1998 KY26

 is a nearly spherical sub-kilometer asteroid, classified as a near-Earth object of the Apollo group. It measures approximately 30 m in diameter and is a fast rotator, having a rotational period of only 10.7 minutes. It was first observed on 2 June 1998, by the Spacewatch survey at Kitt Peak National Observatory during 6 days during which it passed 800,000 kilometers (half a million miles) away from Earth (a little more than twice the Earth–Moon distance).

The object's orbit is well known, since it was recovered in 2002 by the Hawaiian Observatory, and it was most recently observed, from 10 till 15 December 2020, by the Cerro Paranal. La Palma Observatory, and Mauna Kea observatories.

Orbit and classification
orbits the Sun at a distance of 1.0–1.5 AU once every 16 months (500 days). Its orbit has an eccentricity of 0.20 and an inclination of 1° with respect to the ecliptic. It has an Earth minimum orbital intersection distance of approximately 0.0025 AU, corresponding to 0.98 lunar distances.

As a result, it is one of the most easily accessible objects in the Solar System, and its orbit frequently brings it on a path very similar to the optimum Earth–Mars transfer orbit. This, coupled with its high water content, makes it an attractive target for further study and a potential source of water for future missions to Mars.

Physical properties
The physical properties of this object were measured by an international team of astronomers led by Dr. Steven J. Ostro of the Jet Propulsion Laboratory using a radar telescope in California and optical telescopes in the Czech Republic, Hawaii, Arizona and California.

is characterized as a potentially metallic X-type asteroid. Optical and radar observations indicate that it is a water-rich object.

From light curve photometry in 1998, the object is measured to have a rotation period of only 10.7 minutes, which was considered to be one of the shortest sidereal days of any known Solar System object at the time; most asteroids with established rotational rates have periods measured in hours. As a result, it cannot possibly be a rubble pile, as many asteroids are thought to be, and must instead be a monolithic object. It was the first such object to be discovered, but since 1998, several other small asteroids have been found to also have short rotation periods, some even faster than.

Exploration
In September 2020, a mission extension for JAXA's Hayabusa2 asteroid sample return probe was selected to do additional flybys of two near-Earth asteroids: in July 2026 and a rendezvous with  in July 2031. The rendezvous with will be the first visit of a rapidly rotating micro-asteroid. This will also make 1998 KY26 the smallest object to ever be studied by a spacecraft.