 Polana is in a 1:2 resonance with Mars | |
| Discovery[1] | |
|---|---|
| Discovered by | J. Palisa |
| Discovery site | Austrian Naval Obs. |
| Discovery date | 28 January 1875 |
| Designations | |
| (142) Polana | |
| Pronunciation | [citation needed] |
Named after | Pula |
| A875 BA; 1923 WA; 1954 BH; 1956 XZ; 1963 SA | |
| Asteroid belt | |
| Orbital characteristics[1] | |
| Epoch 31 July 2016 (JD 2457600.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 117.65 yr (42971 d) |
| Aphelion | 2.7444 AU (410.56 Gm) |
| Perihelion | 2.0934 AU (313.17 Gm) |
| 2.4189 AU (361.86 Gm) | |
| Eccentricity | 0.13457 |
| 3.76yr (1374.1d) | |
Averageorbital speed | 19.07 km/s |
| 140.92° | |
| 0° 15m 43.128s / day | |
| Inclination | 2.2379° |
| 291.27° | |
| 292.00° | |
| Physical characteristics | |
| Dimensions | 55.29±1.6 km[1] 55.3 ± 1.6[2] |
| 9.764 h (0.4068 d) | |
| 0.0451±0.003[1] 0.045 ± 0.003[2] | |
| F/B[1] B−V=0.621±0.022[1] U−B=0.236±0.035[1] | |
| 10.27[1] | |
142 Polana is a very darkasteroid from theasteroid belt. It was discovered byJohann Palisa on January 28, 1875, and named after the city of Pola (nowPula, Croatia), home of theAustrian Naval Observatory where he made the discovery.[1]
It is a major member of the eponymously namedPolana family, which is a subgroup of theNysa family.[3] The asteroid has an estimated diameter of about 55.3 km and a lowalbedo of 0.045.[2] It is orbiting at a distance of 2.419 times the separation of the Earth from the Sun, with anorbital period of 3.76 years and aneccentricity of 0.14.
In theTholen classification scheme, Polana is a primitivecarbonaceous asteroid oftype F, which is a subdivision of more commonC-type.[1] Under theSMASS classification taxonomy, Polana is listed as aB-type asteroid, a group that combines both the Tholen B and F types. The spectrum of this object suggests the presence ofmagnetite (Fe3O4), which gives it the spectrally blue coloration that is a characteristic of this SMASS class.[4]
Polana is in a 1:2orbital resonance withMars, 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.[6] In spite of strongperturbations caused by the passing of bothJupiter 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 stronglibration period with Mars.[7]
