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On October 17 and 18, 2017, an unusual object crossed the field of view of a large telescope placed near the top of a volcano on the Hawaiian island of Maui. The Pan-STARRS1 telescope is designed to survey the sky for temporary phenomena such as approaching asteroids or comets. But this was different. The object was not bound by gravity to the Sun or any other celestial body. It was coming from somewhere else.
This mysterious object was the first visitor from interstellar space observed to pass through our solar system. Astronomers named it 1I/’Oumuamua, borrowing the Hawaiian word for “the first messenger to arrive from afar.” Two years later, in August 2019, amateur astronomer Gennady Borisov spotted the only other known interstellar interloper, now called 2I/Borisov, with a home-built telescope at the MARGO Observatory in Naushny, Crimea. discovered using.
Although typical, asteroids and comets In a solar system orbiting the Sun, ‘Oumuamua and Borisov are celestial nomads who spend most of their time wandering through interstellar space. The existence of such an invader in our solar system had been hypothesized, but scientists expected it to be rare. “We never thought we would be able to observe it,” says astrophysicist Susanne Falzner of Germany’s Jülich Supercomputing Center. At least not in her lifetime.
With these two discoveries, scientists now suspect that interstellar invaders are much more common. Currently, there may be about 10,000 ‘Oumuamua-sized interstellar objects within Neptune’s orbit alone, estimates UCLA planetary scientist David Jewitt, co-author of the brief. Current understanding of interstellar invaders in 2023 Annual Review of Astronomy and Astrophysics.
Researchers are busy answering fundamental questions about these alien objects, such as where they came from and how they ended up wandering the galaxy. Intruders could also provide new ways to explore features of distant planetary systems.
But first astronomers need to discover more of them.
“We’re a little behind the curve at the moment,” Jewitt said. “But we expect more.”
origin of aliens
Astronomers have considered the possibility of interstellar objects since at least the early 18th century. Recently, computer models showed that our solar system long ago sent its own small celestial bodies into the interstellar void through gravitational interactions with giant planets.
Scientists expected most of the invaders to be exocomets made of icy material. Borisov fits this profile. It had a tail made of gas and dust produced by ice that evaporated during its approach to the Sun. This suggests that it originated in the outer regions of the planetary system, where temperatures are cold enough for gases such as carbon monoxide to freeze into rocks. At some point, something threw Borisov out of the system about a kilometer in diameter.
One potential cause is stellar flybys. According to one paper, the gravity of a passing star could knock small objects known as planetesimals out of the system. Recent research led by Falzner. Additionally, if an asteroid or comet gets close enough to the planet’s gravitational pull to speed up the smaller object and escape the star’s control, the giant planet could eject the object from the outer regions of the planetary system. Close encounters can also occur when planets move through planetary systems, as Neptune is thought to have done in the early solar system.
“Oumuamua, on the other hand, is not what scientists expected. Observations suggest that the bridge is quite elongated, perhaps 240 meters long and 40 meters wide. Also, unlike Borisov, it is No dust activity was observed, raising the possibility that it occurred near a star where ice is too hot to form. If this is the case, a flyby of the star or a giant planet is likely the object. could not have been pulled out of its system. Instead, it may have been ejected during its star’s death throes. A pulse of gas from the dying star could have pushed planets and planetesimals outward. could destabilize their orbits enough to send some of them into interstellar space.
However, it is possible that ‘Oumuamua actually formed in the cold outer region of the system and developed a gas tail that is undetectable by telescopes as it approaches the Sun. One clue is that the object sped faster than expected from the solar system’s gravity alone. According to recent research, Such an increase may have been caused by the release of small amounts of hydrogen gas It could not be detected with a telescope. There are several asteroids in our solar system A similar boost could be obtained by outgassing water vapor, according to another study. future observations with the James Webb Space Telescope, JAXA Hayabusa2 extended mission (scheduled to merge with one of these solar system asteroids, known as the “dark comet”, in 2031) could detect low-level outgassing.
“We’ll have to wait and see, but they could be ‘Oumuamua analogs,” said Cornell University planetary scientist Darryl, who co-authored the interstellar interloper review with Jewitt. Seligman says.
looking for nomads
More data from more intruders may help answer some of these questions. To collect these data, scientists need a higher probability of detecting objects as they pass through our solar system. “If Pan-STARRS1 hadn’t observed where we went that night, ‘Oumuamua likely would have never been discovered,” said the former Hawaiian who discovered the intruder from telescope data. says university astronomer Robert Werick.
from now on Space-time heritage investigation It is hoped that observations from the Vera C. Rubin Observatory will increase the chances that astronomers will discover these fast-moving objects. Starting as early as 2025, the observatory’s telescope will photograph the entire visible southern sky every few nights, and its primary mirror is nearly 7 meters in diameter. It can see larger, farther and darker objects than Pan-STARRS1. Once an intruder is detected, ground-based and space-based telescopes photograph the intruder and try to determine what it is made of. And if a reachable target is discovered, the European Space Agency and the Japan Aerospace Exploration Agency will comet interceptoris scheduled to launch in 2029 and may redirect visitors for up-close photos.
Ultimately, astronomers Exoplanet inventorySince its first discovery in 1992, the number of registrations has grown to more than 5,500. That future inventory could help researchers answer the long-standing question of what Earth and the solar system are typical of. The composition of a large sample of interstellar objects may provide clues about the composition of bodies in exoplanetary systems, including systems that may support life.
“Planesimals are the building blocks of exoplanets,” says Meredith Hughes, an astronomer at Wesleyan University in Middletown, Connecticut. This means they “can provide information about the diversity of environments, including habitable environments.”
Now, “Oumuamua is outside the orbit of Neptune, and Comet Borisov is about the same distance away.” They continue their journey again interstellar space, no one knows what will happen next. Perhaps they will wander forever in the vast void of space, or perhaps they will be captured by a star. Or they could disintegrate into a disk of gas and dust that evolves in a new planetary system and begin their journey again.
Astronomers estimate that the Milky Way may contain more interstellar objects than stars in the observable universe. Finding more of them will provide new ways to explore the mysteries of the universe.
“What’s really amazing is that interstellar objects come to us,” Falzner said.
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