At 1:31 am on May 29, 2025, the Long March 3B Y110 carrier rocket lifted the Tianwen-2 probe from the Xichang Satellite Launch Center into the sky. The detector accurately entered the predetermined orbit, embarking on a ten-year journey of scientific exploration. What will Tianwen-2's ten-year space journey bring back? What scientific foundation will exploring small celestial bodies in the solar system lay for China's deep space exploration? Today we will talk about it. The Tianwen-2 mission is not the second Mars exploration mission after Tianwen-1, but an important component of China's planetary exploration project. The mission aims to achieve scientific exploration of two small celestial bodies in the solar system, the near Earth asteroid 2016 HO3 and the main belt comet 311P/PanSTARRS (hereinafter referred to as 311P), through a single launch. In summary, this trip is "one round trip plus one one-way trip". After the launch of Tianwen-2 into orbit, it will take one year to fly to its first target: the near Earth asteroid 2016 HO3. The orbital period of this asteroid around the Sun is 365.77 days, which is very close to Earth's 365.25 days. It's difficult to shake off a car that's driving at the same speed on the highway, and the same goes for the solar system. So, the near Earth asteroid 2016 HO3 will maintain a distance of 38 to 100 Earth Moon distances from Earth for the next 300 years, constantly following the Earth around. Being closer to Earth means that this asteroid is easier to reach than other celestial bodies in the solar system, and also implies that it has a deep connection to the origin and evolution of Earth. For example, it could be the "shrinking" of the Earth or a byproduct of the formation of the Earth Moon system. After reaching the near Earth asteroid 2016 HO3, Tianwen-2 will accompany it for one year at a distance of approximately 20 kilometers. During this period, following the principle of "flying while exploring, gradually approaching", it carried out close range detection tasks while selecting suitable landing sampling points. Afterwards, the probe will gradually land on the surface of the asteroid from a parking point 3 kilometers away, collecting samples of over 100 grams of the asteroid. Next, the probe will return to its anchorage and take over six months to return to Earth. However, this return is "passing through the house without entering": Tianwen-2 will put down a "passenger" - the asteroid sample return capsule, which will be taken over by ground researchers. The probe's main body will use the Earth's gravity acceleration and be driven by the ion electric propulsion system to quickly reach its next destination, the main belt comet 311P. This journey is very long, and the probe will need to fly for about 7 years to reach it. Then, it will accompany and conduct close range scientific exploration at a distance of 20 kilometers from the target until the end of the mission. Comet 311P is located approximately 330 million kilometers from the Sun in the asteroid rich region between the orbits of Mars and Jupiter, known as the 'main belt'. In 2013, scientists discovered that this small celestial body had six comet like tails, which raised many interesting questions. For example, is this small celestial body a native of the main belt or an outsider? If it was born here and grew here, how did volatile substances survive so close to the sun to this day? Is this preservation mechanism universal? What is the state of a comet during its "hibernation" period? Did the water that formed the Earth's primitive oceans contribute to the formation of main belt asteroids? It can be said that scientists have high hopes for the detection results of comet 311P in the main belt. Further observations on Earth have indicated that comet 311P in the main belt may have another satellite, providing additional research value for Tianwen-2's exploration mission and bringing more technical challenges. The research direction of small celestial bodies is that both of the exploration targets of the Half Day Question 2 spacecraft are small celestial bodies in the solar system. The exploration and research of small celestial bodies can be divided into two main aspects: the origin and evolution of the solar system, and the impact of small celestial bodies on the Earth. Small celestial bodies have always been an important research object in the field of the origin and evolution of the solar system. Small celestial bodies are one of the earliest formed celestial bodies in the solar system, each orbiting the sun for billions of years in a dull and uninteresting manner. Compared with large planets, these primitive celestial bodies have undergone the least changes in their physical and chemical properties after formation, retaining a large amount of evidence from the early formation of the solar system. Before the development of aerospace technology, the only way for humans to study small celestial bodies up close was through meteorites. About 80% of meteorites are primitive chondrites, formed in the early solar system 4.5 billion years ago, which relatively fully preserves the history of condensation, fractionation, and evolution of the solar system's protoplanetary disks. There are also a few meteorites that are iron meteorites, stony iron meteorites, or non chondrite meteorites, which are products of melting differentiation and undergo a process of crystallization after the melting of various components. Their formation period was also in the early solar system 4.5 billion years ago, but the molten structure tells a different story: these meteorites were once inside certain asteroids and were part of high-temperature cores or mantle. So, why did some asteroids undergo melting and differentiation in the early solar system, while others did not experience this geological process? What is the physical mechanism behind melt differentiation? What are the distribution patterns in time and space within the solar system? Are the numerous small celestial bodies in the asteroid belt formed by the rupture of protoplanets from large planets, or are they unable to condense into large planets due to various reasons and retain their small celestial body forms? Behind many issues, there may be clues to the origin and evolution of the solar system. There are two research directions regarding the impact of small celestial bodies on Earth: one is joy and the other is worry. The research in the Joy direction is that at the beginning of Earth's formation, it was a hot and dry rocky planet, and the water in the primitive ocean was likely brought about by the impact of a large number of water containing small celestial bodies, providing key conditions for the growth of life on Earth. International research on meteorite and asteroid samples has also discovered a variety of organic compounds, including aromatic hydrocarbons, carboxylic acids, sulfonic acids, fullerenes, fatty hydrocarbons, purines, pyrimidines, and dozens of amino acids, providing new ideas for the origin of life on Earth. The research on the direction of concern is the disaster brought by asteroid impact events to life on Earth. The famous dinosaur extinction event goes without saying. The Tunguska explosion at the beginning of the last century was the first alarm bell of the era of scientific prosperity. Even the probability event of asteroid 2024 YR4 colliding with Earth at the beginning of this year shocked everyone. The orbit of small celestial bodies is easily influenced by various factors, including their shape, density, material distribution, rotation rate, axis orientation, and surface temperature changes, in addition to gravitational disturbances from other celestial bodies. Understanding the impact of these factors on the orbital evolution of small celestial bodies is the foundation for predicting and responding to the risk of small celestial body impacts. This time, Tianwen-2 was equipped with 10 scientific payloads and 1 payload to conduct a comprehensive investigation of two small celestial bodies from the surface to the interior. These loads mainly have the following investigation contents and scientific purposes. 1. Conduct research on the morphology and orbital dynamics of small celestial bodies using a medium field of view color camera, narrow field of view navigation sensor, and laser integrated navigation sensor, including measuring the relative orbit between the small celestial body and the detector, constructing a fine three-dimensional model and local terrain data of the sampling area, measuring the basic physical characteristics such as the shape, size, and rotation parameters of the small celestial body. 2. The "physical" thermal radiation spectrometer, visible infrared imaging spectrometer, and multispectral camera of small celestial bodies are used to establish surface temperature distribution maps and thermal inertia distribution maps from multiple bands, collect surface spectral data for studying the material composition of small celestial bodies, and a rotating diffraction hyperspectral camera (equipped with a payload) is also involved in this research. In addition, detection radar is used to understand the layered structure of the surface and subsurface of small celestial bodies, and to conduct research on the internal structure of small celestial bodies. 3. The task of "living" conditions for small celestial bodies is divided into multiple parts: magnetometers collect information on remanence, magnetization strength, and charge characteristics; The charged particle and neutral particle analyzer measures parameters such as solar wind flux distribution, temperature, density, velocity, as well as neutral gas composition and density distribution near the main belt comet; The ejecta analyzer measures the physical properties, composition, content, and spatial distribution characteristics of dust particles, used to study the space environment of small celestial bodies and the possible presence of ejecta. The innovative sampling technology to cope with the unknown landing situation of Tianwen-2 space exploration's first station near Earth asteroid 2016 HO3 sampling work is the top priority and the most difficult level of the entire exploration mission. The surface of small celestial bodies presents difficulties such as weak gravity, irregularity, and unknown material properties, which pose risks of rebound, tilting, poor medium adaptation, and inability to sample during probe landing, and increase the difficulty of return. Scientists currently know very little about this asteroid, and can only roughly estimate its size from its brightness to be between 40 to 100 meters, about the size of an ordinary office building. Such a small celestial body has a surface gravity of only one millionth that of Earth, so it's more accurate to say that the probe is "attached" rather than "falling". In addition, it is necessary to guard against the active impact of small celestial bodies on the detector. Because this asteroid rotates quite quickly, it can complete one revolution in 28 minutes. If it were a sphere with a diameter of 60 meters, its equatorial rotation speed would be 11 centimeters per second, which may exceed the surface escape velocity of the asteroid. At this point, if the probe lands recklessly, it is easy to be swept away by its rugged surface and hit back into space. Therefore, Tianwen-2 has made many innovations in technology. Tianwen-2 has designed three sampling modes for possible scenarios: hover, touch, and attachment. Taking the attachment mode as an example, the core components of the attachment sampling robot include a multi joint robotic arm and an attachment sampler. Four robotic arms are distributed around the periphery of the detector, each with four joints that fold normally and unfold before landing. The end of the robotic arm is equipped with an attached sampler, which has both attachment fixation and sampling functions. That is to say, each robotic arm has a mouth in its palm. The top of the detector is equipped with a pressure engine, which can provide a pressing force during landing to prevent the detector from rebounding, and provide drilling pressure for the attached sampler to "bite" in after landing. At the same time, each robotic arm can sense the contact force between the attached sampler and the asteroid surface in real time, and dissipate the impact on land through joint reverse drive, just like how we bend our legs to buffer when jumping from a high place, achieving active soft landing. The lateral landing speed of Tianwen-2 is designed to be less than 5 centimeters per second. For the previously assumed "60 meter diameter sphere", it is expected to choose a high latitude landing (where the star catalog speed is lower) and strive to match the rotation of the asteroid to avoid the risk of lateral impact. The attached sampling robot can also achieve multi-point detection by crawling on the surface of asteroids through gait coordination between robotic arms and multiple attachments of the attached sampler. After successful attachment, sampling becomes easier. The internal design of the attached sampler includes an ultrasonic drilling mechanism and a grinding and cleaning mechanism. The former can drill holes on the surface of asteroids to form mechanical connections, while the latter can collect samples generated by drilling. The grinding and cleaning mechanism can also use grinding wheels and brushes to grind and sample the entire hard attachment area. In short, Tianwen-2 does face some unique difficulties, such as the smallest sampled celestial body to date, the weakest gravity, and the fastest rotation speed. The ingenious ideas of technology workers will ultimately be validated by the actual performance of detectors. The Tianwen-2 mission is the first asteroid exploration mission carried out by China to build the basic engineering capability for solar system exploration, and its targets were two poorly known celestial bodies from the beginning