Looking for the “Wandering Earth”

A Song of Qingyun in the pre-Qin era wrote: “Obviously, there are stars in the sky.” The universe is vast, the space is endless, the stars are bright, and the Ganges is sandy. Apart from the earth, is there a planet suitable for human habitation? Humans have been asking this question curiously.

How to discover and observe other planets? A scientist in the United States has devised a way. The principle is this: When the planet moves in front of the star, the brightness of the star will change slightly. For example, when Mercury moves in front of the sun, Mercury will block part of the sun’s light, making the sun’s brightness slightly darker. This phenomenon is called transit, and the method of discovering planets is called “transit method”. The transit method requires higher observation equipment and observation conditions, because the volume of the planet is much smaller than that of the star, and the luminosity change produced by the star during transit is minimal, just like observing a mosquito from a long distance when it flies in front of a bright light bulb. The brightness changes, so the photometric accuracy of the photometer is better than one ten thousandth. Based on this idea and requirement, NASA designed and manufactured the Kepler telescope and sent it to space in March 2009. Compared with the well-known Hubble Telescope, Kepler has a wider field of view. It can observe 100,000 stars at the same time and measure their brightness changes every 30 minutes to detect planets flying in front of the stars.

Kepler telescope has outstanding advantages, but its disadvantages are also very obvious. For example, it cannot obtain information on the mass of planets, and mass is very important for terrestrial planets; the universe is full of various space signals, causing the weak signals of some planets to be masked, and the Kepler telescope has difficulties in screening information; If the planet’s orbit is special and does not fly over the surface of the star, the Kepler telescope will not be able to find the planet. These factors make it difficult for the Kepler telescope to discover habitable planets. More unfortunately, in May 2013, the Kepler telescope suffered a mechanical failure and could not continue to work, resulting in the termination of this scientific research project. From start to finish, the Kepler telescope has discovered a total of about 3,300 planets outside the solar system, but they either have no liquid water or are located in an uninhabitable zone. Among them, there is no “wandering earth” that humans feel strange and familiar.

In order to find the “long-lost brother” of the Earth, Chinese astronomers have proposed a different idea-the Neighbor and Livable Planetary Survey Program, which was proposed by the Nanjing Purple Mountain Observatory of the Chinese Academy of Sciences, which can break through the noisy space signals and huge brightness differences. And the limitation of spatial resolution.

This plan is also known as the “Sound-seeking Project”. It is based on the fact that if the planet revolves around the star, it will cause the star to produce periodic small swings. By observing the subtle changes in the position of the star, the motion of the star itself is excluded It can be inferred whether there are planets around the star, and the mass of the planet can be estimated. This plan can ignore the negative effects of noisy space signals, and can also filter out giant planets like Jupiter that are mainly composed of gas.

After eight years of technological precipitation, the “Miyin Project” has now entered the implementation stage. To make “dreams shine into reality”, the measurement accuracy needs to reach micro-arc seconds, which is equivalent to observing a coin on the moon from the earth. To this end, China plans to launch a high-precision telescope for measuring celestial bodies with a measurement accuracy of the interstellar micro-arcsecond level, so that it can discover and verify habitable planets outside the solar system through direct imaging. The “small target” of this telescope is to detect about 100 stars and 50 terrestrial planets within 32 light-years of the Earth.

Nowadays, China has a deep accumulation in the observation of terrestrial planets. Relying on the rapid development of aerospace technology, it is believed that it will be able to accumulate in the search for habitable planets and live up to expectations.