Astronomy:13 Egeria

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13 Egeria Astronomical symbol of 13 Egeria (historical)
24px (historical, variant)
A deconvolved image of 13 Egeria by VLT/SPHERE
Discovery[1]
Discovered byAnnibale de Gasparis
Discovery siteNaples Obs.
Discovery date2 November 1850
Designations
(13) Egeria
Pronunciation/ɪˈdʒɪəriə/[2]
Named afterEgeria
1850 VA
Minor planet categoryMain belt
AdjectivesEgerian
Orbital characteristics[3]
Epoch 17.0 October 2024 (JD 2460600.5)
Uncertainty parameter 0
Observation arc63566 days (174.03 yr)
|{{{apsis}}}|helion}}2.79788 astronomical unit|AU (418.557 Gm)
|{{{apsis}}}|helion}}2.35759 AU (352.690 Gm)
2.57774 AU (385.624 Gm)
Eccentricity0.085403
Orbital period4.14 yr (1511.7 d)
Average Orbital speed18.56 km/s
Mean anomaly305.547°
Mean motion0° 14m 17.34s / day
Inclination16.532°
Longitude of ascending node43.208°
79.222°
Earth MOID1.43636 AU (214.876 Gm)
Jupiter MOID2.35842 AU (352.815 Gm)
TJupiter3.363
Physical characteristics
Dimensions214.8 km × 192 km[4]
238 km × 199 km × 182 km (± 12 km × 11 km × 10 km)[5]
Mean diameter202±3 km[5]
207.6 ± 8.3 km (IRAS)[3]
Flattening0.24[lower-alpha 1]
Mass(9.2±2.1)×1018 kg[5]
(15.9±4.4)×1018 kg[lower-alpha 2][6]
Mean density2.13±0.49 g/cm3[5]
3.4±1.0 g/cm3[6]
Equatorial surface gravity
≈0.0580 m/s2
Equatorial escape velocity
≈0.1098 km/s
Rotation period7.045 h[3]
7.046664±0.000003 h[5]
Axial tilt59°[5]
Pole ecliptic latitude31°±5°[5]
Pole ecliptic longitude38°±5°[5]
Geometric albedo0.087[5]
0.049 ± 0.028[3]
0.085 ± 0.007[7]
Physics~174 K
G-type asteroid[3]
Apparent magnitude9.71 to 12.46[8]
Absolute magnitude (H)6.91[3]
6.74[5]


13 Egeria is a large main-belt G-type asteroid.[9] It was discovered by Annibale de Gasparis on 2 November 1850. Egeria was named by Urbain Le Verrier, whose computations led to the discovery of Neptune, after the mythological nymph Egeria of Aricia, Italy, the wife of Numa Pompilius, second king of Rome.[10]

History

Egeria was discovered on the evening of 2 November 1850 by Italian astronomer Annibale de Gasparis at the Astronomical Observatory of Capodimonte.[11][12]: 128  Whereas de Gasparis's previous two discoveries—10 Hygiea and 11 Parthenope—were identified by comparison with the Berlin 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 astronomer Benjamin A. Gould through the Astronomical Journal.[14] Following the discovery, de Gasparis delegated the naming rights of the asteroid to Urbain Le Verrier. Le Verrier chose to name the asteroid after Egeria, a mythological nymph and councillor of Numa 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 chosen symbol 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 1852 John Russell Hind included one in his drawn symbol for Egeria: 15px (U+1CEC6 𜻆 in Unicode 17.0). The symbol is sometimes depicted with a round form (15px),[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, astronomer Johann 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 or 13 Egeria in modern notation.[1][3]

Physical properties

OCCULT4 visualization of 13 Egeria occultation event of January 22, 2008

Egeria occulted a star on January 8, 1992. Its disc was determined to be quite circular (217×196 km). On January 22, 2008, it occulted another star, and this occultation was timed by several observers in New Mexico and Arizona, 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. It has also been studied by radar.[21]

In 1988 a search for satellites or dust orbiting this asteroid was performed using the UH88 telescope at the Mauna Kea Observatories, but the effort came up empty.[22] Spectral analysis of Egeria shows it to be unusually high in water content, 10.5–11.5% water by mass.[23]

A three-dimensional model of 13 Egeria based on its light curve

See also

Notes

  1. ↑ Flattening derived from the maximum aspect ratio (c/a): f=1−ca, where (c/a) = 0.76±0.06.[5]
  2. ↑ (8.0±2.2)×10−12 M☉

References

  1. ↑ 1.0 1.1 "(13) Egeria = 1850 VA". Minor Planet Center. https://www.minorplanetcenter.net/db_search/show_object?utf8=%E2%9C%93&object_id=13. Retrieved 8 September 2025. 
  2. ↑ Noah Webster (1884) A Practical Dictionary of the English Language
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 "JPL Small-Body Database Browser: 13 Egeria". http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=13. Retrieved 21 December 2024. 
  4. ↑ 4.0 4.1 Timerson, Brad. "IOTA Asteroid Occultation Results for 2008". http://www.asteroidoccultation.com/observations/Results/Data2008/20080122_EgeriaProfile.png. Retrieved 2010-01-19. 
  5. ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 Vernazza, P. (October 2021). "VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis". Astronomy and Astrophysics 654: A56. doi:10.1051/0004-6361/202141781. A56. Bibcode: 2021A&A...654A..56V. 
  6. ↑ 6.0 6.1 James Baer, Steven Chesley & Robert Matson (2011) "Astrometric masses of 26 asteroids and observations on asteroid porosity." The Astronomical Journal, Volume 141, Number 5
  7. ↑ "Asteroid Data Archive". Planetary Science Institute. http://www.psi.edu/pds/archive/astdata04/simps04/diamalb.tab. Retrieved 2008-11-03. 
  8. ↑ apmag 9.71 (2061-Nov-06) to 12.46 (1990-Mar-12) JPL Horizons daily output for 1950 to 2099
  9. ↑ Rivkin, A. S.; J. K. Davies. "High-resolution 2.5–3.5 Template:MuM Observations of C-, B- and G-class asteroids.". http://www.lpi.usra.edu/meetings/LPSC98/pdf/1310.pdf. Retrieved 2008-04-20. 
  10. ↑ Schmadel, Lutz D. (2003). Dictionary of minor planet names. 1 (5th ed.). Berlin Heidelberg New York: Springer-Verlag. pp. 16. ISBN 3-540-00238-3. 
  11. ↑ 11.0 11.1 de Gasparis, Annibale (November 1850). "Account of discovery of Egeria, November 2, 1850". Monthly Notices of the Royal Astronomical Society 11: 1. doi:10.1093/mnras/11.1.1. Bibcode: 1850MNRAS..11....1D. 
  12. ↑ 12.0 12.1 12.2 Hind, John Russell (1852). "Chapter VIII. The Minor or Ultra-Zodiacal Planets." (in en). The Solar System: Descriptive Treatise Upon the Sun, Moon, and Planets, Including an Account of All the Recent Discoveries. New York, United States: G. P. Putnam's Sons. p. 126. https://archive.org/details/solarsystemdescr00hind/page/126/mode/2up. 
  13. ↑ Airy, G. B. (February 1851). "Address on presenting the medal to Dr. A. de Gasparis". Monthly Notices of the Royal Astronomical Society 11: 116–120. doi:10.1093/mnras/11.4.116. Bibcode: 1851MNRAS..11..116A. 
  14. ↑ 14.0 14.1 Gould, B. A. (6 December 1850). "New planet (13) Egeria". Astronomical Journal 1 (20): 158. doi:10.1086/100108. Bibcode: 1850AJ......1..158G. 
  15. ↑ 15.0 15.1 15.2 15.3 15.4 Hilton, J. L. (16 November 2007). "When did asteroids become minor planets?". U.S. Naval Observatory. http://aa.usno.navy.mil/faq/docs/minorplanets.php. Retrieved 27 March 2025. 
  16. ↑ 16.0 16.1 16.2 Gould, B. A. (January 1852). "On the symbolic notation of the asteroids". The Astronomical Journal 2: 80. doi:10.1086/100212. Bibcode: 1852AJ......2...80G. https://articles.adsabs.harvard.edu/pdf/1852AJ......2...80G. 
  17. ↑ Hind, John Russel (1852). An Astronomical Vocabulary: Being an Explanation of All Terms in Use Amongst Astronomers at the Present Day. John W. Parker and Son. ISBN 978-1120148056. 
  18. ↑ Airy, George Biddell (1869). "Horizontal and Vertical Diameters and Right Ascensions and North Polar Distances of the Sun, Moon and Planets, Deduced from the Observations, and Compared with the Nautical Almanac". Greenwich Observations in Astronomy, Magnetism and Meteorology Made at the Royal Observatory. 2 29: D31–D63. Bibcode: 1869GOAMM..29D..31A. 
  19. ↑ 19.0 19.1 Bala, Gavin Jared; Miller, Kirk (18 September 2023). "Unicode request for historical asteroid symbols". Unicode. https://www.unicode.org/L2/L2023/23207-historical-asteroids.pdf. Retrieved 26 September 2023. 
  20. ↑ "Miscellaneous Symbols Supplement". The Unicode Consortium. 2025. https://www.unicode.org/charts/PDF/U1CEC0.pdf. 
  21. ↑ "Radar-Detected Asteroids and Comets". NASA/JPL Asteroid Radar Research. http://echo.jpl.nasa.gov/asteroids/. Retrieved 2011-10-30. 
  22. ↑ Gradie, J.; Flynn, L. (March 1988), "A Search for Satellites and Dust Belts Around Asteroids: Negative Results", Abstracts of the Lunar and Planetary Science Conference 19: pp. 405–406, Bibcode: 1988LPI....19..405G. 
  23. ↑ Rivkin, A. S.; Davies, J. K. (2002). "Calculated water concentrations on C-class asteroids". Lunar and Planetary Science (XXXIII): 1414. Bibcode: 2002LPI....33.1414R. https://www.lpi.usra.edu/meetings/lpsc2002/pdf/1414.pdf. 



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