2012 KT₄₂ is an Apollo near-Earth asteroid first observed by astronomer Alex R. Gibbs of the Mount Lemmon Survey with a 1.5-meter reflecting telescope on 28 May 2012.

The asteroid had a close approach to the Earth on 29 May 2012, approaching to only ~8950 miles (~14,440 km) above the planet's surface. This means 2012 KT₄₂ came inside the Clarke Belt of geosynchronous satellites. In May 2012, the estimated 5- to 10-metre-wide asteroid ranked #6 on the top 20 list of closest-approaches to Earth. There was no danger of a collision during the close approach. 2012 KT₄₂ passed roughly 0.01 AU (1,500,000 km; 930,000 mi) from Venus on 8 July 2012.^[1]

It is estimated that an impact would produce an upper atmosphere air burst equivalent to 11 kt TNT,^[4] roughly equal to Hiroshima's Little Boy. The asteroid would be vaporized as these small impacts occur approximately once per year. A comparable-sized object caused the Sutter's Mill meteorite in California on 2 April 2012. It was removed from the Sentry Risk Table on 30 May 2012.^[5]

• JPL Small-Body Database Browser for 2012 KT42
• 2012 KT42 - Close Approach (Remanzacco Observatory in Italy)
• Images from Flyby (spaceweather.com)
• MPEC 2012-K66 : 2012 KT42 (Minor Planet Center Discovery announcement)
• Planetary Defense Blog post on 2012 KT42
• Video: Tiny Asteroid 2012 KT42 Crossing The Sky (universetoday 29 May 2012)
• The Peculiar Flyby of Asteroid 2012 KT42 (Pasquale Tricarico : 29 May 2012)
• 2012 KT42 at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
• 2012 KT42 at ESA–space situational awareness
  • Ephemerides · Observations · Orbit · Physical properties · Summary
• 2012 KT42 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters