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 Object Camera by the Spitzer Space Telescope. The spacecraft would operate in a halo orbit around the Sun–Earth , and employ a Sun shield. This orbit would allow fast data downlink speeds to Earth, allowing full-frame images to be downloaded from the telescope. Near-Earth Object Camera The Near-Earth Object Camera (NEOCam) is a proposed space-based infrared telescope designed to survey the Solar System for potentially hazardous asteroids. NEOCam would survey from the Sun–Earth Lagrange point, allowing it to look close to the Sun and see objects inside Earth's orbit. NEOCam would be a successor to the WISE mission; the principal investigator is