142 Polana
 Polana is in a 1:2 resonance with Mars | |
| Discovery[1] and designation | |
|---|---|
| Discovered by | Johann Palisa |
| Discovery date | January 28, 1875 |
| Designations | |
| Named after | Pula |
| Minor planet category | Main belt |
| Orbital characteristics[1] | |
| 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° |
| Physical characteristics | |
| Dimensions | 55.3 ± 1.6[2] |
| 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] |
| Geometric albedo | 0.045 ± 0.003[2] |
| Temperature | ~179 K |
| Spectral type | F[1] |
| Absolute magnitude (H) | 10.27[1] |
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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]
It is a major member of the eponymously named Polana family, which is a subgroup of the Nysa family.[3] The asteroid has an estimated diameter of about 55.3 km and a low albedo of 0.045.[2] It is orbiting at a distance of 2.419 times the separation of the Earth from the Sun, with an orbital period of 3.76 years and an eccentricity of 0.14.
In the Tholen classification scheme, Polana is a primitive carbonaceous asteroid of type F, which is a subdivision of more common C-type.[1] Under the SMASS classification taxonomy, Polana is listed as a B-type asteroid; a group that combines both the Tholen B and F types. The spectrum of this object suggests the presence of magnetite (Fe3O4), which gives it the spectrally blue coloration that is a characteristic of this SMASS class.[4]
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.[5] 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.[6]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 "142 Polana". JPL Small-Body Database Browser. August 14, 2007, last obs. Retrieved December 17, 2009.
- ↑ 2.0 2.1 2.2 Lazzarin, M.; Barbieri, C.; Barucci, M. A. (December 1995), "Visible Spectroscopy of Dark, Primitive Asteroids", Astronomical Journal 110: 3058, Bibcode:1995AJ....110.3058L, doi:10.1086/117747
- ↑ Cellino, A. et al. (August 2001). "The Puzzling Case of the Nysa-Polana Family". Icarus 152 (2): 225–237. Bibcode:2001Icar..152..225C. doi:10.1006/icar.2001.6634.
- ↑ Yang, Bin; Jewitt, David (September 2010), "Identification of Magnetite in B-type Asteroids", The Astronomical Journal 140 (3): 692–698, arXiv:1006.5110, Bibcode:2010AJ....140..692Y, doi:10.1088/0004-6256/140/3/692
- ↑ Gallardo, Tabaré (2007). "A new population of asteroids: the resonants 1:2 with Mars". Montevideo, Uruguay: Institute of Physics, Faculty of Sciences. Retrieved December 17, 2009.
- ↑ Gallardo, Tabaré (2009). "A New Dynamical Population of Asteroids". RevMexAA (Serie de Conferencias) 35: 21–22.
External links
- Orbital simulation from JPL (Java) / Horizons Ephemeris
- Asteroids inside the resonance 1:2 with Mars (Tabaré Gallardo)
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