On September 18, 2009 (July 30, 2009 in the lunar calendar), the first planet with a density close to that of the earth was discovered outside the solar system. Planet COROT-7b conceptual graph According to the website of the US "Wired" magazine, in the vast universe, astronomers have never stopped searching for terrestrial planets outside the solar system. On September 18, 2009, astronomers finally obtained conclusive evidence. They successfully measured the mass of a planet outside the solar system and found that its density is close to that of the earth. This is the first terrestrial planet confirmed by scientists to be close to the density of the earth. Sarah Siegel, a researcher at the Massachusetts Institute of Technology in the United States, said: "This is a day we have been dreaming of for a long time." Although she was not involved in the study, Sara-Siegel still gave a high evaluation of the significance of the study, "This is the first confirmed rocky planet outside the solar system, which opens a new door for us in this field. We are really excited." In fact, as early as February this year, astronomers discovered the planet COROT-7b, but its mass could not be determined at that time. Later, scientists used the "High Accuracy Radial Velocity Planet Finder" (HARPS) spectrometer to observe up to 70 hours of data, and scientists from the European Southern Observatory (EuropeanSouthernObservatory) calculated that the planet is only more than five times the mass of Earth. Based on the known diameter of the planet, which is about twice the diameter of the earth, scientists calculated the density of the planet, and finally concluded that this is the first extrasolar Earth-like planet with a density similar to that of the earth. Is there a planet similar to the earth in the universe? Is our earth the unique pride of the universe? This is a very profound question. So far no one has given a positive or negative answer. In fact, so far scientists have discovered about a dozen smaller planets similar to the earth, and in the process of discovering COROT-7b, astronomers also discovered a sister planet called COROT-7c. In addition, astronomers have discovered several planets in the Milky Way with rocky surfaces similar to Earth's. But they are much more massive than Earth, and they lack sun-like planets that orbit around them. Instead, they orbit dead bodies. But most planets are giant gas planets, like Jupiter and Saturn in our solar system. Gas planets may not have solid surfaces, but are mainly composed of hydrogen, helium and water in different physical states. Astronomers' efforts are not limited to finding Earth-like planets, but also to explore whether there are Earth-like planets that are suitable for alien life. Siegel said humans are most likely to find alien life on a rocky planet that is close to Earth's density and is less dense. "The holy grail of exoplanet research, even scientific research, is to find planets similar to Earth, to find Earth-like planets with signs of life," she said. Although COROT-7b has a density similar to that of Earth and is also a rocky planet, the temperature of the planet can reach 2,000 degrees Celsius during the day and drop to minus 200 degrees Celsius at night. Scientists believe that the environment of COROT-7b is too cruel for life. In addition to being the first rocky earth planet confirmed to be close to Earth's density, COROT-7b is closer to its host star than any other known planet. COROT-7b orbits its host star at a record speed of 750,000 kilometers per hour. Scientists speculate that the planet's environment is very harsh, with surface magma gushing or boiling oceans. Because it is the first Earth-like planet discovered outside the solar system with a density close to that of Earth, scientists do not know what secrets are still hidden on this planet, which needs to be further studied and discovered. Just before scientists announced the mass of COROT-7b last week, Greg, an astronomer at the University of California, expressed his excitement. He said: "We don't know how to define a planet that is five times the mass of Earth. It can be said to be a large Earth, or it can be said to be a super Earth. Or a small Neptune, a small Uranus. This is really a basic type of planet that we have never seen before." Comment: Hope humans can find biological species in outer space soon.