115 Thyra

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115 Thyra
115Thyra (Lightcurve Inversion).png
A three-dimensional model of 115 Thyra based on its light curve.
Discovered by James Craig Watson
Discovery date 6 August 1871
MPC designation (115) Thyra
Pronunciation /ˈθrə/
Named after
Main belt
Orbital characteristics[1]
Epoch 31 July 2016 (JD 2457600.5)
Uncertainty parameter 0
Observation arc 143.31 yr (52344 d)
Aphelion 2.8376 AU (424.50 Gm)
Perihelion 1.92394 AU (287.817 Gm)
2.38077 AU (356.158 Gm)
Eccentricity 0.19188
3.67 yr (1341.8 d)
19.13 km/s
0° 16m 5.88s / day
Inclination 11.595°
Earth MOID 0.97246 AU (145.478 Gm)
Jupiter MOID 2.63437 AU (394.096 Gm)
TJupiter 3.486
Physical characteristics
Dimensions 79.83±1.4 km[1]
79.83 km[2]
Mass 5.3×1017 kg
Equatorial surface gravity
0.0223 m/s²
Equatorial escape velocity
0.0422 km/s
7.241 h (0.3017 d)
Temperature ~180 K

115 Thyra is a fairly large and bright inner main-belt asteroid that was discovered by Canadian-American astronomer J. C. Watson on August 6, 1871[4] and was named for Thyra, the consort of King Gorm the Old of Denmark. Based upon its spectrum, it is categorized as a stony S-type asteroid.[5]

Observations made between 1978 and 1981 produced a composite light curve with two minima and maxima. However, a subsequent study in 1983 only found a single minima and maxima. A synodical rotation period of 7.241 hours was determined. This was confirmed by observations between 1995 and 2000, the changes in brightness and color indicate a surface with an uneven composition.[6]

The asteroid has a slightly elongated shape, with a ratio of 1.20 between the lengths of the major and minor axes. The orbital longitude and latitude of the asteroid pole in degrees is estimated to be (λ0, β0) = (68°, 23°).[7] Measurements of the thermal inertia of 115 Thyra give a value of around 75 m−2 K−1 s−1/2, compared to 50 for lunar regolith and 400 for coarse sand in an atmosphere.[2]


  1. ^ a b c d Yeomans, Donald K., "115 Thyra", JPL Small-Body Database Browser, NASA Jet Propulsion Laboratory, retrieved 12 May 2016. 
  2. ^ a b c d Delbo', Marco; Tanga, Paolo (February 2009), "Thermal inertia of main belt asteroids smaller than 100 km from IRAS data", Planetary and Space Science, 57 (2), pp. 259–265, arXiv:0808.0869Freely accessible, Bibcode:2009P&SS...57..259D, doi:10.1016/j.pss.2008.06.015. 
  3. ^ *JPL Small-Body Database Browser
  4. ^ "Numbered Minor Planets 1–5000", Discovery Circumstances, IAU Minor Planet center, retrieved 2013-04-07. 
  5. ^ DeMeo, Francesca E.; et al. (July 2009), "An extension of the Bus asteroid taxonomy into the near-infrared" (PDF), Icarus, 202 (1), pp. 160–180, Bibcode:2009Icar..202..160D, doi:10.1016/j.icarus.2009.02.005, archived from the original (PDF) on 2014-03-17, retrieved 2013-04-08.  See appendix A.
  6. ^ Michałowski, T.; et al. (March 2004), "Photometry and models of selected main belt asteroids I. 52 Europa, 115 Thyra, and 382 Dodona", Astronomy and Astrophysics, 416, pp. 353–366, Bibcode:2004A&A...416..353M, doi:10.1051/0004-6361:20031706. 
  7. ^ Kryszczyńska, A.; et al. (December 2007), "New findings on asteroid spin-vector distributions", Icarus, 192, pp. 223–237, Bibcode:2007Icar..192..223K, doi:10.1016/j.icarus.2007.06.008. 

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