2017 SX₁₇ is a very small asteroid, classified as a near-Earth object of the Apollo group, approximately 6–12 meters (20–40 feet) 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.^[1][2]

2017 SX₁₇ 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.^[2]

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.^[1]

The object last approached the Earth on 2 October 2017, at 10:20 UT, at a distance of 87,065 kilometres (54,100 miles) at a speed of 26,310 km/h (16,350 mph).^[4] This distance corresponds to 0.000582 AU (0.226 LD).^[2]

After the 2017-flyby, it still has an exceptionally low minimum orbital intersection distance with Earth of 123,000 km (0.00082 AU), or 0.032 lunar distances (LD).^[2]

Based on a generic magnitude-to-diameter conversion, 2017 SX₁₇ measures between 6–12 meters (20–40 feet) 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.^[3]

As of 2018, no rotational lightcurve has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.^[2]

This minor planet has neither been numbered nor named by the Minor Planet Center.^[1]

• Bus-sized asteroid 2017 SX17 gives Earth a close shave, Skymania
• Asteroid 2017 SX17 to flyby Earth at 0.23 LD on October 2, The Watchers
• Bus-Size Asteroid Zooms by Earth in Close (But Harmless) Encounter, Space.com
• Asteroid 2017 SX17 close approach, International Asteroid Warning Network (IAWN)
• List Of Apollo Minor Planets (by designation), Minor Planet Center
• 2017 SX17 at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
• 2017 SX17 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters