99942 Apophis is a near-Earth asteroid with a diameter of 370 metres that caused a brief period of concern in December 2004 when initial observations indicated a probability up to 2.7% that it would hit Earth or Moon on April 13, 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth or the Moon in 2029. However, until 2006, a possibility remained that during the 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole, a small region no more than about 800 metres (1⁄2 mi) in diameter, that would set up a future impact exactly seven years later on April 13, 2036. Image credit: Astronomical Institute of the Charles University: Josef Ďurech, Vojtěch Sidorin

Related channels: ASTEROIDS, HAYABUSA (JAXA SPACECRAFT), DAWN (NASA SPACECRAFT), DWARF PLANETS, OSIRIS REX (NASA SPACECRAFT)