Millions of small rocky bodies called asteroids are present in the solar system. If the asteroid were "bright", we would see as much as stars in the night sky. A significant portion of them circulate in a ring between the orbits of Mars and Jupiter, between 2 and 4 AU, called the asteroid belt. It thus marks the boundary between the terrestrial planets and the gas giants. An asteroid is a celestial object in the solar system, not visible to the naked eye because of its small size, which varies from a few tens of meters to several hundred kilometers in diameter. Objects less than 50 m in diameter are called meteorites. Asteroids are remnants of the protoplanetary disk that failed to gather enough to form a planet during their formation. Asteroids are of great importance in understanding the formation of the solar system, it is for this reason that astronomers show a strong interest in the study of these objects. Since February 2011, the NEOWISE NASA mission dedicated to research in the infrared small body, completed its quest on asteroids and comets in our solar system. NEOWISE discovered 20 comets, more than 33,000 asteroids in the main belt between Mars and Jupiter, and 134 near-Earth objects (NEOs). NEOs are asteroids and comets with orbits less than 1.3 AU, i.e. they can come within 45 million km from Earth orbit. The new model represents the coverage of NEOs is shown on the left of the image. It can thus be compared to the old model, which estimates the visible were higher. Observations NEOWISE reduce by 40%, the actual number of near-Earth asteroids that exceed 100 meters.
Image: Representation of the inner solar system where each red dot represents one asteroid. Of course the sizes of objects are not to scale. The infrared observations of NEOWISE are more precise than those obtained previously in visible light because asteroids of the same size emit substantially the same amount of infrared radiation, so they reflect a highly variable amount of visible light according to their albedo. The results of NEOWISE allow requalify the number of asteroids of significant size from 35 000 to 19 500, however, the majority of objects remains yet to be discovered.