Near-Earth object focused on asteroids and short-period comets. CNEOS even restricts its definition of NECs to short-period comets—, 107 such objects have been discovered. , only 20 comets have been observed to pass within of Earth, including 10 which are or have been short-period comets. Two of these comets, Halley's Comet and 73P/Schwassmann–Wachmann, have been observed during multiple close approaches. The closest observed approach was 0.0151 AU (5.88 LD) for Lexell's Comet on July 1, 1770. After an orbit change due to a close approach of Jupiter in 1779, this object is no longer a NEC. The closest approach ever observed for
Near-Earth Asteroid Scout mission researchers argue that "characterization of NEAs that are larger than 20 m in diameter is also of great relevance to inform mitigation strategies for planetary defense." The planned target, subject to change, is near-Earth object 1991 VG. 1991 VG was discovered shortly before passing just 0.003 AU from earth on 6 November 1991, and returned within 0.06 AU of Earth in August 2017. It raised interest due to the close approach, and the expectation that such an Earth-similar orbit would not have long term orbital stability. Once the flyby is complete, and if the system is still fully functioning,