What is Near Earth object (NEO) info Chemical Man

A near-Earth object (NEO) is any small Solar System body whose orbit can bring it into proximity with Earth. By definition, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). If a NEO's orbit crosses the Earth's and the object is larger than 140 meters (460 ft) across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids.

Known NEOs include more than seventeen thousand near-Earth asteroids (NEAs), more than one hundred short-period near-Earth comets (NECs), and a number of solar-orbiting spacecraft and meteoroids, large enough to be tracked in space before striking the Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the Earth. NEOs have become of increased interest since the 1980s because of greater awareness of the potential danger some of the asteroids or comets pose, and methods of mitigation are being researched.

Based on the orbit calculations of NEOs, the risk of future impacts is assessed on two scales, the Torino scale and the more complex Palermo scale, both of which rate a risk of any significance with values above 0. Some NEOs have had positive initial Torino or Palermo scale ratings after their discovery, but as of March 2018, more precise calculations based on subsequent observations led to a reduction of the rating to or below 0 in all cases.

Since 1998, the United States, the European Union, and other nations are scanning for NEOs in an effort called Spaceguard. The initial aim of cataloging at least 90% of NEOs that are at least 1 kilometer (km) wide—about 0.62 miles (mi), which would cause a global catastrophe in case on an impact on Earth—had been met by 2011. In later years, the survey effort has been expanded[9] to objects as small as about 140 m (460 ft) across, which still have potential for large-scale, though not global, damage.

Due to their Earth-like orbits and low surface gravity, NEOs are easy targets for spacecraft. As of March 2018, five near-Earth comets and three near-Earth asteroids have been visited by spacecraft, and probes are en route to two more NEAs. Plans to mine NEAs commercially have been picked up by a private company.