135 Hertha

Hertha (minor planet designation: 135 Hertha) is an asteroid from the inner region of the asteroid belt, approximately 77 kilometers (48 miles) in diameter. Discovered on 18 February 1874 by German–American astronomer Christian Peters at the Litchfield Observatory near Clinton, New York,[1] it was named after the Teutonic and Scandinavian goddess of fertility, Hertha, also known as Nerthus.[2] It orbits among the Nysa asteroid family, but its classification as an metallic M-type asteroid does not match the more common F-type asteroid for this family, suggesting that it may be an interloper.[9] Spectroscopic analysis indicates the possible presence of hydrated silicates indicating that Hertha should possibly be reclassified from its present M-type to the proposed W-type.[10]

135 Hertha
Lightcurve-base 3D-model of Hertha
Discovery [1]
Discovered byC. H. F. Peters
Discovery siteLitchfield Obs.
Discovery date18 February 1874
Designations
(135) Hertha
Pronunciation/ˈhɜːrθə/
Named after
Nerthus [2]
(Norse mythology)
main-belt [1][3] · (inner)
Nysa (Hertha)[4][5]
Orbital characteristics [3]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc133.34 yr (48,701 d)
Aphelion2.9320 AU
Perihelion1.9239 AU
2.4279 AU
Eccentricity0.2076
3.78 yr (1,382 d)
233.89°
0° 15m 37.8s / day
Inclination2.3052°
343.65°
340.16°
Physical characteristics
Mean diameter
76.12 ± 3.29 km[6]
79.24±2.0 km[3]
Mass(1.21 ± 0.16) × 1018 kg[6]
Mean density
5.23 ± 0.96 g/cm3[6]
8.40061 h[7]
0.1436[3]
M[8]
8.23[1][3]

    Lightcurve data from Hertha indicates a flattened body,[7] and radar observations indicate that Hertha is non-metallic.[11] Five occultations of stars by the asteroid have been observed between 2000 and 2015.

    Discovery

    Hertha was discovered by C. H. F. Peters on 18 February 1874, in Clinton, New York.[12] Further observations were carried out in 1883 by W. T. Sampson and communicated to Astronomische Nachrichten on his behalf by Rear Admiral R. W. Shufeldt.[13]

    Physical properties

    After its discovery in 1874, subsequent observations in 1884 established Hertha's orbit. Astronomers then began investigation of its physical properties. As early as 1904, G. W. Hill reported observations of Hertha's brightness indicating a variation of half a magnitude and a short period.[14]

    In October 1992 Dotto et al. performed 20 hours of observations spread over 6 nights to investigate Hertha's rotational period, approximate shape, and the coordinates of its rotational axis. They were able to confirm a rotational period of 8.398 ± .001 hours as previously measured by Harris et al. published earlier in 1992.[8][15] In the same study, Dotto et al. measured the asteroid's shape and rotational axis. The axes' ratios were found to be: a/b = 1.34 ± .03 and b/c = 1.22 ± .05. Two possible values were determined for the rotational axis, however further measurements at different ecliptic longitudes are required to determine which is correct.[8]

    In August 2003 Torppa et al. published their results on the shape and rotational properties of a number of asteroids, including Hertha. Utilizing data from 42 lightcurves of Hertha spanning from 1978 to 2002, a more refined set of axes' ratios was obtained and a detailed shape model was obtained through inversion. New values for the axes' ratios are: a/b = 1.1 and b/c = 1.5. Measurements of the pole direction were also obtained, however like Dotto et al. they were unable to differentiate between their two possible solutions of (β=+58°, λ=96°) and (β=+53°, λ=274°).[7]

    In 2017, Hanuš et al. confirmed that the correct solution is β=53±3°, λ=277±3°. They also calculated the first non-convex shape model, based on lightcurve and stellar occultation data.[16]

    Spectral classification

    Although Hertha has long been classified as an M-type asteroid based on its spectral properties, observations carried out by Rivkin et al. in 1996 using the IRTF at Mauna Kea Observatory have raised the possibility of reclassification. The presence of a dip in the observed spectrum at 3 μm indicates that the surface is hydrated, suggesting that Hertha should be reclassified as a W-type (a "wet M-type") asteroid.[17] Based on work carried out by Salisbury and Walter, the Rivkin study estimated the water content of the asteroid to be between 0.14 and 0.27 percent by mass. This estimate is based on laboratory measurements and may not be applicable to asteroids in space.[17]

    A more recent study by Rivkin et al. published in 2002 examined the dependence of spectral absorption on the asteroid's rotational phase. The study looked at the 0.7 μm band, which is also associated with hydrated silicates, and found that the reflectance changes as the asteroid rotates, suggesting that the surface is heterogeneous with some hydrated areas intermixed with dry areas.[18]

    Asteroid family

    Hertha is one of the core members of the Nysa family (405) also known as Herta family.[4][5] The Nysa–Polana complex is the main-belt's largest grouping of asteroids with nearly 20,000 members.[19]:23

    Further reading
    • 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.
    • Hardersen, Paul S.; Gaffey, Michael J.; Abell, Paul A. (September 2006). "Near-infrared Reflectance Spectra Of 135 Hertha, 224 Oceana, 516 Amherstia, And 872 Holda". Bulletin of the American Astronomical Society. 38: 626. Bibcode:2006DPS....38.7103H.
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    gollark: Also apparently a gecko expert.

    References
    1. "135 Hertha". Minor Planet Center. Retrieved 18 September 2018.
    2. Schmadel, Lutz D. (2007). "(135) Hertha". Dictionary of Minor Planet Names – (135) Hertha. Springer Berlin Heidelberg. p. 27. doi:10.1007/978-3-540-29925-7_136. ISBN 978-3-540-00238-3.
    3. "JPL Small-Body Database Browser: 135 Hertha" (2018-05-22 last obs.). Jet Propulsion Laboratory. Retrieved 18 September 2018.
    4. "Asteroid 135 Hertha". Small Bodies Data Ferret. Retrieved 18 September 2018.
    5. "Asteroid (135) Hertha". AstDyS-2, Asteroids – Dynamic Site. Retrieved 18 September 2018.
    6. Carry, B. (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. ISSN 0032-0633. See Table 1.
    7. Torppa, J.; et al. (August 2003). "Shapes and rotational properties of thirty asteroids from photometric data". Icarus. 164 (2): 346–383. Bibcode:2003Icar..164..346T. doi:10.1016/S0019-1035(03)00146-5.
    8. Dotto, E.; et al. (October 1992). "M-type Asteroids: Rotational properties of 16 Objects". Astronomy and Astrophysics Supplement Series. 95 (2): 195–211. Bibcode:1992A&AS...95..195D.
    9. Cellino, A.; Vincenzo, Z. (October 1993). "Asteroid 'clans': Super-families or multiple events?". Celestial Mechanics and Dynamical Astronomy. 57 (1–2): 34–37. Bibcode:1993CeMDA..57...37C. doi:10.1007/BF00692459.
    10. Cellino, A.; et al. (August 2001). "The Puzzling Case of the Nysa–Polana Family". Icarus. 152 (2): 225–237. Bibcode:2001Icar..152..225C. doi:10.1006/icar.2001.6634.
    11. Shepard, M.K.; et al. (September 2006). "More Results from a Long-Term Radar Survey of M-Class Asteroids". Bulletin of the American Astronomical Society. 38: 626. Bibcode:2006DPS....38.7101S.
    12. Peters, C.A.F. (1874). "Observations of the Planet Hertha (135), made at the Litchfield Observatory of Hamilton College" (PDF). Astronomische Nachrichten. 84 (2001): 129. Bibcode:1874AN.....84..129P. doi:10.1002/asna.18740840902.
    13. Sampson, W.T.; Shufeldt, R. W. (1884). "Observations of (135) Hertha made at the Naval Observatory Washington with 9.6 inch equatorial". Astronomische Nachrichten. 107 (20): 323. Bibcode:1883AN....107..323S. doi:10.1002/asna.18841072006.
    14. Hill, G.W. (March 1904). "Variability of (135) Hertha". Astronomical Journal. 24 (557): 42. Bibcode:1904AJ.....24...42H. doi:10.1086/103543.
    15. Harris, A.W.; et al. (January 1992). "Asteroid lightcurve observations from 1981". Icarus. 95 (1): 115–147. Bibcode:1992Icar...95..115H. doi:10.1016/0019-1035(92)90195-D.
    16. Hanuš, J.; et al. (2017). "Volumes and bulk densities of forty asteroids from ADAM shape modeling". Astronomy & Astrophysics. 601: A114. arXiv:1702.01996. Bibcode:2017A&A...601A.114H. doi:10.1051/0004-6361/201629956. ISSN 0004-6361.
    17. Rivkin, A.S.; et al. (June 2000). "The Nature of M-Class Asteroids from 3-μm Observations". Icarus. 145 (2): 351–368. Bibcode:2000Icar..145..351R. doi:10.1006/icar.2000.6354.
    18. Rivkin, A.S.; et al. (March 2002). "Hydrated Minerals on Asteroids: The Astronomical Record" (PDF). Technical Report, Massachusetts Institute of Technology.
    19. Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). Identification and Dynamical Properties of Asteroid Families. Asteroids IV. pp. 297–321. arXiv:1502.01628. Bibcode:2015aste.book..297N. doi:10.2458/azu_uapress_9780816532131-ch016. ISBN 9780816532131.

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