In our solar system, astronomers have currently discovered 8 planets.
Among them, the Earth is the only planet with life and civilization, and the Milky Way in which the solar system is located has 100 billion to 400 billion stars, and it can be said that each star system may be a world with life.
The astronomical community refers to planets outside the solar system as exoplanets, such as Proxima B, which is 4.22 light-years away, which is a typical exoplanet, and the so-called "super-Earth" and "second Earth" that have attracted much attention are also exoplanets, such as Kepler 452b and Kepler 22b 638 light-years away.
But you may have noticed that although these exoplanets are outside the solar system, they are still inside the Milky Way, because the diameter of the Milky Way reaches 180,000 light-years, and these exoplanets are only a few hundred light-years or thousands of light-years away from Earth, so are there any extra-Milky Way exoplanets? Or are exoplanets located in other galaxies, such as the Andromeda Galaxy or the Greater Magellanic Galaxy?
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According to the latest issue of Nature Astronomy, astronomers from Harvard University have discovered an exoplanet outside the Milky Way for the first time, but it is not in the large Magellanic Galaxy closest to Earth, nor in the 2.5 million light-year Andromeda Galaxy, but in the M51 galaxy 28 million light-years away.
In fact, astronomers found that this planet, there is a lot of luck in it, because M51 is strictly two galaxies, but the two galaxies are currently colliding, of which M51a is 76,000 light-years in diameter, M51b belongs to the dwarf galaxy, the diameter is slightly smaller.
Astronomers first noticed the colliding galaxy because M51a had a bright radio source inside, it could be a black hole, it could be a pulsar, and coincidentally, when the astronomical community observed this radio source, it found that its brightness would drop rapidly and then recover every once in a while, so astronomers believed that there must be a planet in the orbit of this radio source.
When the planet's orbital power source is between the radio power and the Earth, a part of the radio power will be blocked by the planet, resulting in the fact that the brightness of the astronomers will decrease, and when the planet's orbital position is staggered with the Earth, the brightness of the radio source will be restored, so that after a cycle of cycles, the exoplanet 28 million light-years away is discovered.
This method of determining the existence of planets by observing periodic changes in the brightness of the target celestial body, known in astronomy as transit, is an astronomical phenomenon widely present in the universe.
For example, on Earth, we can often see the news of the transit of the space station, that is, the space station just flew from the surface of the sun, in addition to the transit of Mercury.
With the data collected so far, the extragalactic planet, which is 28 million light-years away, is about 760 times the size of Earth, almost the same size as Saturn, but it is not known whether it will have the same rings as Saturn.
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The discovery of this exoplanet can be said to once again prove the fact that there are a large number of planets in the universe, and according to the Drake formula proposed by the American astronomer Drake, after taking into account the ratio of planets to stars and the ratio of life to higher intelligent life.
There are at least 12,000 intelligent civilizations in the Milky Way alone, and there are hundreds of billions or even trillions of galaxies in the universe like the Milky Way, which is why most scientists believe in the existence of extraterrestrial life or alien civilizations, after all, the base is really too large.
Unsurprisingly, extraterrestrial life doesn't actually need to run outside the solar system, and mars that are close at hand and Jupiter and Saturn that are a little farther away have hope, because in the early solar system billions of years ago, Mars was still the same planet with oceans and atmospheres as Earth today, as did the moons of Jupiter and Saturn.
So correspondingly, the birth and evolution of life that occurred 3.8 billion years ago in the depths of the Earth's oceans is also likely to occur on Mars and Jupiter and Saturn, because the birth of life is essentially a matter of probability, as long as all the conditions are available, the birth of life may only be a matter of time.
Hopefully, one day in the future, humanity will be able to find life from other planets, because it means that human civilization will no longer be alone in the universe.