2020 SW
2020 SW is a tiny near-Earth asteroid discovered by the Mount Lemmon Survey on 18 September 2020, six days before it made its closest approach to Earth. The asteroid passed within 21,600 kilometres (13,400 mi) from Earth's surface on 24 September 2020 11:13 UT, within the geostationary altitude of 36,000 kilometres (22,000 mi). The encounter with Earth perturbed the asteroid's heliocentric trajectory from an Apollo-type orbit to an Aten-type orbit with a semi-major axis within one astronomical unit from the Sun. As a result, the asteroid will not make any close approaches to Earth within 0.01 astronomical units (4 LD) in the next 200 years.
| Discovery | |
|---|---|
| Discovered by | Mt. Lemmon Survey (Kacper W. Wierzchoś) |
| Discovery site | Mt. Lemmon Obs. |
| Discovery date | 18 September 2020 |
| Designations | |
MPC designation | 2020 SW |
Alternative designations | C378AD2 |
Minor planet category | NEO · Apollo (pre-flyby) Aten (post-flyby) |
| Orbital characteristics | |
| Epoch 17 December 2020 (JD 2459200.5) | |
| Uncertainty parameter 5 | |
| Observation arc | 6 days |
| Aphelion | 1.140 AU |
| Perihelion | 0.7425 AU |
Semi-major axis | 0.941 AU |
| Eccentricity | 0.21118 |
Orbital period (sidereal) | 0.91 yr |
Mean anomaly | 353.718° |
Mean motion | 1° 4m 45.117s / day |
| Inclination | 2.326° |
Longitude of ascending node | 1.808° |
| 22 December 2020 19:43 UT | |
| 118.950° | |
| Earth MOID | 0.00042 AU (63,000 km) |
| Physical characteristics | |
Mean diameter | 4–9 m (assumed albedo 0.05–0.25) |
Synodic rotation period | 0.0079039±0.0000001 h (28.4540±0.0004 s) |
| 21.4 (at discovery) | |
| 29.063±0.335 29.06 | |
With an estimated diameter roughly 4–9 metres (13–30 ft) across, 2020 SW is comparable to the size of a small school bus. Had it impacted Earth, it would mostly have disintegrated as a fireball during atmospheric entry and might have left a common strewn field. Extensive observations of its brightness during the close encounter show that it is an elongated body with a rapid rotation period of 28.5 seconds.