ʻOumuamua the first known Interstellar object.

ʻOumuamua is the first known interstellar object detected passing through the Solar System. Formally designated 1I/2017 U1, it was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakalā Observatory, Hawaii, on 19 October 2017, approximately 40 days after it passed its closest point to the Sun on 9 September. When it was first observed, it was about 33 million km (21 million mi; 0.22 AU) from Earth (about 85 times as far away as the Moon), and already heading away from the Sun.

ʻOumuamua is a small object estimated to be between 100 and 1,000 metres (300 and 3,000 ft) long, with its width and thickness both estimated to range between 35 and 167 metres (115 and 548 ft). It has a red color, similar to objects in the outer Solar System. Despite its close approach to the Sun, ʻOumuamua showed no signs of having a coma. It has exhibited non‑gravitational acceleration, potentially due to outgassing or a push from solar radiation pressure.Nonetheless, the object could be a remnant of a disintegrated rogue comet (or exocomet), according to astronomer Zdenek Sekanina.The object has a rotation rate similar to the average spin rate seen in Solar System asteroids, but many valid models permit it to be more elongated than all but a few other natural bodies. While an unconsolidated object (rubble pile) would require it to be of a density similar to rocky asteroids, a small amount of internal strength similar to icy comets would allow a relatively low density. ʻOumuamua's light curve, assuming little systematic error, presents its motion as "tumbling", rather than "spinning", and moving sufficiently fast relative to the Sun that it is likely of an extrasolar origin. Extrapolated and without further deceleration, ʻOumuamua's path cannot be captured into a solar orbit, so it would eventually leave the Solar System and continue into interstellar space. ʻOumuamua's planetary system of origin and the age of its excursion are unknown.

Discovery

The first known interstellar object to visit our solar system, 1I/2017 U1 ‘Oumuamua, was discovered Oct. 19, 2017 by the University of Hawaii’s Pan-STARRS1 telescope, funded by NASA’s Near-Earth Object Observations (NEOO) Program, which finds and tracks asteroids and comets in Earth’s neighborhood. While originally classified as a comet, observations revealed no signs of cometary activity after it slingshotted past the Sun on Sept. 9, 2017 at a blistering speed of 196,000 miles per hour (87.3 kilometers per second). It was briefly classified as an asteroid until new measurements found it was accelerating slightly, a sign it behaves more like a comet.

How Oumuamua Got its Name

The object was officially named 1I/2017 U1 by the International Astronomical Union (IAU), which is responsible for granting official names to bodies in the solar system and beyond. In addition to the technical name, the Pan-STARRS team dubbed it ‘Oumuamua (pronounced oh MOO-uh MOO-uh), which is Hawaiian for “a messenger from afar arriving first.

Classification

Initially, ʻOumuamua was announced as comet C/2017 U1 (PANSTARRS) based on a strongly hyperbolic trajectory. In an attempt to confirm any cometary activity, very deep stacked images were taken at the Very Large Telescope later the same day, but the object showed no presence of a coma. Accordingly, the object was renamed A/2017 U1, becoming the first comet ever to be re-designated as an asteroid. Once it was identified as an interstellar object, it was designated 1I/2017 U1, the first member of a new class of objects. The lack of a coma limits the amount of surface ice to a few square meters, and any volatiles (if they exist) must lie below a crust at least 0.5 m (1.6 ft) thick. It also indicates that the object must have formed within the frost line of its parent stellar system or have been in the inner region of that stellar system long enough for all near-surface ice to sublimate, as may be the case with damocloids. [citation needed] It is difficult to say which scenario is more likely due to the chaotic nature of small body dynamics, [citation needed] although if it formed in a similar manner to Solar System objects, its spectrum indicates that the latter scenario is true. Any meteoric activity from ʻOumuamua would have been expected to occur on 18 October 2017 coming from the constellation Sextans, but no activity was detected by the Canadian Meteor Orbit Radar.

On 27 June 2018, astronomers reported that ʻOumuamua was thought to be a mildly active comet, and not an asteroid, as previously thought. This was determined by measuring a non-gravitational boost to ʻOumuamua's acceleration, consistent with comet outgassing. However, studies submitted in October 2018 suggest that the object is neither an asteroid nor a comet, although the object could be a remnant of a disintegrated interstellar comet (or exocomet), as suggested by astronomer Zdenek Sekanina.

 

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