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
Campo Imperatore Near-Earth Object Survey choose targets that cannot be done elsewhere very easily during the epoch of the observing run. Campo Imperatore Near-Earth Object Survey The CINEOS program (Campo Imperatore Near-Earth Object Survey), started in 2001, is dedicated to the discovery and follow-up of near-Earth objects (NEOs), namely asteroids and comets which periodically approach or intersect the Earth's orbit. In particular CINEOS is addressed to the discovery of Atens and Interior-Earth Objects (IEOs) by extending survey coverage at small solar elongations, and to the discovery of the other kind of NEOs by observing with longer exposures (up to a limiting magnitude of 21) in