(612533) 2002 XV93

(612533) 2002 XV₉₃

2002 XV93 imaged by the Hubble Space Telescope in August 2005
Discovery1
Discovered by	Palomar
Discovery site	Palomar Observatory
Discovery date	10 December 2002
Designations
Minor planet category	TNO2 · plutino34 · distant1
Orbital characteristics (barycentric)5a
Epoch 21 November 2025 (JD 2461000.5)
Uncertainty parameter 22
Observation arc	35+ yr2
Earliest precovery date	16 October 1990
Aphelion	44.212 AU
Perihelion	34.405 AU
Semi-major axis	39.309 AU
Eccentricity	0.1247
Orbital period (sidereal)	246.29 yr (89,958 d)
Mean anomaly	295.225°
Mean motion	0° 0m 12.241s / day
Inclination	13.270°
Longitude of ascending node	19.043°
Time of perihelion	20 March 2070 ±1.10 days62
Argument of perihelion	164.647°
Known satellites	0
Physical characteristics
Mean diameter	470+44 −30 km (2026)4 549.2+21.7 −23.0 km (2012)7
Geometric albedo	>0.040+0.020 −0.015 (2012)7c
Surface temp. min mean max Kelvin4 40 47 50
Spectral type	Prominent water (H 2O/"bowl" type)9: 4  B−V = 0.72±0.0278 V−R = 0.37±0.0278
Apparent magnitude	20.810
Absolute magnitude (H)	4.73 (2016)28: 5  5.42±0.46 (2012)7: 4
Atmosphere
Surface pressure	100–200 nbar (0.01–0.02 Pa)4
Composition by volume	unknown; nitrogen, argon, or methane?11

(612533) 2002 XV₉₃ is an unnamed trans-Neptunian object (TNO) in the Kuiper belt, discovered by Palomar Observatory in December 2002. It is a member of the plutinos, a population of TNOs in a 2:3 orbital resonance with Neptune, like the dwarf planet Pluto. 2002 XV₉₃ has a diameter of around 430 to 510 km (270 to 320 mi), which makes it about one-seventh the diameter of Earth's moon and about one-fifth the diameter of Pluto. It has a dark gray surface containing high amounts of water ice and some frozen carbon dioxide, but no detectable signs of frozen methane, nitrogen, or carbon monoxide. The mass, density, shape, and rotation of 2002 XV₉₃ are all unknown, but are expected to resemble those of other similarly-sized TNOs like Huya.

In 2026, astronomers announced the discovery of a thin atmosphere around 2002 XV₉₃, making it likely the first TNO after Pluto discovered to have an atmosphere,^d and defying expectations that it should be too small to hold onto an atmosphere. With a surface pressure of 100–200 nanobars (roughly 5 million to 10 million times thinner than Earth's atmosphere or 50 to 100 times thinner than Pluto's atmosphere), it is predicted that 2002 XV₉₃ should lose all of its atmosphere in 100 to 1,000 years. The existence of 2002 XV₉₃'s atmosphere suggests it was recently replenished, either by a comet impact or outgassing via cryovolcanic eruptions. The composition of the atmosphere is unknown, but it is thought to contain either nitrogen, argon, or methane.¹¹

2002 XV₉₃ was discovered on 10 December 2002 (Universal Time; UT) by Palomar Observatory^e in California, United States.¹ At that time, a team of astronomers led by Chad Trujillo and Michael E. Brown were working in Palomar Observatory using its 1.2-m Samuel Oschin telescope, operating jointly with the Near-Earth Asteroid Tracking (NEAT) program.^{1213: 100, 103} The object's discovery was announced by the Minor Planet Center (MPC) on 5 January 2003.¹² Precovery observations of 2002 XV₉₃ from Palomar Observatory were later identified in 2008, with the observations dating to 16 October 1990, 12 October 1991, and 28 September 1992.¹⁴

On 10 January 2024 (UT), 2002 XV₉₃ passed in front of a magnitude-15.8 star in the constellation Auriga, causing it to briefly dim from Earth for up to 20 seconds.^{1516: 4 f} This event, known as a stellar occultation, was predicted and observed in Japan by a team of astronomers led by Ko Arimatsu of the National Astronomical Observatory of Japan.^{15174: 1, 8} Telescopes were stationed at Kyoto University, Kiso Observatory, Fukushima Prefecture, and Okayama Observatory, but only the first three sites detected the occultation.^4: 2 All detections showed that the star faded gradually (lasting up to 1.5 seconds) rather than abruptly during the occultation, revealing that 2002 XV₉₃ had an atmosphere.^154: 2 The discovery was announced on 4 May 2026, making 2002 XV₉₃ likely the first trans-Neptunian object after Pluto discovered to have an atmosphere.^171819d

This object is currently known by its minor planet provisional designation 2002 XV₉₃, given by the MPC upon its discovery.¹² The MPC gave it the minor planet number of 612533 on 28 March 2022.²⁰ As of May 2026, it has not been named.¹ According to naming guidelines by the International Astronomical Union's Working Group for Small Bodies Nomenclature, trans-Neptunian objects classified as plutinos, such as 2002 XV₉₃, should be given mythological names related to the underworld.^21: 8 Since 2002 XV₉₃ received its minor planet number less than 10 years ago, only the discoverer has the privilege of naming it.^21: 6

In an interview with Reuters on 4 May 2026, Arimatsu remarked that the current designation of 2002 XV₉₃ is unmemorable and advocated for a name related to Okinawan mythology, such as Amamikyu (/əˈmɑːmikjuː/).²² Michael E. Brown, who was involved in Palomar Observatory's discovery of 2002 XV₉₃, commented that the object did not get named because it had no known remarkable properties before Arimatsu's discovery of its atmosphere.²³

2002 XV₉₃ orbits the Sun's barycenter with a semi-major axis of 39.3 astronomical units (AU), putting it in the Kuiper belt beyond Neptune's orbit.^16a 2002 XV₉₃ takes 246 years to complete one orbit, which places it in a 2:3 mean-motion resonance with Neptune.^54: 1 For every two revolutions it makes around the Sun, Neptune makes exactly three.²⁵²⁶ It is therefore a member of the plutinos, a large population of trans-Neptunian objects (TNOs) named after its largest member Pluto.^47: 2

2002 XV₉₃'s orbit is elliptical, with an orbital eccentricity of 0.12, and inclined by 13° with respect to the ecliptic.^a Its distance from the Sun ranges from 34.4 AU at perihelion to 44.2 AU at aphelion.^a 2002 XV₉₃ will come to perihelion in March 2070.⁶ Due to gravitational perturbations by the giant planets,^{27: 4 28: 3} the orbital elements of 2002 XV₉₃ vary over time.³ Simulations of 2002 XV₉₃'s orbit show that in 10 million years, its semi-major axis can fluctuate between 39.1–39.9 AU, eccentricity between 0.10–0.15, and inclination between 12.5–13.9°.³

Observations of a stellar occultation in 2024 show that 2002 XV₉₃ has a radius of 235+22
−15 km, or a diameter of 470+44
−30 km, assuming it has a spherical shape.^4: 1 For comparison, 2002 XV₉₃ is about one-seventh the diameter of Earth's moon and about one-fifth the diameter of Pluto.²⁹¹⁷ The mass, bulk density, and shape of 2002 XV₉₃ are unknown, though they can be inferred from those of other similarly-sized TNOs like Huya.^4: 2–3 A 2026 study by Arimatsu and colleagues assumed 2002 XV₉₃ had a bulk density between 1.0 and 1.5 g/cm³, similar to those of Huya and Pluto's moon Charon, respectively.^4: 3, 6 The surface gravity of 2002 XV₉₃ is estimated to be around 100 times weaker than Earth's.²⁹ Arimatsu and colleagues expect that 2002 XV₉₃ has a non-spherical shape due to its relatively small diameter of a few hundred kilometres.^4: 2 The rotation period of 2002 XV₉₃ is unknown and it has not yet been studied via light curves, according to the Asteroid Lightcurve Database.³⁰

Some astronomers, including Noemi Pinilla-Alonso and Michael E. Brown, previously suggested that 2002 XV₉₃ could be theoretically large enough to become spherical and be possibly a dwarf planet, based on a larger diameter estimate from 2012.³¹³²³³ This outdated estimate had 2002 XV₉₃ 549.2+21.7
−23.0 km in diameter, based on mid- to far-infrared measurements of its thermal emission by the Herschel Space Observatory and Spitzer Space Telescope.^74: 1

Measurements of 2002 XV₉₃'s visible brightness and infrared thermal radiation suggest that its surface is dark, with a very low geometric albedo of 0.040+0.020
−0.015.^{7: 13 4: 1} However, this estimate was made in 2012 using a visible-light (V-band) absolute magnitude 5.42±0.46 and thermal emission-derived diameter of 549.2+21.7
−23.0 km.^7: 4 More recent measurements have since found a brighter V-band absolute magnitude of 4.73^28: 5 and a smaller diameter of 470+44
−30 km,⁴ which should indicate a higher albedo for 2002 XV₉₃.^b However, as of May 2026, no peer-reviewed studies have recalculated 2002 XV₉₃'s albedo using newer measurements of its absolute magnitude and diameter.⁴

Telescopic observations in visible light show that the surface color of 2002 XV₉₃ is gray,^g similar to some centaurs and Kuiper belt objects including Achlys and 2004 EW95.^8: 5, 7 Due to 2002 XV₉₃'s great distance from the Sun, its surface temperature averages around 47 K (−226.2 °C; −375.1 °F), cold enough to freeze substances like water into solid ice.⁴

Near-infrared spectroscopy by the James Webb Space Telescope (JWST) has shown that the surface of 2002 XV₉₃ is rich in water ice, in both amorphous and crystalline phases.^34: 3–4 The abundance of water ice in 2002 XV₉₃'s surface is indicated by the presence of absorption bands at wavelengths of 1.5, 2.0, 3.0, and 4.5 μm in the object's near-infrared spectrum, alongside a reflectance peak at 3.1 μm due to crystalline water ice.^34: 4 In the Kuiper belt, crystalline water ice tends to transform into amorphous water ice due to irradiation by cosmic rays, though both phases are expected to be in equilibrium (i.e. amounts of crystalline and amorphous water ice remain constant).^34: 4 2002 XV₉₃ shares its water ice-rich surface composition with other TNOs, including the plutinos 2004 EW₉₅ and 2003 UZ413.^34: 4 These TNOs are classified as "prominent water"-type or "Bowl"-type TNOs, because their near-infrared spectra display a significant bowl-shaped water ice absorption band at the wavelength of 3.0 μm.^359: 4

Besides water, JWST has detected frozen carbon dioxide (CO
₂) on 2002 XV₉₃'s surface.^34: 4 JWST has also detected trace amounts of ¹³CO
₂ (a rare isotopologue of CO
₂).¹¹ In observations from 2022 and 2024, JWST found no signs of hypervolatile compounds such as methane, nitrogen, and carbon monoxide (which can sublimate into gases at 2002 XV₉₃'s temperature).^114: 3–4 The lack of hypervolatiles on 2002 XV₉₃'s surface suggests that most of them had already sublimated and escaped into space.^4: 3–4

In May 2026, a research team led by Ko Arimatsu announced the discovery of a thin atmosphere around 2002 XV₉₃, making it possibly the first TNO after Pluto discovered to have an atmosphere.^17d The atmosphere was inferred from observations of a stellar occultation in January 2024, when 2002 XV₉₃ passed in front of a star and dimmed its light gradually (lasting 1.5 seconds) instead of abruptly, indicating refraction by an atmosphere.¹⁵¹⁶ The gradual disappearance and reappearance of the star was observed to occur within radii of 230 to 270 km (140 to 170 mi) from 2002 XV₉₃'s center.^4: 4 Alternate explanations for this gradual fading, such as a ring system or a shell of dust, are considered unlikely.^184: 2

Based on the observed fading of the occulted star, Arimatsu's team estimated that the atmospheric pressure on 2002 XV₉₃'s surface is between 100 and 200 nanobars—roughly 5 million to 10 million times thinner than Earth's atmosphere and about 50 to 100 times thinner than Pluto's atmosphere,³⁶ but about 100 to 200 times denser than Europa's exosphere.³⁷ At this pressure, 2002 XV₉₃'s atmosphere is dense enough (>0.001 nanobar) that its gas molecules can collide amongst themselves, making it a true atmosphere rather than an exosphere.¹¹ No other TNO besides Pluto is known to have an atmospheric pressure this high.^4: 3 However, it is unclear how the density of 2002 XV₉₃'s atmosphere changes with altitude.¹¹

The composition 2002 XV₉₃'s atmosphere is unknown, and there are competing hypotheses for it.¹¹ One possible composition is methane, a common hypervolatile found in TNOs.⁴ In occultation observations, 2002 XV₉₃'s atmosphere appeared to show a sudden change in refraction at a certain altitude, suggesting that it has a thermal inversion caused by upper-atmospheric heating of trace methane gas (similar to Pluto).^4: 2 However, JWST observed the object after its 2024 occultation and found no signs of methane and carbon monoxide gas, suggesting they do not make up much of its atmosphere.¹¹ If these gases exist over a large altitude range, their partial pressures at 2002 XV₉₃'s surface must be less than 0.0003 nanobars (0.3 picobars).¹¹ However, it remains possible that a low-altitude atmosphere of pure methane could exist.¹¹ Using these JWST observations, a research team headed by Ian Wong proposed that 2002 XV₉₃'s atmosphere could contain either nitrogen, argon, or any other gas that couldn't be detected by JWST.¹¹

The discovery of an atmosphere around 2002 XV₉₃ was unexpected because the object is too small to have a surface gravity strong enough to theoretically hold on to an atmosphere over the age of the Solar System.¹⁵²⁹¹⁶ Physical models predict that 2002 XV₉₃ should lose all of its atmosphere within 100 to 1,000 years via Jeans escape.^154: 3 The present-day existence of 2002 XV₉₃'s atmosphere implies that it was recently replenished, though the cause is unknown.¹⁵ Sublimation of volatile ices on 2002 XV₉₃'s surface is unlikely, because it was not detected in earlier JWST observations.^174: 4 Arimatsu's team hypothesized that 2002 XV₉₃ obtained its atmosphere via either an impact by a hundred-meter-radius comet, or outgassing by cryovolcanic eruptions.^154: 4 These hypotheses can be tested with later observations by occultations: if the atmosphere came from an impact, then its surface pressure should decrease over time, whereas if the atmosphere is sustained by outgassing, then the surface pressure should stay consistent with possibly slow seasonal changes.^194: 4