140 Siwa

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140 Siwa
Discovered byJ. Palisa
Discovery siteAustrian Naval Obs.
Discovery date13 October 1874
MPC designation(140) Siwa
Main belt
Orbital characteristics[1]
Epoch 31 July 2016 (JD 2457600.5)
Uncertainty parameter 0
Observation arc139.10 yr (50805 d)
Aphelion3.3224 AU (497.02 Gm)
Perihelion2.14323 AU (320.623 Gm)
2.73283 AU (408.826 Gm)
4.52 yr (1650.1 d)
17.80 km/s
0° 13m 5.398s / day
Physical characteristics
Dimensions109.79±3.0 km
Mass1.4×1018 kg
34.445 h (1.4352 d)[1]
34.407 h[2]
C-type asteroid[3]

Siwa (/ˈʃwə/; minor planet designation: 140 Siwa) is a large and dark main-belt asteroid that was discovered by Austrian astronomer Johann Palisa on October 13, 1874, and named after Šiwa, the Slavic goddess of fertility.

The Rosetta comet probe was to visit Siwa on its way to comet 46P/Wirtanen in July, 2008. However, the mission was rerouted to comet 67P/Churyumov-Gerasimenko and the flyby had to be abandoned.[4]

Attempts to measure the rotation period of this asteroid have produced inconsistent results ranging from 14.7 to 32 hours. Photometric observations of this asteroid at the Organ Mesa Observatory in Las Cruces, New Mexico during 2010 gave an irregular light curve with a period of 34.407 ± 0.002 hours and a brightness variation of 0.05 ± 0.01 in magnitude.[2]

A 2004 study of the spectrum matched a typical C-type asteroid with typical carbonaceous chondrite makeup. There are no absorption features of mafic minerals found.[3] The classification was later revised to a P-type asteroid.[5]


  1. ^ a b Yeomans, Donald K., "140 Siwa", JPL Small-Body Database Browser, NASA Jet Propulsion Laboratory, retrieved 12 May 2016.
  2. ^ a b Pilcher, Frederick (April 2011), "Rotation Period Determinations for 25 Phocaea, 140 Siwa, 149 Medusa 186 Celuta, 475 Ocllo, 574 Reginhild, and 603 Timandra", The Minor Planet Bulletin, 38 (2), pp. 76–78, Bibcode:2011MPBu...38...76P.
  3. ^ a b Birlan, Mirel; et al. (April 2004), "Near-IR spectroscopy of asteroids 21 Lutetia, 89 Julia, 140 Siwa, 2181 Fogelin and 5480 (1989YK8), potential targets for the Rosetta mission; remote observations campaign on IRTF", New Astronomy, 9 (5), pp. 343–351, arXiv:astro-ph/0312638, Bibcode:2004NewA....9..343B, doi:10.1016/j.newast.2003.12.005.
  4. ^ Greyzeck, Ed (2013), "Rosetta", NSS Data Center, NASA, retrieved 2013-03-30.
  5. ^ Takir, Driss; Emery, Joshua P. (June 2012), "Outer Main Belt asteroids: Identification and distribution of four 3-μm spectral groups", Icarus, 219 (2), pp. 641–654, Bibcode:2012Icar..219..641T, doi:10.1016/j.icarus.2012.02.022.

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