Aten asteroid
The shortest semi-major axis for any known Aten asteroid is 0.580 AU, for object . The Aten asteroid with the smallest known perihelion is also the one with the highest known eccentricity: has an orbit with an eccentricity of 0.895, which takes it from a perihelion of 0.092 AU, well within Mercury's orbit, to an aphelion of 1.66 AU, which is greater than the semi-major axis of Mars (1.53 AU). For a brief time near the end of 2004, the asteroid 99942 Apophis (then known only by its provisional designation ) apparently posed a threat of impacting Earth in 2029 or 2036, but earlier observations were found that eliminated those possibilities.