 VLT-SPHERE image of Euphrosyne,deconvolved with the MISTRAL algorithm. | |
| Discovery | |
|---|---|
| Discovered by | J. Ferguson |
| Discovery date | September 1, 1854 |
| Designations | |
| (31) Euphrosyne | |
| Pronunciation | /juːˈfrɒsɪniː/[1] |
Named after | ΕὐφροσύνηEyphrosynē |
| A907 GP; A918 GB | |
| Main belt | |
| Adjectives | Euphrosynean/juːfrɒsɪˈniːən/[2] |
| Orbital characteristics[3] | |
| Epoch April 27, 2019 (JD 2458600.5) | |
| Aphelion | 3.8523 AU (576.296 Gm) |
| Perihelion | 2.4585 AU (367.786 Gm) |
| 3.1554AU (472.041 Gm) | |
| Eccentricity | 0.2209 |
| 5.61yr (2041.585 d) | |
| 87.1671° | |
| Inclination | 26.3033° |
| 31.1186° | |
| 61.4704° | |
| Knownsatellites | 1 |
| Physical characteristics | |
| Dimensions | (294±6) × (280±10) × (248±6) km[4] |
| 268±4 km[5] 267.1±2.6 km(IRAS)[3] 268±6 km[4] | |
| Flattening | 0.14[a] |
| Mass | (16.5±2.6)×1018 kg[5] (17±3)×1018 kg[4] |
Meandensity | 1.64±0.27 g/cm3[5] 1.66±0.24 g/cm3[4] |
| 0.230400 d (5.529595 h)[4] | |
| 0.05[5] 0.0543[6] | |
| C[3][7] | |
| 10.16[8] to 13.61 | |
| 6.86[3] | |
31 Euphrosyne is one of thelargest asteroids (approximately tied for 7th place, to within measurement uncertainties). It was discovered byJames Ferguson on September 1, 1854, the first asteroid found from North America. It is named afterEuphrosyne, one of theCharites inGreek mythology. In 2019 a smallcompanion was discovered. It is the third-roundest known asteroid (after1 Ceres and10 Hygiea); this is thought to be due to having re-accreted after being disrupted by a collision, and it is not close to hydrostatic equilibrium.[4]
Euphrosyne is a fairly dark body near the belt's outer edge. Consequently, it is never visible with binoculars, having a maximumapparent magnitude at the best possible opposition of around +10.2 (as in November 2011), which is fainter than any of the thirty asteroids previously discovered.[9]
Euphrosyne has a highorbital inclination and eccentricity having nodes near perihelion and aphelion, Euphrosyne's perihelion lies at the northernmost point of its orbit. During perihelic oppositions, Euphrosyne is very high in the sky from northern latitudes and invisible from southern countries such as New Zealand and Chile.
Euphrosyne is aC-type asteroid with a primitive surface possibly covered by thick ejecta blanket from the collision that created its moon and collisional family. There are no deep basins. Any craters larger than 40 km in diameter must have flat floors to not be visible in the VLT images, consistent with an icy C-type composition. The lack of craters could also be due to the young age of the surface.[4]
The discovery of its satellite enabled the first accurate measure of Euphrosyne's mass in 2020, at(1.7±0.3)×1019 kg, and thus a density of1.7±0.2 g/cm3. The low density suggests that Euphrosyne is half water ice if internal porosity is 20%.[4]
Euphrosyne is the namesake of a complexfamily of about two thousand asteroids that share similar spectral properties andorbital elements. They are thought to have arisen from a recent collision approximately 280 million years ago.[4] All members have relatively high orbital inclinations.[10] The second largest body in this group,895 Helio, is most likely an interloper.[11]
| Discovery | |
|---|---|
| Discovery date | 2019 March 15 |
| Orbital characteristics[4] | |
| Epoch EQJ2000 | |
| 672±12 km | |
| Eccentricity | 0.043+0.041 −0.014 |
| 1.209±0.001 days | |
| Inclination | 1.4°±0.5° |
| 80.1°±9.3° | |
| 135.2°±13.5° | |
| Physical characteristics | |
| 4.0±1.0 km | |
In 2019 a small satellite was discovered, likely resulting from the same collisional event that created the family. Preliminary orbit computations indicated an orbital period of approximately 1.2 days and a semi-major axis of 670 km. VLT images indicate that the moon is 4 km in diameter, assuming it has the same albedo as Euphrosyne.[4]
