2021 PH27
2021 PH27 is a near-Earth asteroid of the Atira group. It was discovered by Scott Sheppard using the Dark Energy Survey's DECam imager at NOIRLab's Cerro Tololo Inter-American Observatory on 13 August 2021. 2021 PH27 has the smallest semi-major axis and shortest orbital period among all known asteroids as of 2021, with a velocity at perihelion of 106 km/s (240,000 mph). It also has the largest value of the relativistic perihelion shift, 1.6 times that of Mercury. With an absolute magnitude of 17.7, the asteroid is estimated to be larger than 1 kilometer (0.6 miles) in diameter.
Illustration showing the asteroid 2021 PH27 inside Mercury's orbit | |
| Discovery | |
|---|---|
| Discovered by | S. S. Sheppard |
| Discovery site | Cerro Tololo Obs. |
| Discovery date | 13 August 2021 |
| Designations | |
MPC designation | 2021 PH27 |
Alternative designations | v13aug1 |
Minor planet category | Atira · NEO |
| Orbital characteristics | |
| Epoch 1 July 2021 (JD 2459396.5) | |
| Uncertainty parameter 3 | |
| Observation arc | 4.15 yr (1,515 days) |
| Earliest precovery date | 16 July 2017 |
| Aphelion | 0.7903 AU |
| Perihelion | 0.1331 AU |
Semi-major axis | 0.4617 AU |
| Eccentricity | 0.7116 |
Orbital period (sidereal) | 0.31 yr (114.60 days) |
Mean anomaly | 49.496° |
Mean motion | 3° 8m 28.602s / day |
| Inclination | 31.929° |
Longitude of ascending node | 39.411° |
| 7 October 2021 @ 106 km/s | |
| 8.575° | |
| Earth MOID | 0.2251 AU |
| Mercury MOID | 0.1123 AU |
| Venus MOID | 0.0147 AU |
| Physical characteristics | |
Mean diameter | >1 km |
| 19.3 (discovery) 14 (unobservable) | |
| 17.71±0.235 | |
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