 Orbit of 33 Polyhymnia (1 Jan 2009) | |
| Discovery[1] | |
|---|---|
| Discovered by | J. Chacornac |
| Discovery date | October 28, 1854 |
| Designations | |
| (33) Polyhymnia | |
| Pronunciation | /pɒliˈhɪmniə/[2] |
Named after | Polyhymnia |
| A887 HA; 1938 FE; 1953 AK; 1957 YL; 1963 DG;1976 YT7 | |
| Main belt | |
| Orbital characteristics[3] | |
| Epoch April 18, 2013 (JD 2456400.5) | |
| Aphelion | 573.518 Gm (3.83373 AU) |
| Perihelion | 284.409 Gm (1.90116 AU) |
| 428.964 Gm (2.86745 AU) | |
| Eccentricity | 0.33698 |
| 1,773.541 d (4.86 a) | |
| 256.476° | |
| Inclination | 1.869° |
| 8.595° | |
| 338.123° | |
| Physical characteristics | |
| Dimensions | 54.39±11.84 km (infrared)[4] 53.98±0.91 km[5] 64±6 km (occultation)[6] |
| 18.60888±0.00029 h[7] | |
| S[3] orSq[8] | |
| 8.55[3] | |
33 Polyhymnia is amain beltasteroid that was discovered by French astronomerJean Chacornac on October 28, 1854[1] and named afterPolyhymnia, theGreekMuse of sacredhymns.
Photometric observations of this asteroid at the Organ Mesa Observatory inLas Cruces, New Mexico during 2008 gave alight curve with a period of 18.609 ± 0.002 hours and a brightness variation of 0.15 ± 0.02 inmagnitude. This result is in good agreement with a previous study performed during 1980.[9] These results were re-examined with additional observations in 2011, yielding a refined estimate of 18.608 ± 0.001 hours and a brightness variation of 0.18 ± 0.02 magnitude.[10] In 2020, an analysis of photometric data of Polyhymnia from 2008 to 2019 determined a more precise rotation period of18.60888±0.00029 h. Two possible north pole orientations of Polyhymnia were also determined, with both solutions indicating anaxial tilt of 151–155° (ecliptic latitudes –61° to –65°) with respect to theecliptic.[7]
On its highlyeccentric (0.338) orbit around the Sun, 33 Polyhymnia appears brightest (apparent magnitude 10) at itsminimum distance from Earth of 0.91 AU.[11] Its orbit puts it in a 22:9mean-motion resonance with the planetJupiter. The computedLyapunov time for this asteroid is 10,000 years, indicating that it occupies a chaotic orbit that will change randomly over time because ofgravitational perturbations of the planets.[12] Measurements of the position for this asteroid from 1854 to 1969 were used to determine the gravitational influence of Jupiter upon 33 Polyhymnia. This yields an inverse mass ratio of1047.341±0.011 for Jupiter relative to the Sun.[13]
In 2012, a study by Benoît Carry gave a meta-estimate of a mass of(6.20±0.74)×1018 kg for Polyhymnia, based on a single study of its gravitational influence on other Solar System bodies.[5] However, given Polyhymnia's diameter of 54 km (34 mi), this mass implies an extremely highdensity of75.28±9.71 g/cm3. Such a high density is unrealistic, so this mass and density estimate of Polyhymnia was considered unreliable by Carry.[5] Several other asteroids with diameters similar to Polyhymnia were also measured to have extremely high densities in Carry's study, and were rejected for being unrealistic.[5] Because of Polyhymnia's small size, its gravitational influence on other bodies is extremely difficult to detect and may lead to highly inaccurate mass and density estimates.[5] For example, the 68 km (42 mi)-diameter asteroid675 Ludmilla was originally measured to have a density of73.99±15.05 g/cm3 in Carry's study,[5] but improved orbit calculations in 2019 showed that it had a much lower density of3.99±1.94 g/cm3.[14]
No otherpeer-reviewed study has attempted to determine a mass and density for Polyhymnia since Carry's study,[15] though in 2023, researcher Fan Li performed a preliminary analysis of Polyhymnia's close approaches with other asteroids and determined a lower mass of(1.03±0.40)×1018 kg.[16] Depending on the diameter used for Polyhymnia, this mass estimate suggests a density of7.5±3.6 g/cm3 or12.4 g/cm3, for anoccultation-derived diameter of 64 ± 6 km (39.8 ± 3.7 mi) and infrared-derived diameter of 54 km (34 mi), respectively.[16][17]
Visible lightspectroscopy of Polyhymnia from 1995 and 2002 show that it is anS-type asteroid, meaning it is mainly composed of rockysilicates.[3] In particular, Polyhymnia's spectrum exhibits anabsorption band at 0.67 μm wavelengths, which indicatesolivine andpyroxene on its surface, similar toQ-type asteroids.[8]: 155, 164–165 Since Polyhymnia shares both characteristics of S- and Q-type asteroids, it is further classified as an Sq-type asteroid according to theSMASS classification.[8]: 155, 164–165 Radio telescopes have studied Polyhymnia byradar in 1985.[18][19]
In 2023, researchers Evan LaForge, Will Price, and Johann Rafelski speculated the possibility that Polyhymnia could be composed of high-densitysuperheavy elements near atomic number 164, if Polyhymnia's extremely high density were correct and superheavy elements could besufficiently stable.[20] However, as noted above, Polyhymnia very likely does not have such a high density.[16][17]
