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Where Did the Mysterious Interstellar Visitor 'Oumuamua Come From?

Updated: Aug 3

In 2017, astronomers discovered the first known interstellar object to visit our solar system. The object called 'Oumuamua is very strange, and it is hard to explain where it came from. Researchers have now come up with explanations on the features of 'Oumuamua and have likely determined its origin. In this article, we will delve into the details of the research and findings on where 'Oumuamua came from.

The Mystery of 'Oumuamua

Astronomers were left puzzled when they spotted a strange object speeding away from the sun at 50 miles per second on October 19, 2017. They called it 'Oumuamua, a Hawaiian word for "scout" or "messenger." The trajectory of the object indicated that it had come from outside the solar system and that after a brief buzz past the inner worlds of our system, it was bound for deep space. By the time it was noticed, it had already passed Earth.

A 3D illustration of the interstellar object known as 'Oumuamua.

A 3D illustration of the interstellar object known as 'Oumuamua. (Image Credit: Getty Images)

Scientists observed that the object resembled a comet, but unlike any comet that had ever been observed in the solar system. It lacked any kind of cometary tail, and its pancake shape was more flattened than any other known solar system object in terms of size. Researchers determined several characteristics of the object, including its speed, size, composition, etc.

Determining the Origin of 'Oumuamua

Astrophysicists from Arizona State University recently came up with an explanation for the features of 'Oumuamua. They likely have determined its origin. They found that this interstellar object is likely a piece of a Pluto-like planet from another solar system.

Steven Desch of the School of Earth and Space Exploration said, "In many ways, 'Oumuamua resembled a comet, but it was peculiar enough in several ways that mystery surrounded its nature, and speculation ran rampant about what it was."

Desch and his colleague Alan Jackson calculated how the ices in 'Oumuamua would sublimate as the object acquired a push by the sun. They found that solid nitrogen ice provided an exact match to all the object's features simultaneously. Since solid nitrogen ice can be seen on the surface of Pluto, it is possible that a comet-like object could be made of the same material.

'Oumuamua's Journey to Our Solar System

In the scenario favored by Desch and Jackson, the nascent 'Oumuamua was knocked from a Pluto-like object that was circling a distant star some half-billion years ago. It would have originally been roundish, but as it traveled through space, it was carved away by cosmic rays.

This very deep combined image shows the interstellar object ‘Oumuamua at the center of the image. It is surrounded by the trails of faint stars that are smeared as the telescopes tracked the moving comet.

This very deep combined image shows the interstellar object ‘Oumuamua at the center of the image. It is surrounded by the trails of faint stars that are smeared as the telescopes tracked the moving comet. (Image Credit: ESO/K. Meech et al.)

By the time it entered our solar system in 1995 or so, it had lost half its original mass, according to their model. During its passage around the sun, it likely melted to a sliver, like a bar of soap in the shower, the researchers say. Only 10 percent would have remained by the time it left the solar system, boosted by the rocket-like effect of evaporating nitrogen.

Desch said, "Everybody is interested in aliens, and it was inevitable that this first object outside the solar system would make people think of aliens. But it's important in science not to jump to conclusions. It took two or three years to figure out a natural explanation -- a chunk of nitrogen ice -- that matches everything we know about 'Oumuamua. That's not that long in science, and far too soon to say we had exhausted all natural explanations."

Moving Groups of Interstellar Objects

Each star is moving around the galaxy at its own pace, and together they form moving groups that are related to their point of origin, which, in turn, corresponds with their intrinsic chemistry. The populations of stars belonging to each disk have different velocity distributions. Because the interstellar objects (ISOs) that they eject share a similar velocity as their parent star relative to the sun, they tend to stick to the same moving groups, but these moving groups criss-cross the sun's path all the time.

"The sun is essentially running into them," said Matthew Hopkins of the University of Oxford. This means that we should preferentially expect to see ISOs coming from the "solar apex," which is the direction of the sun's motion relative to other nearby stars.

Coming from this direction means that they'll make their closest approach to the sun, where they are easiest to detect, while they are in the Southern Hemisphere sky -- the same sky that the new Vera Rubin Observatory will be surveying. It is expected that Vera Rubin will discover hundreds of new ISOs.

Slower ISOs Contain Less Water

The lower an ISO's relative velocity compared to the sun, the more likely it is that it will fall into the inner solar system where we can detect it. An ISO's relative velocity is related to the relative velocity of its parent star, which depends significantly on whether that star hails from the thin disk with more heavy elements or from the thick disk with fewer heavy elements. The lower-velocity ISOs (relative to the sun) are expected to come from the thin disk, where stars and their accompanying planetary systems form from gas and dust that contain more heavy elements. The more heavy elements there are in the disk of gas and dust that forms planets and comets, the smaller the fraction of water an ISO will have.

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This is because a protoplanetary disk rich in heavier elements contains a lot of carbon, and carbon (as well as iron, magnesium, silicon, and sulfur) is adept at plucking up all the free oxygen atoms, two at a time, to form molecules of carbon dioxide. Water can only form from any oxygen atoms that are left over, meaning that ISOs forming within these disks generally possess a lower fraction of water.

The mystery of 'Oumuamua's origin has been solved, and it is likely a piece of a Pluto-like planet from another solar system. ISOs like 'Oumuamua are the most numerous objects in the Milky Way galaxy. The discovery of hundreds of new ISOs by the Vera Rubin Observatory will provide a fuller picture of where they are coming from and what their chemical properties are. The research on ISOs is important in understanding the composition and formation of planetary systems in our universe.

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