Survey, defence and resource development of NEO

Abstract

A near-Earth object (NEO) is any small Solar system body whose orbit brings it to proximity with Earth. Currently, more than 20000 NEOs are detected, most of which have diameters less than 1 km. The study of NEOs is significant to understand the solar system. NEOs formed in the very early stage of solar system according to isotope dating, and remain most original material in proto-planetary disk. Thus, the study of NEOs can reveal the components of early solar system. Besides, NEOs are also important to explain the formation of Earth-Moon systems in giant impact hypothesis, i.e., a mar-size asteroid hit Earth 4.5 billion years ago and the fragments around Earth formed Moon via gravitational accretion. Furthermore, survey of NEOs is also important for human beings, because of the potentially hazardous objects (PHOs), which lead to the Cretaceous-Paleogene (K-Pg) extinction event, as well as the Tunguska event. Fortunately, we have lots of NEO survey programs, e.g., Catalina Sky Survey, Near-Earth Asteroid Tracking, Pan-STARRS, Zwicky Transient Facility in ground, and Near-Earth Object WISE in space with near infrared telescope, etc. These projects provide a nearly completed catalog for NEOs with diameter>1 km. We can determine the orbits of these NEOs via the astrometric time series data. However, lots of smaller NEOs with diameter <140 m are still missing, due to the detection limits of faint objects using current survey telescopes. These missing small NEOs can also lead to local destruction on Earth, e.g., the Chelyabinsk meteorite in 2013. More survey programs with larger telescopes, e.g., LSST, will be helpful to generate a more completed catalog of small NEOs and to recognize more small PHOs. After knowing the threat of PHOs, human beings need defense plans to avoid the impact or minimize the influence on human being. Although a big asteroid impact event would occur in a very low possibility, we need to take precaution. However, we do not have any feasible and effective plan to avoid the asteroid impact currently. Either nuclear explosive plan or drag the asteroid away using spacecraft engines can hardly work, Because of the huge mass (>millions tons) of the asteroid. Besides, the big fragments of the asteroid after explosion may lead to more impacts on Earth and make conditions worse. Better forethought plans need experts in astronomy, geology, life science, climatology etc., to discuss together. The NEOs may be harmful if it impacts Earth. However, the resources on asteroid, e.g., water, metal can be utilized by human beings. Utilizing the resources in space is the only way to break through the limits of Earth’s resources, and extend the footprint of human being further in space. Currently, some companies are set up and aim to mine on asteroids, e.g., the Planetary Resources Company and the Deep Space Industries. Chinese people also set up a company named Origin Space to study the plan in this field. Although, there is a long way to go, including lots of crucial techniques need to be studied, the success of development of the resources on asteroid would bring our technique and civilization in a new era.