142 Polana is a very dark

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

from the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...

. It was discovered by

Johann Palisa Johann Palisa (6 December 1848 – 2 May 1925) was an Austrian astronomer, born in Troppau, Austrian Silesia, now Czech Republic. He was a prolific discoverer of asteroids, discovering 122 in all, from 136 Austria in 1874 to 1073 G ...

on January 28, 1875, and named after the city of Pola (now

Pula, Croatia Pula, also known as Pola, is the largest city in Istria County, west Croatia, and the List of cities and towns in Croatia, seventh-largest city in the country, situated at the southern tip of the Istria, Istrian peninsula in western Croatia, wi ...

), home of the Austrian Naval Observatory where he made the discovery. It is a major member of the eponymously named

Polana family Polana may refer to the following places: Places *Polana, Lower Silesian Voivodeship (south-west Poland) *Polana, Subcarpathian Voivodeship (south-east Poland) *Polana, Opole Voivodeship (south-west Poland) *Polana, Pomeranian Voivodeship (north P ...

, which is a subgroup of the

Nysa family The Nysa family (adj. ''Nysian''; FIN: 405) is part of the Nysa–Polana complex, the largest cluster of asteroid families in the asteroid belt. It is located in the inner region of the asteroid belt, orbiting the Sun between 2.41 and 2.5 ...

. The asteroid has an estimated diameter of about 55.3 km and a low

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

of 0.045. It is orbiting at a distance of 2.419 times the separation of the Earth from the Sun, with an

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

of 3.76 years and an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.14. In the

Tholen classification An asteroid spectral type is assigned to asteroids based on their reflectance spectrum, color, and sometimes albedo. These types are thought to correspond to an asteroid's surface composition. For small bodies that are not internally different ...

scheme, Polana is a primitive

carbonaceous Carbonaceous refers to something relating to, containing, or composed of carbon. It is a descriptor used for the attribute of any substance rich in carbon. Particularly, ''carbonaceous hydrocarbons'' are very unsaturated, high- molecular-weight h ...

asteroid of type F, which is a subdivision of more common C-type. Under the

SMASS classification An asteroid spectral type is assigned to asteroids based on their reflectance spectrum, color, and sometimes albedo. These types are thought to correspond to an asteroid's surface composition. For small bodies that are not internally different ...

taxonomy, Polana is listed as a

B-type asteroid B-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-type asteroid#C-group asteroids, C-group; the 'B' indicates these objects are spectrally blue. In the asteroid population, B-class objects can be f ...

, a group that combines both the Tholen B and F types. The spectrum of this object suggests the presence of

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...

(Fe₃O₄), which gives it the spectrally blue coloration that is a characteristic of this SMASS class.

Mars resonance

Polana is in a 1:2

orbital resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relation ...

with

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

, 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. In spite of strong perturbations caused by the passing of both

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

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 In lunar astronomy, libration is the cyclic variation in the apparent position of the Moon that is perceived by observers on the Earth and caused by changes between the orbital and rotational planes of the moon. It causes an observer to see ...

period with Mars.

References

External links

Asteroids inside the resonance 1:2 with Mars
Tabaré Gallardo * * {{DEFAULTSORT:Polana 000142 Discoveries by Johann Palisa Named minor planets Mars 000142 000142 18750128