Eos (minor planet designation: 221 Eos) is a large main-belt asteroid that was discovered by Austrian astronomer Johann Palisa on January 18, 1882, in Vienna. In 1884, it was named after Eos, the Greek goddess of the dawn, to honour the opening of a new observatory that was hoped to bring about a new dawn for Viennese astronomy.[5]

221 Eos
Discovered byJohann Palisa
Discovery date18 January 1882
(221) Eos
Named after
A882 BA
Main belt (Eos)
AdjectivesEoan /ˈ.ən/[2]
Orbital characteristics[3]
Epoch 31 July 2016 (JD 2457600.5)
Uncertainty parameter 0
Observation arc130.21 yr (47561 d)
Aphelion3.3249 AU (497.40 Gm)
Perihelion2.69594 AU (403.307 Gm)
3.01044 AU (450.355 Gm)
5.22 yr (1907.8 d)
17.16 km/s
0° 11m 19.284s / day
Physical characteristics
Dimensions103.87±3.6 km[3]
103.52 ± 5.60 km[4]
Mass(5.87 ± 0.34) × 1018 kg[4]
Mean density
10.10 ± 1.74 g/cm3[4]
10.443 h (0.4351 d)

The asteroid is orbiting the Sun with a semimajor axis of 3.01 AU, a period of 5.22 years, and an eccentricity of 0.1. The orbital plane is inclined by 10.9° to the plane of the ecliptic. It has a mean cross-section of 104 km,[3] and is spinning with a rotation period of 10.4 hours. Based upon its spectral characteristics, this object is classified as a K-type asteroid. The orbital properties show it to be a member of the extensive Eos asteroid family, which is named after it.[6] The spectral properties of the asteroid suggest it may have come from a partially differentiated parent body.[7]


  1. ^ Noah Webster (1884) A Practical Dictionary of the English Language
  2. ^ "Eoan". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  3. ^ a b c "221 Eos". JPL Small-Body Database. NASA/Jet Propulsion Laboratory. Archived from the original on 13 September 2020. Retrieved 12 May 2016.
  4. ^ a b c Carry, B. (December 2012), "Density of asteroids", Planetary and Space Science, 73 (1): 98–118, arXiv:1203.4336, Bibcode:2012P&SS...73...98C, doi:10.1016/j.pss.2012.03.009. See Table 1.
  5. ^ Schmadel, Lutz (2003), Dictionary of Minor Planet Names, Springer Science & Business Media, p. 35, ISBN 9783540002383.
  6. ^ Veeder, G. J.; et al. (March 1995), "Eos, Koronis, and Maria family asteroids: Infrared (JHK) photometry", Icarus, 114 (1): 186–196, Bibcode:1995Icar..114..186V, CiteSeerX, doi:10.1006/icar.1995.1053.
  7. ^ Mothé-Diniz, T.; Carvano, J. M. (November 2005), "221 Eos: a remnant of a partially differentiated parent body?", Astronomy and Astrophysics, 442 (2): 727–729, Bibcode:2005A&A...442..727M, doi:10.1051/0004-6361:20053551.

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