2017 XO2

, also written 2017 XO2, is a sub-kilometer asteroid and near-Earth object of the Apollo group approximately 110 m in diameter. The asteroid was discovered by Pan-STARRS in December 2017, after it already had approached Earth at 0.051 AU or 20 lunar distances (LD) on 6 November 2017. On 26 April 2057, it will pass Earth at a similar distance of 21 LD again.

Discovery and observations
was discovered by Pan-STARRS at Haleakala Observatory, Hawaii, on 10 December 2017, when the asteroid was about 0.3 AU from Earth and had a solar elongation of 125°.

On 20 January 2018 with a 40-day observation arc, it reached Torino scale 1 with an estimated 1 in 3000 chance of impacting Earth on 28 April 2057. The nominal JPL Horizons 28 April 2057 Earth distance was estimated at 0.001 AU with a 3-sigma uncertainty of ±52 million km. NEODyS listed the nominal 28 April 2057 Earth distance at 0.03 AU. A Monte Carlo simulation using Solex 12 with 1000 clones of the asteroid generated one impactor.

On 27 January 2018 Pan-STARRS precovery images from November and December 2011 were announced, and  was removed from the Sentry Risk Table. These precovery images extended the observation arc from 40 days to 6.21 years. It is now known that on 26 April 2057 the asteroid will be just past closest approach roughly 0.056 AU from Earth with a 3-sigma uncertainty of ±3000 km.

The asteroid was last observed on 20 January 2018 at apparent magnitude 24 by T14 Mauna Kea. As the asteroid is becoming very faint, further observations during this approach are difficult. The next good chance to recover the asteroid will be between March and late April 2022 when the asteroid will pass about 0.0544 AU from Earth.

Orbit and classification
is an Apollo asteroid, the largest group of near-Earth objects and Earth-crossing asteroids with approximately 10 thousand known members. It orbits the Sun at a distance of 0.72–1.55 AU once every 15 months (440 days; semi-major axis of 1.13 AU). Its orbit has an eccentricity of 0.36 and an inclination of 15° with respect to the ecliptic. The asteroid has a notably low minimum orbital intersection distance with Earth of 0.00027 AU, or 0.11 LD.

Physical characteristics
On the Sentry Risk Table, the object had an estimated mean diameter of 110 m. Based on a generic magnitude-to-diameter conversion, measures between 100 and 200 meters in diameter, for an absolute magnitude of 22.4, and an assumed albedo between 0.05 and 0.20, which represent typical values for carbonaceous and stony asteroids, respectively. As of 2018, no rotational lightcurve of this object has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.

Numbering and naming
This minor planet has neither been numbered nor named.