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Zakrycia asteroid pozasłonecznych

An interstellar object is a body, other than a star or substar, that is located in interstellar space and is not gravitationally boundto a star. The term can also be applied to objects that are on an interstellar trajectory but are temporarily passing close to a star, such as certain asteroids and comets (including exocomets[1][2]).

Due to present observational difficulties, an interstellar object can usually only be detected if it passes through the Solar System, where it can be distinguished by its strongly hyperbolic trajectory, indicating that it is not gravitationally bound to the Sun.[2][3] In contrast, gravitationally bound objects follow elliptic orbits around the Sun, like most asteroids, comets, and objects in the Oort cloud.

It is possible for objects orbiting a star to be ejected due to interaction with a third massive body, thereby becoming interstellar objects. Such a process was initiated in early 1980s when C/1980 E1, initially gravitationally bound to the Sun, passed near Jupiter and was accelerated sufficiently to reach escape velocity from the Solar System. This changed its orbit from elliptical to hyperbolic and made it the most eccentric known object at the time, with an eccentricity of 1.057.[4] It is headed for interstellar space.

The first discovered, and to date only known, interstellar object is ʻOumuamua (1I/ʻOumuamua, previously called C/2017 U1 and A/2017 U1). The object has an orbital eccentricity of about 1.20, making it impossible for it to originate from our Solar System.

Recent research suggests that asteroid (514107) 2015 BZ509 may be a former interstellar object, captured some 4.5 billion years ago, as evidenced by its co-orbital motion with Jupiter and its retrograde orbit around the Sun.


With the first discovery of an interstellar object, the IAU has proposed a new series of small-body designations for interstellar objects, the I numbers, similar to the comet numbering system. The Minor Planet Center will assign the numbers. Provisional designations for interstellar objects will be handled using the C/ or A/ prefix, (comet or asteroid) as appropriate.[6]

1I/2017 U1 (ʻOumuamua

A dim object was discovered on October 19, 2017 by the Pan-STARRS telescope, at an apparent magnitude of 20. The observations showed that it follows a strongly hyperbolic trajectory around the Sun at a speed greater than the solar escape velocity, in turn meaning that it is not gravitationally bound to the Solar System and likely to be an interstellar object.[14] It was initially named C/2017 U1 because it was assumed to be a comet, and was renamed to A/2017 U1 after no cometary activity was found on October 25.[15][15][16] After its interstellar nature was confirmed, it was renamed to 1I/ʻOumuamua – ‘1’ because it is the first such object to be discovered, ‘I’ for interstellar, and “‘Oumuamua” is a Hawaiian word meaning “a messenger from afar arriving first”.[17]

The lack of cometary activity from ʻOumuamua suggests an origin from the inner regions of whatever stellar system it came from, losing all surface volatiles within the frost line, much like the rocky asteroids, extinct comets and damocloids we know from our Solar System. This is only a suggestion, as ʻOumuamua might very well have lost all surface volatiles to eons of cosmic radiation exposure in interstellar space, developing a thick crust layer after it was expelled from its parent system.

ʻOumuamua has an eccentricity of 1.199, which is the highest eccentricity ever observed for any object in the Solar System by a wide margin.

In September 2018, astronomers described several possible home star systems from which ‘Oumuamua, that was detected passing through the Solar System in October 2017, may have begun its interstellar journey.[18][19]

In November 2018, Harvard astronomers Amir Siraj and Avi Loeb reported that there should be hundreds of ‘Oumuamua-size interstellar objects in the Solar System, based on calculated orbital characteristics, and presented several known examples, namely, 2011 SP252017 RR22017 SV13, and 2018 TL6.[20] These are all orbiting the sun, but with unusual orbits, and are assumed to have been trapped at some occasion.