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]