132 Aethra

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132 Aethra
132Aethra (Lightcurve Inversion).png
Lightcurve-based 3D-model of Aethra
Discovery [1]
Discovered by James C. Watson
Discovery site Ann Arbor, Michigan, United States
Discovery date13 June 1873
Designations
(132) Aethra
Pronunciation /ˈiːθrə/ [2]
Named after
 Aethra
A873 LA ·A922 XB ·1949 MD ·1953 LF [3] [a]
Mars crosser
Orbital characteristics [3]
Epoch 21 November 2025 (JD 2461000.5)
Uncertainty parameter 0
Observation arc 152.30 yr (55628 d)
Aphelion 3.6230  AU (541.99  Gm)
Perihelion 1.6012 AU (239.54 Gm)
2.6121 AU (390.76 Gm)
Eccentricity 0.3870
4.2217 yr (1541.9 d)
Average orbital speed
17.72 km/s
113.0611°
0° 14m 0.24s / day
Inclination 24.9835°
258.0509°
255.6188°
Earth  MOID 0.7822 AU
Jupiter  MOID 2.2051 AU
TJupiter 3.176
Physical characteristics
42.87±1.6 km [3]
44.47±0.74 km [4]
Mass (1.59 ± 0.89/0.42)×1017 kg [4]
Mean density
3.447 ± 1.935/0.923 g/cm3 [4]
5.1684  h (0.21535  d) [3]
0.1990±0.015 [3]
M-type (Tholen)
Xe-type (Bus) [5] : 142 
8.96 [3]

    132 Aethra is a metallic asteroid and Mars-crosser on an eccentric orbit from the asteroid belt. It was discovered by James Craig Watson on 13 June 1873 in Ann Arbor, Michigan, and is the first Mars-crossing asteroid to be identified. It subsequently became a lost asteroid, and was only rediscovered in December 1922. It is named after Aethra, the mother of Theseus in Greek mythology.

    Contents

    Aethra measures approximately 43–44 kilometers in diameter and has a rotation period slightly longer than five hours. It is the largest and brightest of the Mars-crossers and is classified as an M-type asteroid under the Tholen classification scheme. Its surface is relatively reflective and is likely composed of various silicate, hydroxide, and iron-bearing minerals.

    History and naming

    Aethra was discovered by astronomer James Craig Watson on 13 June 1873 at Ann Arbor, Michigan. Its discovery, alongside that of 133 Cyrene, was announced in the journal Astronomische Nachrichten on 30 August. [6] Watson only obtained an observation arc of 22 days, insufficient to constrain its orbit very well. The usual method for calculating the orbits of asteroids discovered by Watson were inadequate due to Aethra's large orbital eccentricity, and the asteroid subsequently became lost. [7] By 1874, [8] the asteroid was named Aethra after the Greek mythological figure Aethra, mother of Theseus. [9] : 25 

    On 12 December 1922, Aethra was rediscovered as 1922 NA [7] by astronomer Benjamin Jekhowsky at Algiers Observatory. It was independently observed by G. Beljavsky on 19 December at Simeiz Observatory. Calculations of its orbit strongly indicated that it was the lost asteroid, and Aethra's recovery was announced in the journal Nature on 3 February 1923. [10] [11] In 1925, the system of provisional designation was changed to its current system. The Minor Planets Center (MPC) retroactively applied the new-style designations to those made before 1925, thus replacing 1922 NA with A922 XB. [12] [3]

    Orbit

    An orbital diagram of Aethra, with the orbits of the inner planets and the ecliptic grid shown. (132) Aethra orbit.png
    An orbital diagram of Aethra, with the orbits of the inner planets and the ecliptic grid shown.

    Aethra orbits the Sun at an average distance—its semi-major axis—of 2.61 astronomical units (AU), taking 4.22 years to complete one orbit. Due to its eccentricity of 0.39, its distance from the Sun varies from 1.60 AU at perihelion to 3.62 AU at aphelion, crossing the orbit of Mars. [3] It is the first Mars-crossing asteroid discovered. [13] : 4  Its orbital inclination is high, [7] with a value of 24.98° with respect to the ecliptic plane. [3]

    Despite crossing Mars's orbit, Aethra appears to be dynamically stable. A 2023 study by Julio Fernández and Michel Helal found that in simulations, its orbit remains stable for 2 billion years (Gyr). Aethra is protected from destabilizing close encounters with Mars by a Kozai resonance. This resonance couples variations in its perihelion distance with the precession of its argument of perihelion such that whenever its perihelion is at a minimum, it is located away from the ecliptic plane, distancing Aethra from Mars. [13] : 5  Occasionally, its perihelion is raised enough that its orbit no longer crosses Mars's. [14]

    Physical characteristics

    Aethra has an estimated diameter of 42.87 ± 1.6 kilometres (26.64 ± 0.99 mi) [3] or 44.47 ± 0.74 kilometres (27.63 ± 0.46 mi). [4] Along with its absolute magnitude of 8.96, [3] it is the largest and brightest Mars-crossing asteroid. [13] : 4  Observations of Aethra's lightcurve, or variations in its apparent brightness as it rotates, suggests a rotation period of about 5.17 hours. [3]

    Under the Tholen classification scheme, Aethra is classified as an M-type asteroid. The Bus classification scheme meanwhile classifies it as an Xe-type asteroid. [5] : 142  Aethra's geometric albedo is about 0.2, [13] : 4  and its spectrum is significantly red. Absorption features in its spectrum indicates the presence of phyllosilicate and hydroxide minerals and water ice, and the iron-rich chamosite may be the primary surface mineral on some regions on the asteroid. [15] : 1923, 1935  These features are broadly consistent with the compositions of CI and CM chondrites, but albedo and spectral slope dissimilarities rule out Aethra as a parent body of these meteorites. [15] : 1931  Variations in Aethra's spectrum seen between May and August 2008 may be caused by variable abundances of phyllosilicates or opaque surface minerals with rotation or an undiscovered moon with a distinct composition. [15] : 1923 

    Notes

    1. ↑ The MPC notates Aethra's retroactive new-style designations as 1873 LA and 1922 XB. [1]

    References

    1. 1 2 "(132) Aethra = 1873 LA = 1922 XB = 1949 MD = 1953 LF". Minor Planet Center . Retrieved 5 November 2025.
    2. ↑ Noah Webster (1884) A Practical Dictionary of the English Language
    3. 1 2 3 4 5 6 7 8 9 10 11 12 "JPL Small-Body Database Browser: 132 Aethra" (2000-06-10 last obs). Retrieved 12 May 2016.
    4. 1 2 3 4 Fienga, A.; Avdellidou, C.; Hanuš, J. (February 2020). "Asteroid masses obtained with INPOP planetary ephemerides". Monthly Notices of the Royal Astronomical Society. 492 (1): 589–602. doi: 10.1093/mnras/stz3407 . Values found in table A1.
    5. 1 2 Hardersen, Paul S.; Gaffey, Michael J.; Abell, Paul A. (May 2005). "Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroids". Icarus. 175 (1): 141–158. Bibcode:2005Icar..175..141H. doi:10.1016/j.icarus.2004.10.017.
    6. ↑ Watson, James Craig (30 August 1873). "Correspondence - Discovery of Two New Planets". Astronomical Register. 11: 284. Bibcode:1873AReg...11..284W.
    7. 1 2 3 Herget, Paul (1938). "The orbit and perturbations of (132) Aethra". Astronomical Journal. 47 (1081): 17–23. Bibcode:1938AJ.....47...17H. doi:10.1086/105455.
    8. ↑ Watson, James Craig (August 1874). "New Elements and an Ephemeris of Aethra (132)". Astronomische Nachrichten. 84: 187. Bibcode:1874AN.....84..187W.
    9. ↑ Schmadel, Lutz (2003), Dictionary of minor planet names, vol. 1, Springer, p. 68, ISBN   9783540002383.
    10. ↑ "Lost Planet Recovered". Nature. 111 (2779): 159. 3 February 1923. doi:10.1038/111159a0.
    11. ↑ "Report Lost Planet of 1873 Found Again; Algerian and Simeis Astronomers Locate Aethra, First Sighted by Prof. Watson of Ann Arbor". New York Times. 3 February 1923. Retrieved 5 November 2025.
    12. ↑ "Provisional Designations". Minor Planets Center. Retrieved 5 November 2025.
    13. 1 2 3 4 Fernández, Julio A.; Helal, Michel (April 2023). "On the observed excess of large Mars-crossers in high-inclination orbits". Icarus. 394. Bibcode:2023Icar..39415398F. doi:10.1016/j.icarus.2022.115398. 115398.
    14. ↑ JeongAhn, Youngmin; Malhotra, Renu (December 2015). "The current impact flux on Mars and its seasonal variation". Icarus. 262: 140–153. arXiv: 1503.03885 . Bibcode:2015Icar..262..140J. doi:10.1016/j.icarus.2015.08.032.
    15. 1 2 3 Hardersen, Paul S.; Cloutis, Edward A.; Reddy, Vishnu; Mothé-Diniz, Thais; Emery, Joshua P. (14 November 2011). "The M-⁄ X-asteroid menagerie: Results of an NIR spectral survey of 45 main-belt asteroids". Meteoritics and Planetary Science. 46 (12): 1910–1938. doi: 10.1111/j.1945-5100.2011.01304.x .
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