moons, planets, and stars—in Earth’s skies, his successors are getting acquainted with the brightest tip of the iceberg of darker objects adrift between them. The tiny stars, the starless worlds, invisible asteroids, alien comets, and more.

“We know there’s a whole bunch of crap between stars,” Raymond said. This kind of research is “opening a window on all of that, not just free-floating planets but free-floating stuff in general.”

Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.


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