5 Astraea

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5 Astraea 5 Astraea Symbol.svg
5Astraea (Lightcurve Inversion).png
A three-dimensional model of Astraea based on its light curve.
Discovery
Discovered by Karl Ludwig Hencke
Discovery date December 8, 1845
Designations
Pronunciation /æˈstrə/ a-STREE
Named after Astraea
Alternative names 1969 SE
Minor planet category Main belt
Adjective Astraean
Orbital characteristics
Epoch November 26, 2005 (JD 2453700.5)
Aphelion 459.202 Gm (3.070 AU)
Perihelion 310.688 Gm (2.077 AU)
Semi-major axis 384.945 Gm (2.573 AU)
Eccentricity 0.193
Orbital period 1507.676 d (4.13 a)
Average orbital speed 18.39 km/s
Mean anomaly 194.442°
Inclination 5.369°
Longitude of ascending node 141.690°
Argument of perihelion 357.530°
Proper orbital elements[1]
Proper semi-major axis 2.5761849 AU
Proper eccentricity 0.1980486
Proper inclination 4.5118628°
Proper mean motion 87.046396 deg / yr
Proper orbital period 4.13573 yr
(1510.574 d)
Precession of perihelion 52.210903 arcsec / yr
Precession of the ascending node −57.357951 arcsec / yr
Physical characteristics
Dimensions 167×123×82 km[2][3]
119 km (mean)
Mass 2.9×1018 kg[4][5]
(assumed)[6]
Mean density ~3.3 g/cm³
Equatorial surface gravity ~0.023 m/s²
Escape velocity ~0.062 km/s
Rotation period 0.700 03 d (16.801 h)[3]
Albedo 0.227 (geometric)[2]
Temperature ~167 K
max: 263 K (-10 °C)
Spectral type S-type asteroid
Apparent magnitude 8.74 to 12.89
Absolute magnitude (H) 6.85
Angular diameter 0.15" to 0.041"

5 Astraea is a large asteroid from the asteroid belt. Its surface is highly reflective (bright) and its composition is probably a mixture of nickeliron with silicates of magnesium and iron. It is an S-type object in the Tholen classification system.[7]

Size comparison: the first 10 asteroids profiled against Earth's Moon. Astraea is the fifth from the left.

Astraea was the fifth asteroid discovered, on December 8, 1845, by K. L. Hencke and named for Astræa, a goddess of justice named after the stars. It was his first of two asteroid discoveries. The second was 6 Hebe. An amateur astronomer and post office employee, Hencke was looking for 4 Vesta when he stumbled on Astraea. The King of Prussia awarded him an annual pension of 1,200 marks for the discovery.[8]

Photometry indicates prograde rotation, that the north pole points in the direction of right ascension 9 h 52 min, declination 73° with a 5° uncertainty.[3] This gives an axial tilt of about 33°.

The orbit of 5 Astraea compared with the orbits of Earth, Mars and Jupiter

Astraea is physically unremarkable but notable mainly because for 38 years (after the discovery of Vesta in 1807) it had been thought that there were only four asteroids.[9] In terms of maximum brightness, it is indeed only the seventeenth brightest main-belt asteroid, being fainter than 192 Nausikaa and even, at rare near-perihelion oppositions, the highly eccentric carbonaceous 324 Bamberga.[1] It will be at magnitude +8.7 on a favorable opposition on February 15, 2016.

After the discovery of Astraea, thousands of other asteroids would follow. Indeed, the discovery of Astraea proved to be the starting point for the eventual demotion of the four original asteroids (which were regarded as planets at the time)[9] to their current status, as it became apparent that these four were only the largest of a whole new type of celestial body.

An occultation on 6 June 2008 produced an effective diameter (silhouette) of 115±6 km.[10]

Astraea has been studied by radar.[11] Arecibo observed Astraea in March 2012.[12][13]

References[edit]

  1. ^ "AstDyS-2 Astraea Synthetic Proper Orbital Elements". Department of Mathematics, University of Pisa, Italy. Retrieved 2011-10-01. 
  2. ^ a b Supplemental IRAS Minor Planet Survey
  3. ^ a b c M. J. López-Gonzáles & E. Rodríguez Lightcurves and poles of seven asteroids, Planetary and Space Science, Vol. 53, p. 1147 (2005).
  4. ^ Michalak, G. (2001). "Determination of asteroid masses". Astronomy & Astrophysics 374 (2): 703–711. Bibcode:2001A&A...374..703M. doi:10.1051/0004-6361:20010731. Retrieved 2008-11-10. 
  5. ^ (Mass estimate of Astra 0.015 / Mass of Ceres 4.75) * Mass of Ceres 9.43E+20 = 2.977E+18
  6. ^ Michalak2001 (Table 6) assumed masses of perturbing asteroids used in calculations of perturbations of the test asteroids.
  7. ^ "JPL Small-Body Database Browser: 5 Astraea
  8. ^ "Dawn Community". NASA. Archived from the original on 21 May 2009. Retrieved 2009-04-17. 
  9. ^ a b "The Planet Hygea". spaceweather.com. 1849. Archived from the original on 9 April 2008. Retrieved 2008-04-18. 
  10. ^ Ďurech, Josef; Kaasalainen, Mikko; Herald, David; Dunham, David; Timerson, Brad; Hanuš, Josef; Frappa, Eric; Talbot, John; Hayamizu, Tsutomu; Warner, Brian D.; Pilcher, Frederick; Galád, Adrián (2011). "Combining asteroid models derived by lightcurve inversion with asteroidal occultation silhouettes". Icarus 214 (2): 652–670. arXiv:1104.4227. Bibcode:2011Icar..214..652D. doi:10.1016/j.icarus.2011.03.016. 
  11. ^ "Radar-Detected Asteroids and Comets". NASA/JPL Asteroid Radar Research. Retrieved 2012-01-23. 
  12. ^ Mike Nolan (2012-01-18). "Scheduled Arecibo Radar Asteroid Observations". Planetary Radar at Arecibo Observatory. Retrieved 2012-01-23. 
  13. ^ http://www.naic.edu/~pradar/

External links[edit]