2017 SX17

 is a very small asteroid, classified as a near-Earth object of the Apollo group, approximately 6 - 12 m in diameter. It was first observed by astronomers of the Mount Lemmon Survey at Mount Lemmon Observatory on 29 September 2017, three days prior to its sub-lunar close encounter with Earth at 0.23 lunar distances on 2 October 2017.

Orbit and classification
is a member of the Apollo asteroids, which cross the orbit of Earth. Apollo's are the largest group of near-Earth objects with approximately 10 thousand known objects.

It orbits the Sun at a distance of 0.87–1.46 AU once every 15 months (459 days; semi-major axis of 1.16 AU). Its orbit has an eccentricity of 0.26 and an inclination of 3° with respect to the ecliptic.

The body's observation arc begins with an observation made by Pan-STARRS on 24 September 2017, five days prior to its official first observation.

Close approaches
The object last approached the Earth on 2 October 2017, at 10:20 UT, at a distance of 87065 km at a speed of 26310 km/h. This distance corresponds to 0.000582 AU.

After the 2017-flyby, it still has an exceptionally low minimum orbital intersection distance with Earth of 0.00082 AU, or 0.032 lunar distances (LD).

Physical characteristics
Based on a generic magnitude-to-diameter conversion, measures between 6 - 12 m in diameter, for an absolute magnitude of 28.3, and an assumed albedo between 0.057 and 0.24, which represent typical values for carbonaceous and stony asteroids, respectively.

As of 2018, no rotational lightcurve 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 by the Minor Planet Center.