Alien spacecraft? Asteroid? Five years ago, its arrival puzzled scientists

No romance can compare to the sea of ​​stars

People are always far away from the unknown

Have beautiful yearning and expectations

If you are because of aliens or alien civilizations

I became interested in astronomy

So, a little guy named "Oumuamua"

Maybe to some extent

Satisfy your imagination of astronomical exploration

Image source: NASA

Five years ago today (October 19), humans discovered the extrasolar object "Oumuamua" in the solar system for the first time.

As the first interstellar object to be visited from outside our solar system, both scientists and netizens have shown great interest in it.

An alien spaceship? A comet from another galaxy? An asteroid? ... The question of what it is has stumped countless astronomers around the world.

Comments from netizens

In the vast universe, how was "Oumuamua" discovered?

Although Oumuamua is the first interstellar object to visit our solar system, there is nothing special about its discovery process. It is the result of an ordinary observation in the Pan-STARRS project (a sky survey exploration project that aims to discover potential new near-Earth objects, such as comets, asteroids, variable stars, etc., by comparing images of the same area of ​​the sky at different times).

On October 19, 2017 Beijing time, astronomer Robert Weryk discovered Oumuamua about 30 million kilometers away from the Earth. At this time, it was flying away from the solar system at a speed of about 26km/s.

Scientists then checked the data and found the image of Oumuamua taken on October 18.

In the following days, the European Space Agency (ESA) Optical Ground Station (OGS) telescope also found some previous data. On October 26, 2017, scientists confirmed the image of Oumuamua twice from the data of the Catalina Sky Survey on October 14 and October 17.

Is “ABB” naming also popular among interstellar bodies?

The first problem to be solved for a new celestial body is how to call it.

The International Astronomical Union (IAU) is the main body recognized by astronomers around the world for naming celestial bodies.

In order to give any celestial body a clear name, the society established a naming system that can systematically name and arrange the order of various celestial bodies.

When a celestial body is discovered, it is first given a category number after verification by astronomers and various observations. For comets, asteroids or satellites of planets, a separate meeting is held to pass another English name as its inherent name to replace the difficult-to-remember number.

Image source: NASA

On November 6, 2017, based on the time of discovery and category, the first interstellar object visiting from outside our solar system was given a permanent scientific name 1I/2017 U1 by the International Astronomical Union. The letter I in "1I" stands for interstellar object, and 1 is the first of its kind.

However, in the process of communication, nicknames are often easier to remember, so in addition to the scientific name, as the discoverer of the celestial body, the scientists of the Pan-STARRS telescope chose to name it using the local Hawaiian (where the Pan-STARRS telescope is located) dialect "ʻOumuamua", which means "messenger from afar". The Chinese name "Oumuamua" is also transliterated from this.

Oumuamua has many other names, such as C/2017 U1 (PANSTARRS), A/2017 U1, etc.

Why can it be remembered by mankind?

Based on observations, scientists found that Oumuamua looks like a long and thin cigar.

Due to the influence of cosmic ray radiation, the surface appears reddish and has a solid surface, but it cannot be distinguished whether it is made of rock or metal.

It is estimated to be 400 meters long and 40 meters wide, which is larger than most asteroids or comets observed in the solar system. At the same time, it rotates rapidly during its movement, and its rotation axis is not fixed.

In addition to its strange appearance, its incredible acceleration ability and trajectory have also attracted the attention of scientists.

Oumuamua entered the solar system almost perpendicular to the ecliptic plane.

According to calculations, before entering the solar system, Oumuamua's speed was only 26km/s, but it was also far greater than the solar system escape velocity of 16.7km/s (the third cosmic speed).

When Oumuamua reached perihelion, its speed increased to 87km/s, and then it traveled from the orbit of Neptune into deep space at a speed of 40km/s.

Image source: Internet

Based on observations, scientists have calculated that the eccentricity of Oumuamua's orbit is as high as 1.2.

When the eccentricity is 0, the object's orbit is circular; when the eccentricity is less than 1, the object's orbit is elliptical, which is the common planetary orbit; when the eccentricity is greater than 1, the orbit is a parabola.

Oumuamua entered the solar system with such a high eccentricity that the Sun will not be able to capture it and it will eventually fly out of the solar system.

Image source: NASA

In addition, there is also the mystery of its origin, which is also controversial.

For example, the comet dispute. Before Oumuamua, existing planetary system theories believed that comets were more likely to be "thrown out" by their original planetary systems.

Based on past human observation experience, since comets are brighter than asteroids of the same size, most observable interstellar objects are also comets.

However, according to telescope observations, Oumuamua did not have the obvious feature of a comet, such as a comet tail, so some scientists denied that Oumuamua was a comet.

Other scientists believe that Oumuamua is still a comet. Only icy celestial bodies such as comets will evaporate when they are close to the sun. The jet gas produced by evaporation generates thrust, which causes Oumuamua's speed to increase.

For example, is it an asteroid? Based on this speculation, some astronomers began to take action again.

But what frustrates them is that Oumuamua is an "invisible guest" - with existing technology, humans find it difficult to capture its movement speed and brightness, and can only obtain a rough spectrum that does not contain detailed information on the object's reflectivity.

Image source: Internet

For example, Oumuamua is an artificial light sail spacecraft that passed through the solar system for exploration. Its non-gravitational acceleration phenomenon was achieved by using the pressure of sunlight.

Scientists at Yale University also believe that Oumuamua most likely came from a molecular cloud millions of light years away from Earth, and it is a group of gas or dust in the molecular cloud.

A study completed by Dr. Zhang Yun of the National Astronomical Observatory of the Chinese Academy of Sciences and Professor Lin Chao of the University of California, Santa Cruz, believes that this "interstellar visitor" may be a fragment of a planetary body - possibly fragments torn apart and thrown out by the tidal effects of the star in the protoplanetary system.

The tidal disruption process of a close flyby of a star (Source: National Astronomical Observatory)

In the five years since the discovery, scientists have produced many research results through observation and research.

But it has flown too far to be detected by any human telescope.

Just like that, before people could see it clearly, this mysterious interstellar visitor who came and went in a hurry "disappeared", leaving behind many unsolved mysteries.

According to scientists' speculation, it will be about 2,300 years before Oumuamua completely leaves the solar system and heads towards the center of the Milky Way to continue its lonely and long journey!

Sources:

Popular Science China, China Youth Daily, National Committee for the Examination of Scientific and Technological Terms, China Economic Net, The Paper, China News Service, Science and Technology Life Express, Astronomy Online, Zhihu

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Author of this article/Xiao Chunfang

Editor/Muzi