 A deconvolved image of 13 Egeria by VLT/SPHERE | |
| Discovery[1] | |
|---|---|
| Discovered by | Annibale de Gasparis |
| Discovery site | Naples Obs. |
| Discovery date | 2 November 1850 |
| Designations | |
| (13) Egeria | |
| Pronunciation | /ɪˈdʒɪəriə/[2] |
Named after | Egeria |
| 1850 VA | |
| Main belt | |
| Adjectives | Egerian |
| Symbol | .svg) (historical).svg) (historical, variant) |
| Orbital characteristics[3] | |
| Epoch 17.0 October 2024 (JD 2460600.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 63566 days (174.03 yr) |
| Aphelion | 2.79788AU |
| Perihelion | 2.35759 AU |
| 2.57774 AU | |
| Eccentricity | 0.085403 |
| 4.14yr (1511.7d) | |
Averageorbital speed | 18.56 km/s |
| 305.547° | |
| 0° 14m 17.34s / day | |
| Inclination | 16.532° |
| 43.208° | |
| 79.222° | |
| Earth MOID | 1.43636 AU |
| Jupiter MOID | 2.35842 AU |
| TJupiter | 3.363 |
| Physical characteristics | |
| Dimensions | 214.8 km × 192 km[4] 238 km × 199 km × 182 km (±12 km × 11 km × 10 km)[5] |
| 202±3 km[5] 207.6 ± 8.3 km (IRAS)[3] | |
| Flattening | 0.24[a] |
| Mass | (9.2±2.1)×1018 kg[5] (15.9±4.4)×1018 kg[b][6] |
Meandensity | 2.13±0.49 g/cm3[5] 3.4±1.0 g/cm3[6] |
Equatorialsurface gravity | ≈0.0580 m/s2 |
Equatorialescape velocity | ≈0.1098 km/s |
| 7.045 h[3] 7.046664±0.000003 h[5] | |
| 59°[5] | |
| 38°±5°[5] | |
| 31°±5°[5] | |
| 0.087[5] 0.049 ± 0.028[3] 0.085 ± 0.007[7] | |
| Temperature | ~174K |
| G-type asteroid[3] | |
| 9.71 to 12.46[8] | |
| 6.91[3] 6.74[5] | |
13 Egeria is a largemain-beltG-type asteroid.[9] It was discovered byAnnibale de Gasparis on 2 November 1850. Egeria was named byUrbain Le Verrier, whose computations led to the discovery ofNeptune, after the mythological nymphEgeria ofAricia, Italy, the wife ofNuma Pompilius, second king of Rome.[10]
Egeria was discovered on the evening of 2 November 1850 by Italian astronomerAnnibale de Gasparis at theAstronomical Observatory of Capodimonte.[11][12]: 128 Whereas de Gasparis's previous two discoveries—10 Hygiea and11 Parthenope—were identified by comparison with theBerlin Academy star charts, Egeria was identified using his own ecliptic charts intended for finding new celestial objects.[13]: 119 [12]: 128 Egeria's discovery was announced in December 1850 by astronomerBenjamin A. Gould throughThe Astronomical Journal.[14] Following the discovery, de Gasparis delegated the naming rights of the asteroid toUrbain Le Verrier. Le Verrier chose to name the asteroid afterEgeria, a mythologicalnymph and councillor ofNuma Pompilius.[12]: 128
Upon its discovery, both de Gasparis and Gould labelled Egeria as a new planet.[11][14] However, by the mid-1800s, the classification and terminology of the asteroids were quickly evolving.[15] Soon after Egeria's discovery, other astronomers described it as an "asteroid"[16] or a "minor planet".[17]: 25 Throughout the latter half of the 19th century, the terms "asteroid" and "minor planet" became favored,[15] although some publications continued to label Egeria and other asteroids as planets.[15][18]: 42
In 1851, de Gasparis announced his chosensymbol for Egeria—that of a buckler. However, Gould had apparently not seen the announcement, and in an 1852 table of asteroid symbols he left Egeria's blank.[19]: 8 [16] No mention of a star was made, though in 1852John Russell Hind included one in his drawn symbol for Egeria:.svg)
(U+1CEC6 inUnicode 17.0). The symbol is sometimes depicted with a round form (),[19]: 8 though only Hind's form was encoded.[20] As the number of asteroids assigned a symbol grew in number through the mid-1800s, the practicality of assigning each a unique astronomical symbol was questioned. In 1851, astronomerJohann Franz Encke proposed an alternative system of a number—denoting the object's order of discovery—inscribed in a circle. For Egeria, this would be ⑬.[15][16] This system was quickly adopted by astronomers, though eventually astronomers switched from an inscribed circle to parentheses and eventually a bare number[15]—hence(13) Egeria or13 Egeria in modern notation.[1][3]
Egeria orbits the Sun at an average distance—itssemi-major axis—of 2.58astronomical units (AU), placing it within themain asteroid belt and near the 3:1mean-motion resonance withJupiter.[3][21]: 323 Along its orbit, its distance from the Sun varies between 2.36 AU atperihelion to 2.80 AU ataphelion due to itsorbital eccentricity of 0.09. Its orbit isinclined by 16.5° with respect to theecliptic, and it takes 4.14 years to complete one orbit.[3] Egeria is classified as abackground asteroid, as it does not belong to anasteroid family.[22]
Egeriaocculted a star on 8 January 1992. Its disc was determined to be quite circular (217×196 km). On 22 January 2008, it occulted another star, and this occultation was timed by several observers inNew Mexico andArizona, coordinated by the IOTA Asteroid Occultation Program.[4] The result showed that Egeria presented an approximately circular profile to Earth of 214.8×192 km, well in agreement with the 1992 occultation.[citation needed] It has also been studied byradar.[23]
In 1988 a search for satellites or dust orbiting this asteroid was performed using theUH88 telescope at theMauna Kea Observatories, but the effort came up empty.[24] Spectral analysis of Egeria shows it to be unusually high in water content, 10.5–11.5% water by mass.[25]
.png)
{{cite web}}:|archive-url= is malformed: timestamp (help)CS1 maint: url-status (link){{cite book}}:ISBN / Date incompatibility (help){{cite web}}: CS1 maint: url-status (link){{cite journal}}: CS1 maint: multiple names: authors list (link)