In April, 2022, the press conference of "China space day" introduced the development of China's space industry. The state has approved the planetary exploration project. Following the successful completion of the first Mars exploration mission of tianwen-1, the next step of the planetary exploration project will be the exploration of asteroids. The Chinese people will go further in exploring the universe.
At present, China has begun to implement the asteroid exploration mission, and is preparing to implement the near Earth Asteroid 2016ho3 sampling return and the main belt comet 311P circling exploration mission in the asteroid belt around 2025, so as to realize the flying around detection, attachment and sampling return of near Earth Asteroids. It is hoped that three detection modes can be realized through one launch to detect two types of targets.
Asteroids (asteroids or minor planets) are similar planets in the solar system that move around the sun, but are much smaller in volume and mass than planets, including main belt asteroids, near Earth Asteroids, planetary Trojan small bodies, some extraneptune objects and some Centaur asteroids.
When people focus on the frontier issues such as whether there is water on the moon and whether Mars is suitable for human survival, asteroids should also be given corresponding attention.
On the one hand, from the perspective of safety, asteroids may bring devastating disasters. Asteroid impact may bring great disasters and even induce extinction. Asteroid impact theory is the most popular dinosaur extinction hypothesis. But so far, little is known about asteroids.
On the other hand, from a scientific point of view, asteroids may help us explore the mystery of the formation of the solar system. Because asteroids have no atmosphere, the craters and foreign elements on asteroids can be better preserved, which can be used to conduct in-depth research on the evolution of the solar system. The source of water on the earth may also be found in small planets. There are traces of water on the surface of many asteroids. Perhaps water was brought by asteroids or comets billions of years ago.
2016ho3 is an earth co orbiting celestial body, which orbits the sun and the earth at the same time. It is about 38 to 100 times the distance from the earth to the moon. It will orbit around the earth in the past 100 years or even in the next hundreds of years in the existing mode. Comet 311P is the main comet in the asteroid belt. Scientists speculate that the water on the earth may come from the watery comets in the asteroid belt. The small object exploration mission is a huge challenge, with long mission cycle and high technical difficulty. It is necessary to solve many problems, such as long-time flight of spacecraft, long-period management on the ground and long-distance communication between spacecraft and ground.
In order to comprehensively detect the rotation parameters, shape, geological morphology, surface components, magnetic field environment, etc. of asteroids, the scientific loads configured for the exploration task include the medium field of view color camera, multispectral camera, thermal radiation spectrometer, visible infrared imaging spectrometer, detection radar, magnetometer, charged particle and neutral particle analyzer, eruption analyzer, etc.
Asteroids were generally formed in the early solar system, which contains the secrets of the ancient history of the solar system. Asteroid exploration plays an indispensable role in revealing the mystery of the birth and evolution of the solar system. Precisely because the research on asteroids is so important, it has been more than 30 years since the asteroid exploration mission was formulated in China.
In 1991, the Galileo Jupiter probe launched by the United States flew over the asteroid 951 gaspa, making it the first asteroid to be closely observed. After that, the United States, Europe and Japan launched deep space exploration missions for asteroids. The mission modes are mainly divided into five types: overflight, flying around, impact, landing and return.
Table 1 basic information of some international asteroid exploration missions
At present, most of our knowledge about asteroids comes from meteorite samples, but it is difficult to determine which asteroid the meteorite samples come from. The Falcon is the world's first spacecraft to bring back material from a small planet. On may9,2003, JAXA successfully launched the Hayabusa probe. It planned to collect samples from the asteroid 25143 Itokawa and return the collected samples to the earth.
After more than two years' flight, the Falcon reached its scheduled orbit 20km away from the Tokugawa asteroid on September 12, 2005. On November 20 and 26 of the same year, the Falcon made two short landings on the Tokugawa asteroid and tried to take samples. Although both samples failed, some soil and sand splashed into the open sealed cabin during landing. Falcon collected samples from specific asteroids, bridging the gap between actual observation data and laboratory analysis.
On april25,2007, the Falcon set out on a voyage back to earth. On june13,2010, the Falcon re entered the earth's atmosphere. The re-entry module successfully landed in the desert near Woomera in southern Australia, and the main body of the probe burned up in the atmosphere.
According to JAXA, about 1500 particles from the Tokugawa asteroid were found in the re-entry capsule. On august26,2011, science magazine published 6 articles introducing the scientific achievements of the Falcon. By analyzing the collected particles, the researchers speculated that the Ogawa asteroid originated from a larger planet, and the collected particles have been exposed on the asteroid surface for about 8million years.
In order to achieve the scientific objectives, the Falcon is equipped with four scientific payloads, including visible spectrum imager (Amica), near infrared spectrometer (NIRS), optical radar (LIDAR) and X-ray spectrometer (XRS).
Table 2 scientific payload and exploration mission of Falcon (edited according to JAXA data)
After the successful completion of the Hayabusa exploration mission, JAXA launched the Hayabusa 2 probe on December 3, 2014. It plans to collect samples from the asteroid 162173 ryugu (Longgong asteroid) and return the collected samples to the earth, and then fly to the asteroid 2001 CC21 and the asteroid 1998 ky26 to carry out the next stage of exploration.
Longgong asteroid is a primitive carbonaceous near Earth Asteroid with a large number of carbonate minerals. It is considered to retain the most primitive information of the solar system, which may contain water ice, minerals, organic mixtures, etc. The study of the Longgong asteroid can gain more knowledge about the origin and evolution of planets in the solar system, especially the sources of water and organic compounds on the earth - which may be brought about by the impact of asteroids or comets on the earth, all of which are related to the origin of life on the earth.
After learning from the experience and lessons of falcon, the exploration mission of Falcon 2 is progressing smoothly. Falcon 2 took two samples respectively. For the first sampling, a tantalum bullet was shot into the surface of Longgong asteroid, and the debris on the asteroid surface was collected into the sample collector at the top of the sampling rod.
Due to the long-term space weathering of the asteroid surface, in order to determine the difference between the asteroid surface and the deep material, the second sampling of the asteroid subsurface was carried out. Falcon 2 dropped an impactor loaded with 9.5 kg of explosives on the asteroid surface. The dropped impactor detonated the explosives in mid air and hit a pure copper sheet "shell" onto the asteroid surface at high speed. The huge impact left an artificial impact crater with a diameter of more than 10 meters and a depth of about 3 meters on the asteroid surface. At the same time, in order not to be accidentally injured, Falcon 2 left a camera to monitor the explosion and impact, and took refuge in the safety zone behind the asteroid. After the dust settled, Falcon 2 began its second sampling.
On december6,2020, the sample return module successfully landed at the Woomera test site in Australia and obtained a sample with a total weight of 5.4 G. This is the first time that humans have successfully completed multiple landings on an asteroid, and it is also the first time that the subsurface samples of an asteroid have been collected. Through research, the samples of Longgong asteroid contain hydrate, a variety of organic and inorganic substances.
Falcon 2 still has about 30kg propellant left, and all systems are in good working condition. Therefore, it will continue its exploration journey. It is planned to fly over asteroid 2001 CC21 in 2026 and reach the next target asteroid 1998 ky26 in 2031.
In terms of remote sensing, the hayabusa-2 detector carries four scientific payloads (excluding those contained in the lander), including the near infrared spectrometer (nirs3), the thermal infrared imager (TIR), the optical navigation camera (ONC) and the laser altimeter (LIDAR).
Table 3 scientific load and detection task of Falcon 2 (edited according to JAXA data)
In addition to the Falcon, there are two famous asteroid probes, dawn and Osiris. On september27,2007, NASA successfully launched the dawn probe, with the purpose of traveling to the asteroid belt between Mars and Jupiter to explore the two largest protoplanets: the asteroid Vesta and the dwarf planet Ceres. Vesta is a rocky object, while Ceres is a typical ice object. These two celestial bodies were formed in the early history of the solar system. Due to the strong gravity of Jupiter, they evolved slowly and failed to become planets. By comparing the different evolution paths of these two celestial bodies, we can understand what factors control the evolution of celestial bodies. This is the first time that man has orbited the asteroid belt and visited a dwarf planet.
After about four years of flight, dawn entered the orbit of Vesta and carried out a 14 month round flight observation of Vesta. After all-round observation, scientists found that Vesta, unlike most asteroids, has formed a metal core, a rocky mantle and a shell. Data show that Vesta is also the largest single source of meteorites on earth.
Then dawn went to Ceres and arrived two and a half years later. It is found that Ceres may have ancient marine relics, and its crust may be composed of ice, salt, rock and cage hydrate. On november1,2018, NASA confirmed that dawn had run out of fuel, ending dawn's exploration journey.
Dawn is equipped with three scientific payloads to complete the detection of two celestial bodies, including framing camera (FC), visible infrared imaging spectrometer (VIR) and gamma ray and neutron detector (Grad).
Table 4 dawn scientific payload and exploration mission (edited according to NASA data)
On september8,2016, NASA successfully launched Osiris, the ongoing 1999 Bennu sampling return exploration program for asteroids. Its full name (origins spectral interpretation resource identification security regolith explorer, abbreviated as Osiris Rex) is defined in Chinese as "origin, spectral interpretation, resource identification, security, weathered layer Explorer". As the name suggests, "origin" refers to the scientific goal of studying the formation of planets and the origin of life, "spectral interpretation" refers to understanding the characteristics of asteroids through the measurement of multiple spectral bands, "resource identification" refers to identifying mineral resources according to spectral characteristics, "safety" refers to predicting the orbit of asteroids by measuring the Yarkovsky effect, so as to avoid asteroids hitting the earth, The "regolith Explorer" refers to the project goal - to retrieve regolith samples from the surface of the small planet and bring them back to earth.
The asteroid 1999 Bennu (Benu asteroid) is one of the small objects that may impact the earth and is considered as a potential threat object. Understanding the physical characteristics of Benu asteroid will help to carry out asteroid impact avoidance missions in the future. The samples collected from small planets are expected to enable scientists to further understand the formation and evolution of the solar system, including the formation of planets and the origin of life on earth.
After more than four years of flight and exploration, the sampling was successfully completed on October 20, 2020, and the samples are expected to be returned to the earth in 2023. When the sampling system comes into contact with the asteroid surface, nitrogen will be released to blow the weathered layer particles into the sampler head. In addition, the end of the sampling head also passively collects some samples.
Osiris carried six scientific payloads, including camera kit (ocams), visible infrared spectrometer (ovirs), thermal emission spectrometer (otes), weathering layer X-ray imaging spectrometer (rexis), laser altimeter (OLA) and sampling system (tagsam).
Table 5 Osiris scientific payload and exploration mission (edited according to NASA data)
April 24, 2022 is the seventh China space day and the 52nd anniversary of the successful launch of China's first man-made earth satellite, "dongfanghong-1". In these 52 years, China's space industry has created one after another remarkable Chinese miracle. We are also moving forward towards space. It is believed that in the near future, Chinese probes will also make a significant contribution to the field of planetary exploration.
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Source: National Space Science Center, Chinese Academy of Sciences, General Department of lunar and deep space exploration, Chinese Academy of Sciences