Minor planet · Main belt · (87) Sylvia
87 Sylvia
A large outer-main-belt asteroid and the first asteroid found to have two moons — Romulus and Remus — making it the first known triple asteroid system.
Asteroidstriple system
Orbit & physical parameters
Osculating orbit and physical parameters from the NASA JPL Small-Body Database · Outer Main-belt Asteroid · epoch 2026-06-09 (JD 2461200.5 TDB) · Earth MOID 2.17816 au
| Semi-major axis | 3.490931 ± 5.6436e-9 au | NASA JPL · calculated |
| Eccentricity | 0.094242 ± 2.2167e-9 | NASA JPL · calculated |
| Perihelion distance | 3.161939 ± 4.9437e-9 au | NASA JPL · calculated |
| Aphelion distance | 3.819923 ± 6.1755e-9 au | NASA JPL · calculated |
| Inclination | 10.849314 ± 1.6751e-7 deg | NASA JPL · calculated |
| Longitude of ascending node | 72.945984 ± 6.1329e-7 deg | NASA JPL · calculated |
| Argument of perihelion | 267.101544 ± 1.3655e-6 deg | NASA JPL · calculated |
| Orbital period | 2,382 ± 5.7772e-6 d | NASA JPL · calculated |
| Diameter | 253.051 ± 2.953 km | NASA JPL · catalogued |
| Geometric albedo | 0.046 ± 0.004 | NASA JPL · estimated |
| Rotation period | 5.184 h | NASA JPL · catalogued |
| Absolute magnitude (H) | 6.93 mag | NASA JPL · catalogued |
Full field-level provenance
- Semi-major axis: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · orbit.elements · a · JPL orbit determination (least-squares fit to the observation arc) · calculated · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Eccentricity: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · orbit.elements · e · JPL orbit determination (least-squares fit to the observation arc) · calculated · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Perihelion distance: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · orbit.elements · q · JPL orbit determination (least-squares fit to the observation arc) · calculated · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Aphelion distance: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · orbit.elements · ad · JPL orbit determination (least-squares fit to the observation arc) · calculated · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Inclination: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · orbit.elements · i · JPL orbit determination (least-squares fit to the observation arc) · calculated · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Longitude of ascending node: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · orbit.elements · om · JPL orbit determination (least-squares fit to the observation arc) · calculated · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Argument of perihelion: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · orbit.elements · w · JPL orbit determination (least-squares fit to the observation arc) · calculated · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Orbital period: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · orbit.elements · per · JPL orbit determination (least-squares fit to the observation arc) · calculated · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Diameter: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · phys_par · phys.diameter · catalogued value · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Geometric albedo: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · phys_par · phys.albedo · Bayesian estimate · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Rotation period: Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · phys_par · phys.rot_per · catalogued value · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
- Absolute magnitude (H): Jet Propulsion Laboratory / Solar System Dynamics · JPL SBDB · phys_par · phys.H · catalogued value · JPL solution by Otto Matic, 7387 obs · retrieved 2026-07-11
Orbital elements are a calculated JPL orbit-determination fit, all referred to the single osculating epoch above (solution by Otto Matic); each carries its own uncertainty. Fields the database did not provide are omitted, never invented.
Populations
Knowledge connections
- Member of groupMain Asteroid Belt
Sources
The primary and reference sources this topic draws on.
- NASANational Aeronautics and Space Administration
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.
- NASA JPLJet Propulsion Laboratory / Solar System Dynamics
Orbital data, ephemerides, and small-body parameters for planets, asteroids, and comets.