Dimorphos
Dimorphos is the small moon of asteroid Didymos, about 190 × 150 × 120 m, and the first world whose orbit people have changed on purpose. On 26 September 2022, at 23:14:24 UTC, NASA's DART spacecraft struck it at about 6.1 km/s. Its orbit around Didymos, 11 hours 55 minutes before the impact, settled at about 11 hours 22 minutes after it — 33 minutes shorter.
Key facts
Science
Physical
- Mean radius
- 0.0746 km
- JPL Horizons — DART post-impact reconstruction, solution s547 (Naidu et al. 2024, Planet. Sci. J. 5, 74)
Orbit around (65803) Didymos
- Distance from (65803) Didymos
- 1.15 km
- From JPL orbital elements
- Orbital period
- 11.47 hours
- From JPL's reconstruction of the DART impact (Horizons)
- Eccentricity
- 0.02762
- From JPL's reconstruction of the DART impact (Horizons)
- Inclination to (65803) Didymos's Laplace plane
- 0.00 °
- From JPL's reconstruction of the DART impact (Horizons) · The Laplace plane is the one a moon's orbit precesses about: close in it is the planet's equatorial plane, the plane of the rings, and further out it tilts toward the planet's own orbit.
Rotation
- Rotation period
- 11.37 hours
- Tidal locking
- Tidally locked to its parent
Composition
- Bulk composition
- A rubble pile of boulders and gravel with no bare bedrock seen, most likely the same stony rock as Didymos, from which it probably formed. DART's camera saw it up close only in the last minutes before the impact. Its mass has not been measured on its own: the published figure assumes it is as dense as Didymos, so no mass, density or surface gravity is shown here.
Radiation & temperature
- Insolation
- 0.517 S⊕ · 52% of the sunlight Earth receives
- Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
Discovery & history
- Discovered
- November 20, 2003
- By
- Petr Pravec and colleagues (Ondřejov Observatory)
- Name
- Greek for 'having two forms' — named by the IAU on 23 June 2020 at the suggestion of planetary scientist Kleomenis Tsiganis, because it would be known in two forms: before DART's impact and after it.
Found on 20 November 2003 by Petr Pravec and colleagues at Ondřejov Observatory, from regular dips in Didymos's brightness as the moon passed in front of it and behind it; Arecibo radar images showed it three days later. It was known only as S/2003 (65803) 1 until 2020. The first and only close look came from DART's own camera, in the final minutes before the impact.
Watched DART's impact from 58 km (57.7 km in JPL's reconstruction), returning 426 images of it and its plume.
Images
Images from open archives · credit shown per image