2020-11-03

27,000 light-years away, an earth-sized planet wanders lonely, but it shows its feet here

By yqqlm yqqlm

In the universe, not all planets are as lucky as the earth, able to revolve around their host star, gaining light and heat. Scientists’ research shows that there are many wandering planets in the universe. They have no companions, and they shuttle through interstellar space alone.

The Lonely Wanderer

Some scientists believe that there are billions of wandering planets in the galaxy alone. But it is too difficult for us to discover these planets. In the night sky, planets such as Venus, Jupiter and Mars are the brightest celestial bodies because they reflect a lot of sunlight. The wandering planets are different. They are much farther from us than the eight planets, and they are not illuminated by their host stars, so it is almost impossible to observe them directly.

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Therefore, four Among the thousands of exoplanets, only a few are wandering planets, and some of them are only suspected, not and difficult Be confirmed.

Even so, scientists have put forward some inferences based on existing knowledge. They believe that:Most of the wandering planets we can observe are very huge, with masses between 2-40 times Jupiter. . However, just recently, scientists have really discovered a small wandering planet whose mass is about the same as that of the earth. With its thin body, it wanders in the center of the Milky Way.

According to a paper published in the Astrophysical Journal Newsletter on October 29, this is likely to be the smallest wandering planet ever discovered by mankind. If this is the case, it will prove some theories that have been pending for a long time.

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The main author of the paper is Przemek, a postdoctoral fellow from California Institute of Technology Mroz said:”The probability of detecting such low-mass objects is very low, so either we are lucky enough, or these objects are very common in the Milky Way, and may even be seen everywhere like stars.”

Einstein’s convex lens

Then, several times more than Jupiter Giant wandering planets of mass are difficult to observe. Why can they find such a small one this time?

In fact, scientists did not observe it directly, but discovered it indirectly. The method they used is exactly what Einstein’s general theory of relativity gave us:gravitational lensing method.

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We knew when we were in middle school that light travels in a straight line . But under the action of celestial-scale gravity, space will be distorted. Although light does not turn in the space it passes through, its path is distorted along with the space. Therefore, if a celestial body moves between a very bright large celestial body and the earth, the light around the background celestial body will slightly converge towards the earth under the gravitational distortion of the foreground celestial body, forming a convex lens effect, and can make the background like a convex lens. The visual brightness of celestial bodies increases, so this method is called gravitational lensing.

Generally speaking, we will use the galaxy-scale strong gravity to observe the background galaxy. In this case, the light distortion is more obvious. However, if the instrument is sophisticated enough, it can also be used to observe the gravitational lensing effect produced by planets. Scientists have previously made some discoveries on exoplanets with host stars. For the wandering planet, although it does not have the light of the host star to be distorted, it can also produce gravitational lensing when passing through other bright celestial bodies. This is the important reason why it was discovered this time.

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Difficulty Still exist

Even so, the size of the wandering planet still largely determines the difficulty of observation by scientists. The smaller the foreground celestial body, the smaller the degree of light distortion caused by the background celestial body, and the shorter the observation time left for us. According to the researchers, if the wandering planet has several times the mass of Jupiter, then the gravitational lensing effect it produces will be observed by us within a few days; but for planets of earth mass, it can only make the background celestial bodies The brightness increases in a few hours or even less, and then it recovers completely. Therefore, scientists specifically call these micro-gravitational lensing phenomena.

Mroz pointed out:”The probability of observing micro-gravitational lensing is very small. If we only stare at a source celestial body, we may have to wait at least 1 million years to see it appearing micro-gravitational lensing.”

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The smallest wandering planet

Therefore, instead of doing this almost futile behavior, they expanded the search range and observed hundreds of millions of stars at the same time, which can greatly increase the probability of observation. Fortunately, the University of Warsaw in Poland and other institutions are conducting such a project, which is Optical gravitational lens experiment. Since 1992, they have discovered at least 17 exoplanets.

Using this project, Mroz and his team observed the center of the Milky Way galaxy, looking for clues to the phenomenon of micro-gravitational lensing.

Finally, in June 2016, they captured the shortest microgravitational lensing event so far, which only lasted 42 minutes. They immediately realized that something unusual had happened at the center of the Milky Way, 27,000 light years away!

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It is estimated that the mass of this celestial body is about Between 0.5-1 Earth mass, which means it is a planet, and most likely a rocky planet. Its quality is difficult to determine because the distance between it and the source object cannot be measured yet. But no matter the upper limit or the lower limit of the theoretical mass, it is enough to make it deserve to be the smallest wandering planet ever discovered by mankind. Mroz proudly said:This will be an”important milestone” in the theory of human planet formation.

Studies have shown that within the range of at least 8 astronomical units (1.2 billion kilometers) around the foreground celestial body, no stars have a gravitational effect on it. It is speculated that it may have revolved around a star, but because it accidentally moved to the side of a giant planet, it was thrown out of its own system and became a lonely walker.

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Asteroid, the big secret

The appearance of this planet also verified some previous theories. Mroz said:“Planet formation theory has predicted that most wandering planets should be the same mass as the earth or smaller, but this is the first time we have actually discovered such celestial bodies. Einstein’s theory allows us to detect It’s really incredible to see such a small “stone” wandering in the Milky Way.”

One of the participants in this study, Radek Poleski of the University of Warsaw, said confidently:like Such rocky planets are likely to be discovered in large numbers. Relying on the nearly 30-year-old optical gravitational lens experiment, and the future NASANancy Roman Space Telescope, human observing ability will be further improved, discover more smaller and darker celestial bodies, and unlock more secrets of the universe.

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These planets, they are wandering, but they are no longer alone.