Our solar system may be surrounded by a halo of 10 million interstellar objects

Oumuamua shall not be as extraordinary as we thought.

As our solar system circles in its 230-million-year orbit around the outer edges of the Milky Way galaxy, it is occasionally passed by bits of cosmic jets that are discarded by other stars: stray comets, asteroids, and other bits of space rock that have been ejected from their original homes (completely Like our solar system He might have expelled an entire planet). Occasionally, these objects drift through our solar system, intriguing us and Some really wild speculation.

But our solar system may actually contain a swarm of interstellar objects trapped in its outskirts, according to a recent study by University of Edinburgh astronomer and statistician Jorge Benarubia, published in the journal Monthly Notices of the Royal Astronomical Society.

what’s new – Using a truly terrifying amount of mathematics, Benarobia modeled how the gravity of our sun and the Milky Way Galaxy’s gravity affects interstellar objects approaching our solar system.

Oumuamua was the first interstellar object in our solar system that astronomers have spotted, but it wasn’t nearly the first to arrive—and it won’t be the last.VICTOR HABBICK VISIONS / SCIENCE PHOTO LIBRARY / Science Photo Library / Getty Images

As a piece of interstellar rock, like Oumuamua, orbits the center of our galaxy, it passes near a star system, in which eight planets and a group of small bodies orbit a yellowish star. The Milky Way’s tidal pull slows the wayward asteroid enough that the Sun’s gravity can grab it and pull it in in a very brief orbital dance.

However, the newly captured interstellar visitor has not settled into a permanent, stable orbit. Instead, it will only last a few laps, or perhaps only part of a lap, before the Sun sends it back into interstellar space with more energy than it did before the encounter. It will end up in a higher and faster orbit around the center of the Milky Way, in other words.

“This is exactly the same principle we use to send ships into the outer solar system,” Benarobia says. inverse. The Cassini, New Horizons, and Voyager probes have all used similar maneuvers to enrich their distant destinations.

Essentially, the Milky Way’s gravity slows down the interstellar body enough for it to fall into the orbit of the Sun. and the sun provides the gravitational slingshot; When it pulls the asteroid back into its orbit, it causes the asteroid to speed up—until that speed is enough for the comet to escape again.

Because the sun is constantly picking up new interstellar objects and ejecting old ones, we keep a very constant number of them in the rocky halo around our solar system, Benarobia said. These briefly captured interstellar objects may make up a large portion of the Oort Cloud, the hypothetical cloud of icy bodies surrounding the farthest outskirts of our solar system. Some of them end up on paths that sometimes bring them inward like Earth’s orbit.

It is difficult to say how many interstellar objects are part of our solar system at any given moment. Astronomers aren’t sure exactly how many comets and other objects are in the Oort Cloud (estimates, based on the tiny number of comets close enough to Earth for us to see, range from hundreds of billions to trillions), let alone trillions. How many such objects were hand-delivered from other solar systems, briefly plucked from interstellar space.

“Even if these things exist, we don’t yet have the technology to detect them in large numbers,” Benarobia says. “We only see very rare cases like ‘Oumuamua and Borisov.” Based on the two or three interstellar objects astronomers have discovered so far, Benarobia says his model predicts there should be about 10 million of them in the halo of the errant space fleet surrounding our solar system. Perhaps a few hundred of them orbit close to the sun, like Neptune.

Here is the background – In late 2017, astronomers detected a space intruder in our solar system: a long, narrow slab of rock (between 100 and 1,000 meters long), moving on a path that suggested it was passing through our solar system, on its way to and from somewhere in interstellar space. . And in October 2019, Comet 2I/Borisov It has flown through our inner solar system on a trajectory that indicates it came from somewhere outside our cozy little interstellar neighborhood. Astronomers called Borisov a “rogue comet” and studied it with interest.

The presence of these objects reminds us that our solar system is not in an airtight bubble, isolated from the rest of the galaxy.

“I think my work probably tells us that there must be a lot more out there than people think,” Benarobia says.

This illustration shows, roughly, where the Oort Cloud should be in relation to the most common central part of our solar system, and how far outward the space debris cloud extends.Ron Miller/Stocktrek Images/Stocktrek Images/Getty Images

why does it matter – Beings like ‘Oumuamua and Borisov are compelling to think about simply because they are from in another place. However, they are scientifically interesting because they give us clues about the chemical composition of other planetary systems, as well as clues about how these systems formed and evolved. And if Peñarrubia is right, we have plenty of interstellar objects in our solar system, just waiting to be found and studied — if we can find them, that is.

“If you can detect a large group of trapped objects, we will get a lot of information about how many elements in the Milky Way are floating around, and what composition they come from in different solar systems,” Benarobia says. . “And if that is the case, what kind of properties those solar systems had in the past, and their age distribution, would be very interesting.”

But finding these things will be a challenge. They should be there, Peñarrubia Model says, but most of them are too far away to see even with the most advanced telescopes — for now.

What’s Next – until the James Webb Space Telescope Most of the Oort Cloud cannot be detected to us. Small, cool objects are too faint even for JWST’s powerful detector tools. But JWST isn’t our only chance to find and track the small bodies that live mostly on the fringes of our solar system. Astronomers often discover previously unknown comets in surveys such as the Sloan Digital Sky Survey and Catalina Sky Survey. The European Space Agency’s (ESA) Gaia Observatory and Vera Rubin Observatory will also help discover new comets, possibly increasing our existing list by several orders of magnitude.

And according to Peñarrubia, we can distinguish local comets from interstellar interlopers by their trajectories and motion.

“If we can measure the orbit of a large number of objects — which is going to happen in the next few years, then we should start to see this kind of distinct population, which is probably also distinct in composition,” Benarobia says. “I wouldn’t be surprised if objects that got trapped from the interstellar environment had this different composition than objects that formed in the solar system. So there will be, probably, many different ways of seeing if we can distinguish them from the rest of the comets that form in the solar system.”

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