(10503) Johnmarks Main-belt Asteroid
Discovered on 27 September 1987 by H. Debehogne at La Silla.
John Marks (b. 1943) founded the international non-profit organization Search for Common Ground (SFCG) in 1982 and served as its President until 2014; he is now a Senior Advisor. SFCG is dedicated to seeking peaceful resolutions for conflicts via exchange visits and other person-to-person interactions.Naming citation (WGSBN Bull. 2, #3, 5), IAU / Minor Planet Center, via NASA/JPL
Where Johnmarks is today
Seen from above the solar system on 2026-10-14: Johnmarks is 2.35 au from the Sun and 2.63 au from Earth. Computed from JPL's orbital elements.
Facts
| Number | 10503 |
| Provisional designation | 1987 SG13 |
| Orbit class | Main-belt Asteroid |
| Diameter | 3.97 km (#12,812 largest of 17,440 named asteroids with a measured size) |
| Albedo | 0.213 |
| Rotation period | 5.30 hours |
| Absolute magnitude (H) | 14.28 |
| Orbital period | 3.31 years |
| Semi-major axis | 2.22 au |
| Perihelion – aphelion | 1.97 – 2.48 au |
| Eccentricity | 0.114 |
| Inclination | 4.71° |
| Closest distance between its orbit and Earth's (MOID) | 0.978 au |
Data: NASA/JPL Small-Body Database and the IAU Minor Planet Center.
Also named after someone called John
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