308 Polyxo

308 Polyxo is a main-belt asteroid that was discovered by Alphonse Borrelly on 31 March 1891, in Marseille. It is orbiting the Sun at a distance of 2.75 AU with a low orbital eccentricity (ovalness) of 0.04 and a period of 4.56 yr. The orbital plane is tilted at an angle of 4.36° to the plane of the ecliptic.^[2]

308 Polyxo

Orbital diagram
Discovery
Discovered by	Alphonse Borrelly
Discovery date	31 March 1891
Designations
MPC designation	(308) Polyxo
Pronunciation	/pəˈlɪksoʊ/[1]
Named after	Πολυξώ Polyxō
Minor planet category	Main belt
Adjectives	Polyxoian /pɒlɪkˈsoʊiən/
Orbital characteristics[2]
Epoch 31 July 2016 (JD 2457600.5)
Uncertainty parameter 0
Observation arc	124.63 yr (45,521 d)
Aphelion	2.860 AU (427.8 Gm)
Perihelion	2.640 AU (394.9 Gm)
Semi-major axis	2.750 AU (411.4 Gm)
Eccentricity	0.040003
Orbital period (sidereal)	4.56 yr (1,665.5 d)
Mean anomaly	70.4189°
Mean motion	0° 12m 58.158s / day
Inclination	4.36141°
Longitude of ascending node	181.727°
Argument of perihelion	115.501°
Physical characteristics
Dimensions	140.69±3.8 km[2] 130 km[3]
Synodic rotation period	12.031 ± 0.009 h (0.50129 ± 0.00038 d)[4]
Geometric albedo	0.043±0.002[5]
Spectral type	T[4] (Tholen)
Absolute magnitude (H)	8.17

308 Polyxo is classified as a rare T-type asteroid, with a spectrum that bears some similarity to the Tagish Lake meteorite.^[6] A spectral feature at a wavelength of 3.0 μm suggests aqueous alteration of some surface materials.^[4] Photometric measurements reported in 1983 give a rotation period of 12.03 hours and a brightness variation of 0.20 in magnitude. The adaptive optics instrument at the W. M. Keck Observatory shows an oblate object with a diameter of 130 km. The size ratio between the major and minor axes is 1.26 ± 0.11.^[3] Light curves for this object suggests it has a very irregular shape.^[4]

Stellar occultation events were observed for this asteroid during 2000 and 2004. The resulting chords provided cross-section diameter estimates of 144.4 and 117.1 km, respectively.^[7]