55565 Aya

55565 Aya (provisional designation 2002 AW₁₉₇) is a classical, non-resonant trans-Neptunian object from the Kuiper belt in the outermost region of the Solar System, also known as a cubewano. It was discovered on 10 January 2002 by astronomers at Palomar Observatory.

55565 Aya

Hubble Space Telescope image of Aya taken in December 2005
Discovery[1][2]
Discovered by	Palomar Obs.[a]
Discovery site	Palomar Obs.
Discovery date	10 January 2002
Designations
MPC designation	(55565) Aya
Pronunciation	/ˈaɪə/
Named after	Aya
Alternative designations	2002 AW197
Minor planet category	TNO[3] · classical (hot)[4]: 56  distant[1] · Scat-Ext[5]
Orbital characteristics (barycentric)[6][3]
Epoch 25 February 2023 (JD 2460000.5)
Uncertainty parameter 2[1]
Observation arc	27.15 yr (9,915 d)
Earliest precovery date	29 December 1997
Aphelion	53.280 AU
Perihelion	41.112 AU
Semi-major axis	47.196 AU
Eccentricity	0.1289
Orbital period (sidereal)	324.02 yr (118,349 d)
Mean anomaly	299.003°
Mean motion	0° 0m 10.951s / day
Inclination	24.382°
Longitude of ascending node	297.481°
Time of perihelion	≈ 5 May 2078[7] ±0.4 days[3]
Argument of perihelion	295.928°
Physical characteristics
Mean diameter	768±39 km[8]
Synodic rotation period	8.86±0.01 h[9]: 6 [10]: 1132–1133  8.78 h[11]: 6
Geometric albedo	0.112+0.012 −0.011[8]
Spectral type	IR[12][13] · (moderately red) B–V = 0.920±0.020[14] V–R = 0.560±0.020[14] V–I = 1.170±0.010[13]
Apparent magnitude	20.0[15][1]
Absolute magnitude (H)	3.568±0.046[16] 3.44[3]

Aya is a large object, most likely at least 700 km in diameter. It has a rotation period of 8.8 hours and has a moderately red color.^[12] The object's brightness does not significantly vary as it rotates, which indicates it is likely spheroidal.

History

Discovery

Aya was discovered on 10 January 2002, by astronomers at Palomar Observatory in San Diego County, California, United States.^[1] Astronomers involved in the discovery were Michael Brown, Chad Trujillo, Eleanor Helin, Michael Hicks, Kenneth Lawrence and Steven Pravdo.^[2] The object was discovered during Brown and Trujillo's Caltech Wide Area Sky Survey, which used Palomar Observatory's 1.22-meter (48 in) Samuel Oschin telescope to search for bright Kuiper belt objects.^{[17]: 100, 103} This survey, which was operated jointly with the nightly Near Earth Asteroid Tracking (NEAT) program at Palomar,^[17]: 100 would later discover several other large objects beyond Neptune, including the dwarf planets Eris, Sedna, and Quaoar.^[18]: 214

Aya was found through manual vetting of potential moving objects identified by Brown and Trujillo's automatic image-searching software.^[17]: 101 In terms of absolute magnitude, Aya was the second-brightest Kuiper belt object known at the time.^[19] It was detected at a red-filter apparent magnitude of 19.7.^[2] Aya was further observed by Trujillo and Brown using telescopes at Palomar and Mauna Kea Observatory during February to April 2002.^[2] The discovery was announced by the Minor Planet Center on 20 July 2002 and the object was given the minor planet provisional designation of 2002 AW₁₉₇.^[2]

The 1.2-meter Samuel Oschin telescope that was used to discover Aya at Palomar Observatory

Discovery images of Aya from 10 January 2002

Further observations

Within a month after Aya's discovery, Trujillo and Brown collaborated with Jean-Luc Margot and Frank Bertoldi to measure the object's diameter and thermal emission using the IRAM 30m radio telescope at Sierra Nevada, Spain.^[20][19] Astronomers also found additional observations of Aya from the time before and during its discovery, which allowed for further refinement of orbit calculations.^[21] The earliest pre-discovery observation of Aya comes from an image taken on 29 December 1997 by the NEAT/GEODSS program at Haleakalā Observatory, Hawaii.^[1][21] As of 2025^[update], Aya has been observed for over 27 years, or about 8% of its orbital period.^[3][1]

Numbering and naming

The object received its permanent minor planet catalog number of 55565 from the Minor Planet Center on 16 February 2003.^[22]: 324 On 30 June 2025, it was given the name Aya, after the goddess of dawn and the wife of the sun god Shamash in Akkadian mythology.^[23]: 15

Orbit and classification

Diagram showing top and tilted views of the orbits of Aya (pink), Pluto (purple) and the outer planets

Aya is a trans-Neptunian object (TNO) orbiting the Sun at a semi-major axis or average distance of 47.2 astronomical units (AU).^[6][b] It follows an elliptical orbit with an eccentricity of 0.13.^[6] During its 324-year orbital period, Aya comes within 41.1 AU from the Sun at perihelion and up to 53.3 AU at aphelion.^[6] It has an orbital inclination of 24.4° with respect to the ecliptic.^[6] Aya last passed perihelion in July 1753 and will make its next perihelion passage in May 2078.^[25][7]

Aya is located in the classical region of the Kuiper belt 39–48 AU from the Sun,^[4]: 53 and is thus classified as a classical Kuiper belt object or cubewano.^[4]: 55 Aya's high orbital inclination qualifies it as a dynamically "hot" member of the classical Kuiper belt, which implies that it was gravitationally scattered out to its present location by Neptune's outward planetary migration in the Solar System's early history.^[26]: 230 Hence, Aya is sometimes classified as a "scattered" object.^{[5][27]: 165}

Physical characteristics

History of diameter estimates for Aya

Year of Publication	Diameter (km)	Method	Refs
2002	886+115 −131	thermal (IRAM)	[19][28]: 187
2005	700±50	thermal (Spitzer)	[29][30]
2008	734.6+116.4 −108.3	thermal (Spitzer)	[27]: 172
2009	742+98 −104	thermal (Spitzer, remodeled)	[31]: 291
2014	768±39	thermal (Herschel + Spitzer)	[8]

Size, shape, and rotation

Pair of far-infrared images of Aya by the Spitzer Space Telescope

Measurements of Aya's infrared thermal emission by the Herschel and Spitzer space telescopes give a diameter of 768+39
−38 km (477+24
−24 mi).^[8] This makes Aya slightly smaller than the dwarf planet Ceres.^[19] Aya is large enough that some astronomers consider it a dwarf planet candidate.^{[32][33]: 178} Aya's brightness fluctuates very little as it rotates, which could indicate it has a spheroidal shape.^{[34]: 856–857 [33]: 177}

Aya likely has a rotation period of around 8.8 hours, according to telescopic observations of its brightness changes over time. Aya's subtle brightness variations can make it difficult to determine its light curve and true rotation period.^[11]: 6 The first measurements of Aya's rotation period made during 2002–2003 obtained a likely period of 8.86±0.01 hours.^{[9]: 6 [10]: 1132–1133} Although other alias periods of 13.94, 6.49, and 15.82 hours are possible, the 8.86 hour period stands out as the most likely.^[10]: 1135 Observations from 2003–2004 obtained a period of 8.78 hours,^[11]: 6 whereas another set of observations from 2003 could not determine a period.^{[35]: 790, 795}

Surface

Aya has a dark, reddish surface with a geometric albedo of about 11%.^[8] The visible and near-infrared spectrum of Aya lacks obvious absorption features, which suggests that tholins mostly cover its surface.^[36]

See also

• 174567 Varda – a similar TNO by orbit, size and color
• List of Solar System objects by size

Notes

1. The Minor Planet Center lists "Palomar" as the discoverer without listing specific people.^[1]
2. These orbital elements are expressed in terms of the Solar System Barycenter (SSB) as the frame of reference.^[6] Due to planetary perturbations, the Sun revolves around the SSB at non-negligible distances, so heliocentric-frame orbital elements and distances can vary in short timescales as shown in JPL-Horizons.^[24]