1437 Diomedes

Modelled shape of Diomedes from its light curve
Discovery[1]
Discovered by	K. Reinmuth
Discovery site	Heidelberg Obs.
Discovery date	3 August 1937
Designations
MPC designation	(1437) Diomedes
Pronunciation	/ˌdaɪəˈmiːdiːz/[2]
Named after	Diomedes[3] (Greek mythology)
Alternative designations	1937 PB · 1931 DN 1936 PQ · 1971 RD
Minor planet category	Jupiter trojan[1][4][5] Greek[6][7] · background[7]
Adjectives	Diomedian
Orbital characteristics[4]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc	80.80 yr (29,514 d)
Aphelion	5.4248 AU
Perihelion	4.9720 AU
Semi-major axis	5.1984 AU
Eccentricity	0.0435
Orbital period (sidereal)	11.85 yr (4,329 d)
Mean anomaly	234.43°
Mean motion	0° 4m 59.52s / day
Inclination	20.485°
Longitude of ascending node	315.80°
Argument of perihelion	130.93°
Jupiter MOID	0.275 AU
TJupiter	2.8720
Physical characteristics
Dimensions	284 km × 126 km × 65 km[8][9]
Mean diameter	117.79±1.18 km[10] 132.5 km[9] 164.31±4.1 km[11] 172.60±3.42 km[12] 173.0 km[8]
Synodic rotation period	16 h[13] 18 h[14] 21 h[15] 24.46 h[9] 24.49±0.01 h[16][17]
Geometric albedo	0.028±0.001[12] 0.0313±0.002[11] 0.061±0.011[10]
Spectral type	Tholen = DP[4][5][8] U–B = 0.250±040[8] B–V = 0.700±014[8] V–I = 0.810±0.025[5]
Absolute magnitude (H)	8.18±0.28[18] 8.30[1][4][5][10][11][12]

1437 Diomedes /ˌdaɪəˈmiːdiːz/ is a large Jupiter trojan from the Greek camp, approximately 150 kilometers (90 miles) in diameter. It was discovered on 3 August 1937, by astronomer Karl Reinmuth at the Heidelberg-Königstuhl State Observatory in southwest Germany.^[1] The dark D/P-type asteroid belongs to the largest Jupiter trojans and has a notably elongated shape and a longer than average rotation period of 24.49 hours.^[5] Diomedes was the first Jupiter trojan successfully observed during an occultation event of star.^[9] It was named after the hero Diomedes from Greek mythology.^[3]

Orbit and classification

Diomedes is a dark Jovian asteroid orbiting in the leading Greek camp at Jupiter's L₄ Lagrangian point, 60° ahead of the Gas Giant's orbit in a 1:1 resonance (see Trojans in astronomy). It is also a non-family asteroid in the Jovian background population.^[7] Jupiter trojans are thought to have been captured into their orbits during or shortly after the early stages of the formation of the Solar System. More than 4,500 Jupiter trojans in the Greek camp have already been discovered.^[6]

It orbits the Sun at a distance of 5.0–5.4 AU once every 11 years and 10 months (4,329 days; semi-major axis of 5.2 AU). Its orbit has an eccentricity of 0.04 and an inclination of 20° with respect to the ecliptic.^[4] The asteroid was first observed as 1931 DN at Lowell Observatory in February 1931. The body's observation arc begins at Heidelberg with its official discovery observation in August 1937.^[1]

Physical characteristics

In the Tholen classification, Diomedes has an ambiguous spectral type, closest to the dark D-type asteroids and somewhat similar to the primitive P-type asteroids.^[4] Its V–I color index of 0.810 is also lower than that measured for most D-type Jupiter trojans (0.95).^[5]

Rotation period

Several rotational lightcurves of Diomedes have been obtained from photometric observations since the 1960s.^{[9][13][14][15][16]} The so-far best-rated photometric observations by Robert Stephens at the Goat Mountain Astronomical Research Station (G79) and Santana Observatory (646) in November 2008, gave a longer-than average rotation period of 24.49±0.01 hours with a brightness variation of 0.34 magnitude (U=3-).^[17]

Diameter and albedo

In the 1970s, radiometric observations were published in the Tucson Revised Index of Asteroid Data (TRIAD) compilation gave a diameter of 173.0 kilometers with a radiometric albedo 0.021.^[8]

According to the space-based surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Diomedes measures between 117.786 and 172.60 kilometers in diameter and its surface has an albedo between 0.028 and 0.061.^[10][11][12] The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an albedo of 0.0313 and a diameter of 164.31 kilometers based on an absolute magnitude of 8.30.^[5] The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an albedo of 0.0313 and a diameter of 164.31 kilometers based on an absolute magnitude of 8.30.^[5]

Diomedes is the third largest Jupiter trojan according to IRAS and Akari, and the 9th largest based on NEOWISE data:

Occultation and shape

Diomedes was the first Jupiter trojan that was successfully observed during an asteroid occultation, when it occulted the star HIP 014402A over Japan on 7 November 1997. The silhouette was elongated with a major and minor occultation axis of 284 × 126 kilometers (poor fit).^[8][9] The ellipsoid dimensions of 284 × 126 × 65 kilometers – corresponding to a mean-diameter of 132.5 kilometers, equivalent to the volume of a sphere – were estimated using follow-up photometry at Ondřejov Observatory and Mitaka Observatory (388) that determined the body's rotational phase at the exact time of the occultation event.^[9]

Naming

This minor planet was named from Greek mythology after the hero Diomedes, King of Argos and known for his participation in the Trojan War, regarded as the best warriors of the Achaeans, just behind Achilles and alongside Ajax. The official naming citation was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 129).^[3]