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944 Hidalgo

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944 Hidalgo

944 Hidalgo
Discovery
Discovered by Walter Baade
Discovery date October 31, 1920
Designations
Named after
Miguel Hidalgo y Costilla
1920 HZ
Jupiter-crosser asteroid,
Saturn-crosser asteroid
centaur[1]
Orbital characteristics
Epoch July 14, 2004 (JD 2453200.5)
Aphelion 9.539 AU
(1427.003 Gm)
Perihelion 1.951 AU
(291.846 Gm)
5.745 AU
(859.425 Gm)
Eccentricity 0.660
13.77 yr
(5029.467 d)
Average orbital speed
12.43 km/s
346.285°
Inclination 42.567°
21.549°
56.569°
Physical characteristics
Dimensions 38 km[1]H
0.419 29 d[2]
Albedo 0.06 (assumed)[1]
Temperature ~116 K
Spectral type
D-type asteroid
10.77[1]

944 Hidalgo ( ) is a small Solar System body with a semi-major axis beyond Jupiter's and an orbital period of 13.77 years. This makes it a centaur, the first to be discovered, but it was discovered in 1920 and has hence traditionally been called an asteroid. Hidalgo is estimated to be 38 km in diameter.[1]

Discovery and subsequent studies

944 Hidalgo trajectory

944 Hidalgo was discovered by Walter Baade on October 31, 1920 at Bergedorf Observatory near Hamburg, Germany. It is named for Miguel Hidalgo y Costilla, who was responsible for declaring Mexico's independence in 1810 and the ensuing Mexican War of Independence. German astronomers who were in Mexico to observe a total eclipse on September 10, 1923, had an audience with President Álvaro Obregón. During this meeting, they asked his permission to name the asteroid after Hidalgo.[3]

It was one of five minor planets included in the 1993 study, Transition Comets—UV Search for OH Emissions in Asteroids, which was research involving amateur astronomers who were permitted to make use of the Hubble Space Telescope.

In the late 1990s, a network of astronomers worldwide gathered light curve data that was ultimately used to derive the spin states and shape models of 10 new asteroids, including 944 Hidalgo. The authors describe the shape model as having 'very large flat areas and a "rectangular" pole-on silhouette, which are strong indications of a highly nonconvex shape'. Some of the light curves show sharp minima, which indicates the object shape may have two lobes.[4][5] Lightcurve data has also been recorded by observers at the Antelope Hills Observatory, which has been designated as an official observatory by the Minor Planet Center.[6]

When Pluto was discovered Hidalgo was the furthest known minor planet from the Sun.[7]

Orbit

944 Hidalgo is a centaur[1] because it has a semi-major axis between Jupiter's and Neptune's. Despite this, the Minor Planet Center (MPC) does not list it as a centaur.[8] Hidalgo has traditionally been considered an asteroid because centaurs were not recognized as a distinct class until the discovery of 2060 Chiron in 1977.

With a high eccentricity of 0.66, its perihelion of 1.95 AU takes it to the inner edge of the asteroid belt, whereas its aphelion of 9.54 AU takes it out to Saturn's orbit, a characteristic normally associated with Saturn's family of comets. Some astronomers therefore suspect that it was once a comet. Strictly speaking, Hidalgo is a Saturn-grazer rather than a Saturn-crosser as its aphelion does not clear Saturn's. Hidalgo's severe orbital inclination of 43° is suspected to be the result of a close encounter with Jupiter. Even as recently as 1922, Hidalgo passed within 0.89 AU of Jupiter,[9] significantly affecting its orbit.

References

  1. ^ a b c d e f "JPL Small-Body Database Browser: 944 Hidalgo (1920 HZ)" (2008-05-09 last obs). Retrieved 2008-03-09. 
  2. ^ "Minor planet lightcurve parameters". Ipa.nw.ru. Retrieved 2013-10-30. 
  3. ^ Schmadel Lutz D. Dictionary of Minor Planet Names (fifth edition), Springer, 2003. ISBN 3-540-00238-3.
  4. ^ Durech, J.; et al. (April 2007), "Physical models of ten asteroids from an observers' collaboration network", Astronomy and Astrophysics 465 (1): 331–337,  
  5. ^ Durech, J.; Kaasalainen, M.; Marciniak, A.; Allen, W. H. et al. “Asteroid brightness and geometry,” Astronomy and Astrophysics, Volume 465, Issue 1, April I 2007, pp. 331-337.
  6. ^ http://www.antelopehillsobservatory.org/Lightcurves/944.gif
  7. ^ "JPL Small-Body Database Search Engine". JPL Solar System Dynamics. Archived from the original on 31 May 2008. Retrieved 2008-05-27.  (characteristic:a>5.7)
  8. ^ "List Of Centaurs and Scattered-Disk Objects". Minor Planet Center. Retrieved 2008-10-04. 
  9. ^ "JPL Close-Approach Data: 944 Hidalgo (1920 HZ)" (2008-06-10 last obs). Retrieved 2009-05-05. 

External links

  • Orbital simulation from JPL (Java) / Horizons Ephemeris
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