ESO / M KORNMESSER
On October 19, 2017, astronomers who examined images of the Pan-STARRS telescope in Hawaii noticed a point source of light moving rapidly on a path away from the Sun.
At that time they did not realize we were looking at one of the most significant events in the history of astronomy.
Initially, astronomers thought it was a comet, but after it did not degas the volatiles trapped in the icy body of a comet when it approaches the Sun, it concluded that it must be an asteroid.
Asteroids are rocks that generally orbit around the Sun in a region called the Asteroid Belt located between the orbits of Mars and Jupiter. A gravitational instability of the planets in orbit and the Sun can occasionally pull an asteroid and send it into an orbit closer to the Sun.
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Astronomers gave this newly detected piece of rock an asteroid name, A / 2017 U1 (A is for asteroid and U designates the period in the year in which it was discovered, from October 16 to October 31).
Robert Weryk of the University of Hawaii, began performing routine observations of reflected light from this object to learn more about its trajectory. It was too small and too distant for anything more than a point source of light to be observed, even using the most powerful telescopes.
However, the analysis of this light revealed that it was an unusual pencil-shaped rock. Its variable brightness observed was consistent with the fall. The falling asteroids are not unusual, but Weryk was amazed by their speed and trajectory: they were unique.
Each previously observed moving object in our Solar System moves in an elliptical orbit around the Sun, which includes comets, asteroids, and planets. The degree of stretch of the ellipse is called its eccentricity.
An ellipse has an eccentricity of less than 1; a circle has an eccentricity of 0. The orbit of the Earth is almost circular, with an eccentricity of only 0.017. One of the most elliptical elliptical orbits that has been observed is Halley's Comet, its eccentricity being 0.967.
If the trajectory of an object in the Solar System is circular or elliptical, it must be gravitationally captured, that is, in orbit around the Sun. But this mysterious elongated bundle of rock moved in a trajectory with a measured eccentricity of 1.2, the highest ever recorded. Having an eccentricity greater than 1 means that it is not elliptical, but hyperbolic.
Hyperbolic trajectories never orbit around a central mass; this object can not be gravitationally bound to the Sun, but simply diverted by the Sun as it passes through the Solar System.
The speed of this object was also high, 88 kilometers per second at its closest point to the Sun. For an object to orbit around the Sun, it must move at a speed lower than that of the Sun (80kms per second under these conditions).
Astronomers concluded that this strange pencil-shaped rock must be a traveler from deep interstellar space. the first known interstellar object that ever passed through the Solar System. This was a significant astronomical event; the observations and the analysis were immediately published in the prestigious scientific journal Nature on November 20, 2017.
The International Astronomical Union had to invent a new designation system for this first known interstellar object, 1I / 2017 U1, in which "I" means interstellar.
It was given the name, "Oumuamua", the Hawaiian "explorer". The first symbol is not an apostrophe but a glottal stop, a type of Hawaiian consonantal sound.
& # 39; It is estimated that Oumuamua is about 230 meters long and 35 meters wide, has a reddish hue due to its exposure to many millions of years to cosmic radiation and is probably a dense rock rich in metals.
Cosmic rays are high energy, coming mainly from stellar events outside the Solar System, although our Sun also produces cosmic rays.
& # 39; Oumuamua came from the general direction of the Lyra constellation and has probably been traveling for billions of years.
It is now moving away from the Sun and it will take 20,000 years to completely abandon the Solar System, after which it will travel once again through interstellar space for many tens of millions of years before its next encounter with some other distant solar system.