142 Polana
Polana is in a 1:2 resonance with Mars
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Discovery[1] and designation
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| Discovered by | Johann Palisa |
| Discovery date | January 28, 1875 |
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Designations
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| Named after | Pula |
| Minor planet category |
Main belt |
| Epoch January 4, 2010 (JD 2455200.5) | |
| Aphelion | 410.945 Gm (2.747 AU) |
| Perihelion | 312.210 Gm (2.087 AU) |
| Semi-major axis | 361.578 Gm (2.417 AU) |
| Eccentricity | 0.1365 |
| Orbital period | 1372.9 d (3.76 a) |
| Average orbital speed | 19.07 km/s |
| Mean anomaly | 232.13° |
| Inclination | 2.237° |
| Longitude of ascending node | 291.33° |
| Argument of perihelion | 291.82° |
| Dimensions | 55.3 km[1] |
| Mass | 1.8×1017 kg |
| Mean density | 2.0 g/cm³ |
| Equatorial surface gravity | 0.0155 m/s² |
| Equatorial escape velocity | 0.0292 km/s |
| Sidereal rotation period |
9.764 hr[1] |
| Axial tilt | ?° |
| Pole ecliptic latitude | ? |
| Pole ecliptic longitude | ? |
| Geometric albedo | 0.045[1] |
| Temperature | ~179 K |
| Spectral type | F[1] |
| Absolute magnitude (H) | 10.27[1] |
142 Polana is a very dark main belt asteroid. It was discovered by Johann Palisa on January 28, 1875, and named after the city of Pola (now Pula, Croatia), home of the Austrian Naval Observatory where he made the discovery.[1]
Polana is a primitive carbonaceous asteroid of type F (a subdivision of more common C-type).[1] It is a major member of the Polana family, which is a subgroup of the Nysa family.[2]
[edit] Mars resonance
Polana is in a 1:2 orbital resonance with Mars, meaning that Polana orbits the Sun once for every two orbits that Mars completes. This resonance helps protect the asteroid from orbital erosion: the orbital eccentricities of the resonant asteroids are clearly greater than the non-resonant asteroids. There is a peak in the number of asteroids located at 2.419 AU from the Sun.[3] In spite of strong perturbations caused by the passing of both Jupiter and Mars, the 1:2 Mars resonance brings about stability for billions of years. There are up to 1,500 asteroids in this resonance, and the resonance between Polana and Mars will strengthen over the next million years due to Polana transitioning into a strong libration period with Mars.[4]
[edit] References
- ^ a b c d e f g h i "JPL Small-Body Database Browser: 142 Polana". August 14, 2007 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Polana. Retrieved December 17, 2009.
- ^ A. Cellino, V. Zappala, A. Doressoundiram, M. Di Martino, P. Bendjoya, E. Dotto & F. Migliorini (August 2001). "The Puzzling Case of the Nysa-Polana Family". Icarus (Icarus) 152 (2): 225–237. Bibcode 2001Icar..152..225C. doi:10.1006/icar.2001.6634. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-458NDHM-M&_user=994540&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050024&_version=1&_urlVersion=0&_userid=994540&md5=f06ca90a1bfa6af70955b5a31f31e82f.
- ^ Dr. Tabare Gallardo (2007). "A new population of asteroids: the resonants 1:2 with Mars". Institute of Physics, Faculty of Sciences, Montevideo, Uruguay. http://www.fisica.edu.uy/~gallardo/marte12/mars1to2.html. Retrieved December 17, 2009.
- ^ Tabare Gallardo. "A New Dynamical Population of Asteroids". RevMexAA (Serie de Conferencias), 35, 21-22 (2009). http://www.astroscu.unam.mx/rmaa/RMxAC..35/PDF/RMxAC..35_tgallardo.pdf. Retrieved December 17, 2009.
[edit] External links
- Orbital simulation from JPL (Java) / Horizons Ephemeris
- Asteroids inside the resonance 1:2 with Mars (Tabare Gallardo)
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