55565 Aya

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.^{[16]: 100, 103 } This survey, which was operated jointly with the nightly Near Earth Asteroid Tracking (NEAT) program at Palomar,^{[16]: 100 } would later discover several other large objects beyond Neptune, including the dwarf planets Eris, Sedna, and Quaoar.^{[17]: 214 }

Aya was found through manual vetting of potential moving objects identified by Brown and Trujillo's automatic image-searching software.^{[16]: 101 } In terms of absolute magnitude, Aya was the second-brightest Kuiper belt object known at the time.^[18] 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.^[19][18] Astronomers also found additional observations of Aya from the time before and during its discovery, which allowed for further refinement of orbit calculations.^[20] 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][20] 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.^{[21]: 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.^{[22]: 15 }

Size, shape, and rotation

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.^[18] Aya is large enough that some astronomers consider it a dwarf planet candidate.^{[31][32]: 178 } Aya's brightness fluctuates very little as it rotates, which could indicate it has a spheroidal shape.^{[33]: 856–857 [32]: 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.^{[34]: 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.^[35]