Interstellar object
Interstellar objects are celestial bodies that originate outside our solar system and travel through it. The first confirmed interstellar object, 'Oumuamua, was detected in October 2017 by astronomer Rob Weryk using the Pan-STARRS1 telescope in Hawaii. Unlike typical comets, 'Oumuamua presented unique characteristics, such as a highly elongated, oblong shape and a lack of a cometary tail, which challenged existing astronomical theories. Its trajectory indicated it had traveled for an extensive period before encountering the solar system, likely coming from the direction of the star Vega.
In 2019, a second interstellar object named 2I/Borisov was discovered, displaying classic cometary features, thereby supporting the idea that many interstellar visitors may resemble comets. While the detection of interstellar objects was once deemed unlikely, advancements in telescope technology are expected to increase their discovery rate significantly. Astronomers anticipate that specialized observatories, like the Vera C. Rubin Observatory, could uncover around one hundred interstellar objects annually, providing deeper insights into these enigmatic visitors from beyond our solar system.
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Interstellar object
Interstellar objects are celestial objects that travel through the solar system, but originate from outside the solar system. Astronomers have long suspected that such objects periodically pass through the solar system, but until recently, they did not have the necessary equipment to see the interstellar visitors. In October 2017, astronomer Rob Weryk used the University of Hawaii’s Pan-STARRS1 telescope to successfully detect the first known interstellar object. His findings were later verified by astronomers across the globe. The object, named ‘Oumuamua, was following a trajectory that began somewhere outside the solar system.
‘Oumuamua surprised astronomers because it did not display many of the signature features of a comet. Instead, it had features of a comet and others more common in an asteroid. Additionally, the interstellar object was shaped in a manner that astronomers had never encountered in our solar system. It was thin and extremely oblong. This caused astronomers to doubt many of their previous theories, which were based on the belief most interstellar objects would resemble comets. A second interstellar object, quickly named 2I/Borisov, was discovered in 2019. This object was clearly a comet, reaffirming astronomers’ theories and suggesting that ‘Oumuamua may have been an outlier. As technology advances and more powerful telescopes are constructed, astronomers expect to find many more interstellar objects.
Background
Interstellar objects are objects that originate outside the solar system. The solar system is made up of the sun, eight planets, at least five dwarf planets, hundreds of moons, and thousands of asteroids and comets. However, most of the bodies located within the solar system have been around since its formation 4.6 billion years ago. These objects orbit the sun, the large star at the center of the solar system. Astronomers have long been able to calculate the orbits of the planets, moons, and many of the larger celestial objects in the solar system. However, they were only able to theorize that objects from outside the solar system might occasionally pass through the solar system. The odds of an interstellar object actually being visible from Earth were extremely small.
In October 2017, Rob Weryk was working as a postdoctoral researcher at the University of Hawaii Institute for Astronomy. While interpreting data from the University’s Pan-STARRS1 telescope, Weryk noticed a strange object passing through the solar system. Weryk initially suspected that the object was a comet moving at on a strange trajectory at about 196,000 miles per hour (315,430 kilometers per hour). However, upon further investigation of the data, Weryk discovered that the object was not displaying any of the typical behavior of a comet. The object was briefly reclassified as an asteroid before astronomers noted that the object was accelerating. Such behavior was not typical for asteroids, and the researchers once again considered that it may be a comet.
Soon after the object’s discovery, Weryk announced that the object may not be orbiting the sun. Other astronomers across the world turned their telescopes towards the object and began tracking it. After brief calculations, scientists announced that because of the object’s strange trajectory, it could not have originated within the solar system. Instead, the object had traveled through space for an undeterminable amount of time before being pulled towards the sun. After passing through the solar system, the object was on a course that would take it back outside the solar system, likely never to return. Astronomers named the object ‘Oumuamua, a Hawaiian term meaning “a messenger from afar arriving first.”
Overview
Although astronomers suspected the existence of interstellar objects before ‘Oumuamua, most expected that the first interstellar object discovered would be a comet. Comets are most commonly found near the edges of the solar system, where the gravitational pull of the sun is weakest. For this reason, sudden or dramatic celestial events might cause a comet to slip loose of the sun’s gravitational pull, causing the comet to become an interstellar object. Given enough time, these comets might travel through space, eventually encountering another solar system.
‘Oumuamua was unlike any celestial object that astronomers had previously observed. The object was oblong and cylindrical, significantly more elongated than most of the objects in our solar system. Its surface was red, dense, and made of rock or metals. Comets are made of ice, frozen gases, rock, and dust. ‘Oumuamua varied significantly in brightness as it rotated, appearing brighter as more of its surface reflected the light of the sun. It did not display the typical cometary tail that appears when comets approach the sun. However, other astronomers argued that ‘Oumuamua’s lack of a tail might be attributed to its small size.
After studying ‘Oumuamua’s trajectory, astronomers concluded the object came from the direction of the star Vega in the constellation of Lyra. However, it is likely that ‘Oumuamua has been traveling for hundreds of thousands of years. At the time when the interstellar object would have passed near Vega, the star would have been in a different location.
In 2019, a second interstellar object was discovered in the solar system. The object was named 2I/Borisov after Gennadiy Borisov, the Russian astronomer who discovered it. Unlike ‘Oumuamua, 2I/Borisov displayed all the traditional qualities of a comet. It was a large, icy body that developed a cometary tail when it passed near the sun. This validated the theory that most interstellar objects should be comets but also raised further questions about ‘Oumuamua’s oddities.
Because astronomers now have access to equipment capable of reliably detecting interstellar objects, they expect the observations of such objects to quickly increase. More specialized equipment for detecting interstellar objects is currently in development. Astronomers expect that, when completed, the Vera C. Rubin Observatory, formerly called the Large Synoptic Survey Telescope (LSST), would be able to discover about one hundred interstellar objects each year.
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