1036 Ganymed

For the moon of Jupiter, see Ganymede (moon).

1036 Ganymed, provisional designation 1924 TD, is a stony asteroid on a highly eccentric orbit, classified as a near-Earth object of the Amor group. It was discovered by German astronomer Walter Baade at the Bergedorf Observatory in Hamburg on 23 October 1924, and named after Ganymede from Greek mythology.^[1][2] With a diameter of approximately 35 kilometers (22 miles), Ganymed is the largest of all near-Earth objects but does not cross Earth's orbit. The S-type asteroid has a rotation period of 10.3 hours. In October 2024, it is predicted to approach Earth at a distance of 56,000,000 km; 35,000,000 mi (0.374097 AU).^[15]

1036 Ganymed

Shape model of Ganymed from its lightcurve
Discovery[1]
Discovered by	W. Baade
Discovery site	Bergedorf Obs.
Discovery date	23 October 1924
Designations
MPC designation	(1036) Ganymed
Pronunciation	/ˈɡænəmɛd/
Named after	Ganymede[2] (Greek mythology)
Alternative designations	1924 TD · 1952 BF 1954 HH
Minor planet category	Amor[1][3] · NEO
Adjectives	Ganymedean /ɡænəˈmiːdiən/
Orbital characteristics[3]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc	93.69 yr (34,221 d)
Aphelion	4.0837 AU
Perihelion	1.2421 AU
Semi-major axis	2.6629 AU
Eccentricity	0.5335
Orbital period (sidereal)	4.35 yr (1,587 d)
Mean anomaly	183.36°
Mean motion	0° 13m 36.48s / day
Inclination	26.693°
Longitude of ascending node	215.55°
Argument of perihelion	132.45°
Earth MOID	0.3415 AU (133 LD)
Mars MOID	0.03287 AU[1]
Physical characteristics
Dimensions	39.3 km × 18.9 km[4]
Mean diameter	31.66±2.8 km[5] 35.01±0.78 km[6] 37.675±0.399 km[7][8][9]
Synodic rotation period	10.297 h[10][11]
Geometric albedo	0.218[8][9] 0.243[6] 0.2926[5]
Spectral type	Tholen = S[4] SMASS = S[4][10] S[4][12][13] U–B = 0.417[3] B–V = 0.882±0.008[12] V–R = 0.515±0.004[12] V–I = 0.981±0.005[12]
Absolute magnitude (H)	9.45[1][3][5][6][8][9] 9.50[10][14]

Orbit and classification

Orbit of Ganymed (blue), with the inner planets and Jupiter (outermost).

Ganymed is an Amor asteroid, a subgroup of the near-Earth asteroids that approach the orbit of Earth from beyond, but do not cross it. It orbits the Sun at a distance of 1.2–4.1 AU about once every 4 years and 4 months (i.e., 52 months or 1,587 days; semi-major axis of 2.66 AU). Its orbit has a high eccentricity of 0.53 and an inclination of 27° with respect to the ecliptic.^[3] The body's observation arc begins at the discovering observatory on 24 October 1924 (100 years ago) (1924-10-24), the night after its official discovery observation.^[1]

Close approaches

Earth approach

Ganymed has a minimum orbit intersection distance with Earth of 0.3415 AU (51,000,000 km), or 133 lunar distance. Its next pass of the Earth will be at a distance of 0.374097 AU (56,000,000 km; 34,800,000 mi) on 13 October 2024 (6 months ago) (2024-10-13).^{[15][needs update]}

Mars approach

Due to the high eccentricity of its orbit, Ganymed is also a Mars-crosser, intersecting the orbit of the Red Planet at 1.66 AU. On 16 December 2176 (151 years' time) (2176-12-16), it will pass at a distance of 0.02868 AU (4,290,000 km; 2,670,000 mi) from Mars.^[15]

Name

The minor planet of Ganymed was named after Ganymede from Greek mythology, using the German spelling ("Ganymed"). Ganymede was a Trojan prince abducted by Zeus to serve as a cup-bearer to the Greek gods. The name had previously also been given to Jupiter's third moon, "Ganymede", which was discovered in 1610 by Italian astronomer Galileo Galilei.^[2]

Physical characteristics

Owing to its early discovery date, Ganymed has a rich observational history. A 1931 paper published the absolute magnitude, based on observations to date, as 9.24,^[16] slightly brighter than the present value of 9.45.

Ganymed is a stony S-type asteroid, in the Tholen, SMASS and in the S3OS2 taxonomy. This means that it is relatively reflective and composed of iron and magnesium silicates. Spectral measurements put Ganymed in the S (VI) spectral subtype,^[13] indicating a surface rich in orthopyroxenes, and possibly metals (although if metals are present they are covered and not readily apparent in the spectra).^[13]

Diameter and albedo

According to the 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 (WISE), Ganymed measures between 31.66 and 37.67 kilometers in diameter and its surface has an albedo between 0.218 and 0.293.^{[5][6][7][8][9]}

The Collaborative Asteroid Lightcurve Link derives an albedo of 0.2809 and a mean-diameter of 31.57 kilometers based on an absolute magnitude of 9.50.^[10] Carry published a diameter 34.28±1.38 kilometers in 2012.^[17]

An occultation of a star by Ganymed was observed from California on 22 August 1985.^[4] Additional observations in 2011 gave an occultation cross-section with a semi-major and minor axis of 39.3 and 18.9 kilometers, respectively.^[4]

Rotation and poles

A large number of rotational lightcurves of Ganymed have been obtained from photometric observations since 1985.^{[18][19][20][14][21][22][23][24][25]} Analysis of the best-rated lightcurves obtained by American photometrist Frederick Pilcher at his Organ Mesa Observatory (G50) in New Mexico during 2011 gave a rotation period of 10.297 hours with a consolidated brightness amplitude between 0.28 and 0.31 magnitude (U=3-/3/3).^[10][11]

Three studies using modeled photometric data from the Uppsala Asteroid Photometric Catalogue, WISE thermal infrared data and other sources, gave a concurring period of 10.313, 10.31284, and 10.31304 hours, respectively. Each modeled lightcurve also determined two spin axes of (214.0°, −73.0°), (190.0°, −78.0°), as well as (198.0°, −79.0°) in ecliptic coordinates (λ, β; L1/B1), respectively.^[26][27][28]

In 1998, radar observations of Ganymed by the Arecibo radio telescope produced images of the asteroid, revealing a roughly spherical object.^[29] Polarimetric observations conducted by Japanese astronomers concluded that there was a weak correlation between the object's light- and polarimetry curve as a function of rotation angle.^[30] Because polarization is dependent on surface terrain and composition, rather than the observed size of the object like the lightcurve, this suggests that the surface features of the asteroid are roughly uniform over its observed surface.^[30]