 Lightcurve-based 3D-model of Massalia | |
| Discovery[1] | |
|---|---|
| Discovered by | A. de Gasparis |
| Discovery site | Naples Obs. |
| Discovery date | 19 September 1852, 04:31 |
| Designations | |
| (20) Massalia | |
| Pronunciation | /mæˈseɪliə/[2] |
Named after | Marseille(French city)[3] |
| Massilia/mæˈsɪliə/[4] | |
| main belt[1][5] · Massalia[6] | |
| Adjectives | Massalian/mæˈseɪliən/[2] |
| Orbital characteristics[5] | |
| Epoch 23 March 2018 (JD 2458200.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 164.08yr (59,929 d) |
| Aphelion | 2.7514AU |
| Perihelion | 2.0662 AU |
| 2.4088 AU | |
| Eccentricity | 0.1422 |
| 3.74 yr (1,366 d) | |
| 12.443° | |
| 0° 15m 48.96s / day | |
| Inclination | 0.7087° |
| 206.11° | |
| 2021-Nov-04 | |
| 256.58° | |
| Physical characteristics | |
| Dimensions | 160×145×132 km[7] 160×145×130 km[8] |
| 145.50±9.3 km[9] | |
| Mass | 5.2×1018 kg[10] 5.67×1018 kg[7] |
Meandensity | 3.54±0.85 g/cm3[7] |
| 8.098 h[11] | |
| 0.210[9] | |
| Tholen =S[5] SMASS =S[5] | |
| 8.3[12] to 12.0 | |
| 6.50[5][11] | |
| 0.186" to 0.058" | |
20 Massalia is a stonyasteroid and the parent body of theMassalia family located in the inner region of theasteroid belt, approximately 145 kilometers (90 miles) in diameter. Discovered by Italian astronomerAnnibale de Gasparis on 19 September 1852, it was named for the Latin name of the French city ofMarseille, from which the independent discoverJean Chacornac sighted it the following night.[3] It was the first asteroid that was not assigned an iconic symbol by its discoverer.[13]
It came toopposition 179 degrees from the Sun on 16 June 2023,[14] and came toaphelion (farthest distance from the Sun) on 17 September 2023.[needs update]
Massalia is the namesake and theparent body of theMassalia family (404), a very large inner beltasteroid family consisting ofstony asteroids with very low inclinations.[6][15]: 23 It is by far the largest body in this family. The remaining family members are fragments ejected by a cratering event on Massalia.[16]
It orbits the Sun in theinner main-belt at a distance of 2.1–2.8 AU once every 3 years and 9 months (1,366 days;semi-major axis of 2.41 AU). Its orbit has aneccentricity of 0.14 and aninclination of 1° with respect to theecliptic.[5]
Massalia has an above-average density for S-type asteroids, similar to the density ofsilicate rocks. As such, it appears to be a solid unfractured body, a rarity among asteroids of its size. Apart from the few largest bodies over 400 km in diameter, such as1 Ceres and4 Vesta, most asteroids appear to have been significantly fractured, or are evenrubble piles. In 1998, Bange estimated Massalia to have a mass of 5.2×1018 kg assuming that 4 Vesta has 1.35×10−10solar mass.[10] The calculation of the mass of Massalia is dependent on the mass of 4 Vesta andperturbation of44 Nysa.[10]
Light curve analysis indicates that Massalia's pole points towardsecliptic coordinates either (β, λ) = (45°, 10°) or (β, λ) = (45°, 190°) with a 10° uncertainty.[8] This gives anaxial tilt of 45° in both cases. The shape reconstruction from light curves has been described as quite spherical with large planar, nonconvex parts of the surface.
In 1988 there was a search for satellites or dust orbiting this asteroid using theUH88 telescope at theMauna Kea Observatories, but none were found.[17]
In February 2024, water molecules were discovered on 20 Massalia, alongside7 Iris, marking the first time water molecules were detected on asteroids.[18][19]
Massalia was discovered on 19 September 1852, byAnnibale de Gasparis atNaples Observatory in Italy, and also found independently the next night byJean Chacornac atMarseilles Observatory, France. It was Chacornac's discovery that was announced first. In the nineteenth century the variant spellingMassilia was often used. Asteroids discovered prior to Massalia were assignediconic symbols, like the ones traditionally used to designate the planets. However, astronomers had begun to phase out this practice with the discovery of16 Psyche in March 1852, and 20 Massalia (being the first object in the Solar System with a non-mythological name)[3] was the first asteroid that was not assigned an iconic symbol.
