15 Eunomia

Stony main-belt asteroid October 2019 yes #D6D6D6 15 Eunomia 15 Eunomia VLT (2021), deconvolved.pdf VLT-SPHERE image of Eunomia Annibale de Gasparis Naples Obs. 29 July 1851 (15) Eunomia j uː ˈ n oʊ m i əNoah Webster (1884) A Practical Dictionary of the English Language Eunomia Main belt Eunomia family Eunomian j uː ˈ n oʊ m i ə nEunomian 24px|class=skin-invert|𜻈 (historical) 21 November 2025 (JD 2461000.5) 0 174.18 yr 3.13834 AU 2.14603 AU 2.64219 AU 0.187781 4.29490 yr (1568.71 d) 113.726° 11.7614° 292.881° 98.5072° 2.4255 AU 3.340 2.64357 0.14887 13.109° 42.698 -52.044 340 x 248 x 229 km (± 14 x 13 x 14 km)18 270 3 km6 0.47Flattening derived from the maximum aspect ratio (c/a): , where (c/a) = 0.53 0.02.6 3.119 0.024 19 kg (2025)14Calculated from its standard gravitational parameter GM = 2.082 0.016 km3 s2.3.026 0.093 0.101 19 kg (2022)8Siltala and Granvik reported Eunomia's mass as 1.522 0.047 0.051 -11 Solar masses (), where 1 is 1.988 30 kg 3.03 0.10 g/cm314 6.083 h (0.2535 d) 355 2 °18 -70 2 °18 -11 ° to orbit (retrograde)18 S-type asteroidU−B=0.451 0.019B−V=0.839 0.015 7.9 to 11.24 5.41 0.18760.248 0.0420.163 0.030 0.29 to 0.085 15 Eunomia is a large asteroid in the middle asteroid belt. It is the largest of the stony (S-type) asteroids, with a mean diameter of about 270 km mi. It is between the eight and twelfth largest main belt asteroid, containing about 1% of its mass. It was discovered on 29 July 1851 by astronomer Annibale de Gasparis, who chose to name the asteroid after the Greek goddess Eunomia. It is elongated and irregular in shape, and rotates once every six hours and five minutes. Eunomia is the largest member of the Eunomia family, one of the largest known asteroid families in the main belt. Asteroids of the Eunomia family share orbital and compositional similarities to Eunomia itself. History Discovery Eunomia was discovered by Italian astronomer Annibale de Gasparis on the night of 29 July 1851 at Naples Observatory in Naples, Italy. There, while observing around the 18th hour of right ascension just below the ecliptic, he spotted a starlike object with a magnitude of 9.130 Though the object's low position in the sky prevented de Gasparis from observing it as thoroughly,130 he concluded that it was a "new planet" and reported his discovery in a letter to A.C. Petersen in Altona, Germany. Petersen in turn announced de Gasparis's discovery in the journal Astronomische Nachrichten on 22 August 1851. Naming and symbol De Gasparis selected the name Eunomia after Eunomia of Greek mythology, who was one of the Horae and the personification of law and order.14 He described its symbol as a star above a heart: 12px|class=skin-invert|alt=15 Eunomia symbol (U+1CEC8 𜻈 in Unicode 17.0).3, 8 Orbit Eunomia orbits the Sun at an average distance—its semi-major axis—of 2.64 astronomical units (AU), taking 4.29 Earth years to complete one revolution. It is located in the middle main asteroid belt, and its orbit is inclined by 11.8° with respect to the ecliptic. Due to its orbital eccentricity of 0.19, its distance from the Sun ranges from 2.15 AU at perihelion to 3.14 AU at aphelion. Eunomia family Eunomia family Eunomia is the largest member of the Eunomia family, comprising an estimated ~70% of its mass.73 The Eunomia family is one of the largest asteroid families known, with 13099 identified members.452 It occupies the middle main belt, with an outer boundary at the 8:3 mean-motion resonance with Jupiter and an inner boundary at a series of secular resonances.1153 Its members orbit with relatively high eccentricities and inclinations.446 Most members are stony S-type asteroids,452 though A-type asteroids are more common than average in the family.1 Around 20% of asteroids located within the Eunomia family region are spectrally dissimilar interlopers. Most of these interlopers belong to the overlapping Adeona family, whose namesake is the C-type asteroid 145 Adeona.584 Rotation Eunomia has a sidereal day of 6 hours and 5 minutes, which was determined from analyzing its lightcurve, or variations in its observed brightness. It has retrograde spin (clockwise when viewed from north of the ecliptic), rotating in the opposite direction compared to Earth.453 Its north pole is pointed towards the ecliptic south, with an axial tilt of 20° relative to its orbit (11° to its orbital plane).18 Physical characteristics Eunomia is the largest and most massive S-type asteroid,18 with a volume-equivalent mean diameter of 270 km mi and an estimated mass of about 3e19 kg lb.68 Eunomia is between the eighth and twelfth largest asteroid in the main belt and contains about 1% of its mass.8 It has an estimated density of about 3 g/cm3.14 It is elongated, irregular,737 and egg-shaped, with a pointed end and a blunted end.453 Spectrum and composition Eunomia is classified as a stony S-type asteroid,1 the second-most common asteroid spectral type. In Michael Gaffey's classification scheme, Eunomia is an S(III)-type, implying the presence of calcium-rich pyroxenes on its surface. Mineralogical studies using astronomical spectroscopy identified the presence of olivine, troilite, and iron–nickel alloy.453 Its surface is compositionally uneven: the pointed end has olivine and a mineralogy similar to stony-iron meteorites, while the blunt end has iron-rich pyroxenes and basalt.446 The variability of Eunomia's surface mineralogy may be a sign that it underwent partial planetary differentiation in its past. The overabundance of A-type asteroids in its family additionally support partial or complete differentiation.1 See also Former classification of planets Notes References (15) Eunomia = 1851 OA https://minorplanetcenter.net/db_search/show_object?object_id=15 Minor Planet Center 2026-05-18 5 February 2026 https://web.archive.org/web/20260205121630/https://minorplanetcenter.net/db_search/show_object?object_id=15 live (5060 obs) 2025-11-07 last obs. JPL Small-Body Database Lookup: 15 Eunomia (A851 OA) https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=15 Jet Propulsion Laboratory 2026-05-18 15 November 2020 https://web.archive.org/web/20201115003118/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=54087809;cad=1#/?sstr=15 live SsoCard https://ssp.imcce.fr/forms/ssocard/ Institut de mécanique céleste et de calcul des éphémérides 22 May 2026 A. C. Petersen Planeten-Circular de 1851-08-22 Astronomische Nachrichten 33 2 31–32 10.1002/asna.18520330211 The Solar System: Descriptive Treatise Upon the Sun, Moon, and Planets, Including an Account of All the Recent Discoveries en Chapter VIII. The Minor or Ultra-Zodiacal Planets. https://archive.org/details/solarsystemdescr00hind/page/126/mode/2up John Russell Hind John Russell Hind 1852 126 G. P. Putnam's Sons New York, United States Donald H. Menzel Jay M. Pasachoff amp 1983 A Field Guide to the Stars and Planets 2nd Houghton Mifflin 391 Boston, MA 0-395-34835-8 registration https://archive.org/details/fieldguidetostar00menz_0/page/391 Reed Kevin L. Michael J. Gaffey Gaffey Michael J. Lebofsky Larry A. Shape and Albedo Variations of Asteroid 15 Eunomia Icarus 1997 125 2 446 10.1006/icar.1996.5627 1997Icar..125..446R https://ui.adsabs.harvard.edu/abs/1997Icar..125..446R/abstract 18 April 2022 6 September 2021 https://web.archive.org/web/20220418230639/https://ui.adsabs.harvard.edu/abs/1997Icar..125..446R/abstract live https://www.sciencedirect.com/science/article/abs/pii/S0019103599961481 10.1006/icar.1999.6148 On the Size Distribution of Asteroid Families: The Role of Geometry 1999 Tanga P. Cellino A. Michel P. Zappalà V. Paolicchi P. Dell'Oro A. Icarus 141 1 65–78 1999Icar..141...65T subscription 5 February 2021 6 September 2021 https://web.archive.org/web/20210205200041/https://www.sciencedirect.com/science/article/abs/pii/S0019103599961481 live Lazzaro D December 1999 The Eunomia Family: A Visible Spectroscopic Survey https://linkinghub.elsevier.com/retrieve/pii/S0019103599962139 Icarus en 142 2 445–453 10.1006/icar.1999.6213 1999Icar..142..445L 25 July 2024 22 May 2026 https://web.archive.org/web/20240725183402/https://linkinghub.elsevier.com/retrieve/pii/S0019103599962139 live subscription 10.1051/0004-6361:20030032 Paolo Tanga Tanga Paolo Asteroid observations with the Hubble Space Telescope FGS Astronomy & Astrophysics 2003 401 2 733–741 2003A&A...401..733T 8977642 free Schmadel Lutz D. Dictionary of minor planet names 1 5th 2003 Springer-Verlag Berlin Heidelberg New York 3-540-00238-3 16 10.1007/978-3-540-29925-7_13 Nathues Andreas Mottola Stefano Kaasalainen Mikko Neukum Gerhard June 2005 Spectral study of the Eunomia asteroid family https://linkinghub.elsevier.com/retrieve/pii/S0019103504004312 Icarus en 175 2 452–463 10.1016/j.icarus.2004.12.013 4 December 2024 22 May 2026 https://web.archive.org/web/20241204121045/https://linkinghub.elsevier.com/retrieve/pii/S0019103504004312 live subscription Carruba V. Michtchenko T. A. December 2007 A frequency approach to identifying asteroid families http://www.aanda.org/10.1051/0004-6361:20077689 Astronomy & Astrophysics 475 3 1145–1158 10.1051/0004-6361:20077689 free 2007A&A...475.1145C 0004-6361 Radović Viktor Novaković Bojan Carruba Valerio Marčeta Dušan September 2017 An automatic approach to exclude interlopers from asteroid families https://academic.oup.com/mnras/article/470/1/576/3850232 Monthly Notices of the Royal Astronomical Society en 470 1 576–591 10.1093/mnras/stx1273 free 0035-8711 1705.09226 Pitjeva E. V. Elena V. Pitjeva Masses of the Main asteroid Belt and the Kuiper Belt from the Motions of Planets and Spacecraft Solar System Research 44 8–9 554–566 2018 1811.05191 10.1134/S1063773718090050 2018AstL...44..554P 119404378 etal P. Vernazza M. Ferrais L. Jorda J. Hanuš B. Carry M. Marsset VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis Astronomy & Astrophysics 654 A56 free 10.1051/0004-6361/202141781 October 2021 A56 2021A&A...654A..56V 239104699 10261/263281 free Siltala L. Granvik M. February 2022 Masses, bulk densities, and macroporosities of asteroids (15) Eunomia, (29) Amphitrite, (52) Europa, and (445) Edna based on Gaia astrometry https://www.aanda.org/10.1051/0004-6361/202141459 Astronomy & Astrophysics 658 A65 10.1051/0004-6361/202141459 free 2111.06700 2022A&A...658A..65S 0004-6361 https://www.unicode.org/L2/L2023/23207-historical-asteroids.pdf Unicode request for historical asteroid symbols Bala Gavin Jared Miller Kirk 18 September 2023 unicode.org Unicode 26 September 2023 26 September 2023 https://web.archive.org/web/20230926074401/https://www.unicode.org/L2/L2023/23207-historical-asteroids.pdf live December 2024 Asteroid Eunomia at opposition, December 2024 https://www.skyatnightmagazine.com/advice/asteroid-eunomia-december-2024 2026-05-22 BBC Sky at Night Magazine en 8 March 2026 https://web.archive.org/web/20260308161229/https://www.skyatnightmagazine.com/advice/asteroid-eunomia-december-2024 live Howells Kate What are asteroids made of? https://www.planetary.org/articles/what-are-asteroids-made-of 2024-06-18 2026-05-22 The Planetary Society en 20 April 2026 https://web.archive.org/web/20260420101111/https://www.planetary.org/articles/what-are-asteroids-made-of live Fuentes-Muñoz Oscar Farnocchia Davide Giorgini Jon D. Park Ryan S. 2025-12-01 Asteroid Mass Estimation by Mutual Perturbations During Close Encounters After Gaia Focused Product Release The Astronomical Journal 170 6 353 10.3847/1538-3881/ae0cc9 0004-6256 free 2025AJ....170..353F 283347135 Phua Yu Yu de Kleer Katherine Butler Bryan Cambioni Saverio Shepard Michael February 2026 Thermophysical Modeling of Asteroid (15) Eunomia from Spatially Resolved ALMA and VLA Data The Planetary Science Journal 7 2 47 10.3847/PSJ/ae3751 free 2026PSJ.....7...47P 2632-3338 Nesvorný David 2026-03-23 A Census before Rubin of Asteroid Families in the Main Belt The Astrophysical Journal Supplement Series 283 2 63 10.3847/1538-4365/ae4bd4 free 2602.20382 2026ApJS..283...63N 0067-0049 External links shape model deduced from lightcurve, including composition variations across the surface Elements and Ephemeris for (15) Eunomia Minor Planet Center http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=b2011&o=00015 26 May 2011 dead https://web.archive.org/web/20160303231732/http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=b2011&o=00015 3 March 2016 (displays Elong from Sun and V mag for 2011) 15 14 Irene 15 16 Psyche Category:Eunomia asteroids Eunomia Eunomia Category:S-type asteroids (Tholen) Category:S-type asteroids (SMASS) 18510729