Polymele imaged by the Hubble Space Telescope in 2018
|Discovery site||Mount Lemmon Obs.|
|Discovery date||17 November 1999|
|MPC designation||(15094) Polymele|
|1999 WB2 · 1997 WR57|
|Jupiter trojan |
|Orbital characteristics |
|Epoch 23 March 2018 (JD 2458200.5)|
|Uncertainty parameter 0|
|Observation arc||24.10 yr (8,803 d)|
|11.74 yr (4,289 d)|
|0° 5m 2.04s / day|
|Jupiter MOID||0.2252 AU|
B–V = 0.652±0.065
V–R = 0.477±0.065
V–I = 0.799±0.068
15094 Polymele (//), provisional designation 1999 WB2, is a primitive Jupiter trojan from the Greek camp, approximately 21 kilometers (13 miles) in diameter. It is a target of the Lucy mission with a close fly by planned to occur in September 2027. It was discovered on 17 November 1999, by astronomers with the Catalina Sky Survey at Mount Lemmon Observatory, Arizona, in the United States. The P-type asteroid has a rotation period of 5.9 hours and possibly a spherical shape. It was named after Polymele from Greek mythology, the wife of Menoetius and the mother of Patroclus.
Orbit and classification
Polymele is a Jupiter trojan (or Jovian asteroid) orbiting in the leading Greek camp at Jupiter's L4 Lagrangian point, 60° ahead of the Gas Giant's orbit (see Trojans in astronomy). It orbits the Sun at a distance of 4.7–5.7 AU once every 11 years and 9 months (4,289 days; semi-major axis of 5.17 AU). Its orbit has an eccentricity of 0.09 and an inclination of 13° with respect to the ecliptic. The asteroid's observation arc begins 48 years prior to its official discovery observation at Mount Lemmon, with a precovery taken at Palomar Observatory in 1951, and published by the Digitized Sky Survey later on.
This minor planet was named after Polymele, the daughter of Peleus from Greek mythology. According to the Latin author Gaius Julius Hyginus (c. 64 BC – AD 17), she is the wife of the Argonaut Menoetius and the mother of Patroclus, who participated in the Trojan War. Polymele is also known as "Philomela"; that name was previously used for the asteroid 196 Philomela. The approved naming citation was published by the Minor Planet Center on 22 February 2016 (M.P.C. 98711).
Lucy mission target
Polymele is planned to be visited by the Lucy spacecraft which will launch in 2021. The fly by is scheduled for 15 September 2027, and will approach the asteroid to a distance of 415 kilometers at a velocity of 6 kilometers per second. The mission's targets with their flyby dates are:
- 52246 Donaldjohanson — 20 April 2025: 4 km diameter C-type asteroid in the inner main-belt, member of ~130Myr old Erigone family;
- 3548 Eurybates — 12 August 2027: 64 km diameter C-type Jupiter Trojan in the Greek camp at L4, largest member of the only confirmed disruptive collisional family in the Trojans;
- 15094 Polymele — 15 September 2027: 21 km diameter P-type Trojan at L4, likely collisional fragment;
- 11351 Leucus — 18 April 2028: 34 km diameter D-type slow rotator Trojan at L4;
- 21900 Orus — 11 November 2028: 51 km diameter D-type Trojan at L4;
- 617 Patroclus — 2 March 2033: P-type binary Trojan. The primary, Patroclus, has a mean diameter of 113 km and its companion, Menoetius, has a diameter of 104 km. The pair orbit at a separation of 680 km. The binary resides in the Trojan camp at L5.
Polymele has been characterized as a primitive P-type asteroid by the investigators of the Lucy mission. P-type asteroids are known for their low albedo. It has a V–I color index of 0.799, which is lower than that for most larger Jupiter trojans (see table below).
Diameter and albedo
According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Polymele measures 21.075 kilometers in diameter and its surface has an albedo of 0.091, while in 2018, Marc Buie published an albedo of 0.073 and an absolute magnitude of 11.691 in the S- and/or R band. The Collaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous asteroid of 0.057 and calculates a larger diameter of 26.64 kilometers based on an absolute magnitude of 11.6.
In March 2016, a rotational lightcurve of Polymele was obtained from photometric observations by Marc Buie and colleges. Lightcurve analysis gave a rotation period of 5.8607±0.0005 hours with a small brightness amplitude of 0.09±0.03 magnitude (U=2-), which indicates that the body has a spheroidal shape. Previously, the Lucy mission team published spin rates of 6.1 and 4 hours, respectively.
- "15094 Polymele (1999 WB2)". Minor Planet Center. Retrieved 8 March 2018.
- "JPL Small-Body Database Browser: 15094 Polymele (1999 WB2)" (2015-06-10 last obs.). Jet Propulsion Laboratory. Retrieved 26 September 2018.
- "List of Jupiter Trojans". Minor Planet Center. 20 June 2016. Retrieved 8 March 2018.
- Grav, T.; Mainzer, A. K.; Bauer, J. M.; Masiero, J. R.; Nugent, C. R. (November 2012). "WISE/NEOWISE Observations of the Jovian Trojan Population: Taxonomy". The Astrophysical Journal. 759 (1): 10. arXiv:1209.1549. Bibcode:2012ApJ...759...49G. doi:10.1088/0004-637X/759/1/49. (online catalog)
- Mainzer, A. K.; Bauer, J. M.; Cutri, R. M.; Grav, T.; Kramer, E. A.; Masiero, J. R.; et al. (June 2016). "NEOWISE Diameters and Albedos V1.0". NASA Planetary Data System: EAR-A-COMPIL-5-NEOWISEDIAM-V1.0. Bibcode:2016PDSS..247.....M. Retrieved 26 September 2018.
- Buie, Marc W.; Zangari, Amanda M.; Marchi, Simone; Levison, Harold F.; Mottola, Stefano (June 2018). "Light Curves of Lucy Targets: Leucus and Polymele" (PDF). The Astronomical Journal. 155 (6): 11. Bibcode:2018AJ....155..245B. doi:10.3847/1538-3881/aabd81. Retrieved 26 September 2018.
- Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90. (catalog)
- Levison, H. F.; Olkin, C.; Noll, K. S.; Marchi, S.; Lucy Team (March 2017). "Lucy: Surveying the Diversity of the Trojan Asteroids: The Fossils of Planet Formation" (PDF). 48th Lunar and Planetary Science Conference (1964): 2025. Bibcode:2017LPI....48.2025L. Retrieved 13 April 2017.
- Hainaut, O. R.; Boehnhardt, H.; Protopapa, S. (October 2012). "Colours of minor bodies in the outer solar system. II. A statistical analysis revisited". Astronomy and Astrophysics. 546: 20. arXiv:1209.1896. Bibcode:2012A&A...546A.115H. doi:10.1051/0004-6361/201219566.
- "LCDB Data for (15094) Polymele". Asteroid Lightcurve Database (LCDB). Retrieved 26 September 2018.
- Buie, Marc W.; Zangari, Amanda Marie; Marchi, Simone; Mottola, Stefano; Levison, Harold F. (October 2016). "Ground-based characterization of Leucus and Polymele, two fly-by targets of the Lucy Discovery mission". American Astronomical Society: 208.06. Bibcode:2016DPS....4820806B.
- "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 8 March 2018.
- Casey Dreier; Emily Lakdawalla (30 September 2015). "NASA announces five Discovery proposals selected for further study". The Planetary Society. Retrieved 12 April 2017.
- Asteroid Lightcurve Database (LCDB), query form (info)
- Dictionary of Minor Planet Names, Google books
- Discovery Circumstances: Numbered Minor Planets (15001)-(20000) – Minor Planet Center
- 15094 Polymele at AstDyS-2, Asteroids—Dynamic Site
- 15094 Polymele at the JPL Small-Body Database