Astronomy:(523764) 2014 WC510

Short description: Binary trans-Neptunian object

(523764) 2014 WC₅₁₀

Discovery
Discovered by	Pan-STARRS 1
Discovery site	Haleakalā Obs.
Discovery date	8 September 2011 (first imaged)
Designations
MPC designation	2014 WC510
Minor planet category	plutino · TNO distant · binary
Orbital characteristics
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 2
Observation arc	7.49 yr (2,737 days)
|{{{apsis}}}|helion}}	48.936 AU
|{{{apsis}}}|helion}}	29.535
Semi-major axis	39.236
Eccentricity	0.24724
Orbital period	245.77 yr
Mean anomaly	342.994°
Mean motion	0° 0m 14.437s / day
Inclination	19.542°
Longitude of ascending node	194.464°
|{{{apsis}}}|helion}}	289.173°
Known satellites	1
Physical characteristics
Mean diameter	181±16 km (primary) 138±32 km (secondary)
Geometric albedo	0.051±0.017
Apparent magnitude	22.0
Absolute magnitude (H)	7.2±0.3

(523764) 2014 WC₅₁₀ (provisional designation 2014 WC₅₁₀) is a binary trans-Neptunian object discovered on 8 September 2011 by the Pan-STARRS survey at the Haleakalā Observatory in Hawaii. It was found by Pan-STARRS on 20 November 2014 and was announced later in July 2016 after additional observations and precovery identifications. It is in the Kuiper belt, a region of icy objects orbiting beyond Neptune in the outer Solar System. It is classified as a plutino, a dynamical class of objects in a 2:3 orbital resonance with Neptune. On 1 December 2018, a team of astronomers observed a stellar occultation by the object, which revealed that it is a compact binary system consisting of two separate components in close orbit around each other. The primary and secondary components are estimated to have diameters of around 180 km (110 mi) and 140 km (87 mi), respectively.

Observations

Discovery

Before the announcement of its discovery, 2014 WC₅₁₀ had been observed by the Pan-STARRS survey from 2011 to 2015. All of these observations were made with the Pan-STARRS 1 1.8-meter Ritchey–Chrétien telescope, located at the Haleakalā Observatory atop the Hawaiian island of Maui. The accredited observers using the telescope were B. Gibson, T. Goggia, N. Primak, A. Schultz, and M. Willman. The object was first identified on 20 November 2014, though it was announced later in a Minor Planet Electronic Circular published on 17 July 2016, after additional observations by Pan-STARRS had been found, preceding the team's original observation from 2014. While 2014 WC₅₁₀ is the object's first and only provisional designation assigned by the Minor Planet Center, the date of discovery is considered to be on 8 September 2011, which was the earliest known observation of the object before it was assigned a minor planet number.

Occultation

On 1 December 2018, 2014 WC₅₁₀ occulted a 15th-magnitude double star, blocking out its starlight for a maximal duration of approximately 11 seconds. The stellar occultation was observed by astronomers and citizen scientists across the West Coast of the United States and Canada. Of the 41 participating sites, six of them reported dimmings in the star's brightness, signifying likely positive detections of the occultation. Five of these sites reported two consecutive dimmings due to the occulted star's double nature; 2014 WC₅₁₀ occulted one of the two stars being observed. These observations were part of a campaign coordinated by the Research and Education Collaborative Occultation Network (RECON), a citizen science project dedicated to observing occultations by trans-Neptunian objects.

Prior to the occultation, 2014 WC₅₁₀ had only been observed by Pan-STARRS over an observation arc of 3 years. The calculated orbit from these Pan-STARRS observations had significant uncertainty, which would have been unreliable for predicting occultations. In an effort to reduce the orbital uncertainty, the RECON project collaborated with the Pan-STARRS project to do a precovery search of archival Pan-STARRS images to gather extensive astrometric positions of 2014 WC₅₁₀. Follow-up observations by Pan-STARRS were also conducted through 2016–2018 and helped extend 2014 WC₅₁₀'s observation arc to 6.3 years. Although an observation arc of this length is generally unreliable for predicting occultations especially by distant objects, this was compensated by Pan-STARRS's highly accurate astrometric system, allowing for 2014 WC₅₁₀'s orbital uncertainty to be significantly reduced.

Orbit and classification

2014 WC₅₁₀ is classified as a plutino, a subgroup of the resonant trans-Neptunian objects located in the inner region of Kuiper belt. Named after the group's largest member, Pluto, the plutinos are in a 2:3 mean-motion orbital resonance with Neptune. That is, they complete two orbits around the Sun for every three orbits that Neptune takes. 2014 WC₅₁₀ orbits the Sun at an average distance of 39.24 astronomical units (5.87×10⁹ km; 3.65×10⁹ mi), taking 245.8 years to complete a full orbit. This is characteristic of all plutinos, which have orbital periods around 250 years and semi-major axes around 39 AU.

Like Pluto, 2014 WC₅₁₀'s orbit is elongated and inclined to the ecliptic. 2014 WC₅₁₀ has an orbital eccentricity of 0.25 and an orbital inclination of 19.5 degrees with respect to the ecliptic. Over the course of its orbit, 2014 WC₅₁₀'s distance from the Sun varies from 29.5 AU at perihelion (closest distance) to 48.9 AU at aphelion (farthest distance). 2014 WC₅₁₀ has last passed aphelion in the early 20th century, and is now moving closer to the Sun, approaching perihelion by 2032. Simulations by the Deep Ecliptic Survey show that 2014 WC₅₁₀ can acquire a perihelion distance (q_min) as small as 28.7 AU over the next 10 million years.

Binary system

Comparison of mean separation distances and diameters of tight trans-Neptunian binaries including 2014 WC₅₁₀

Observations of the December 2018 occultation revealed that 2014 WC₅₁₀ is a compact binary system consisting of two separate components in close orbit around each other. Of the six sites that reported positive detections of the occultation, one site located in Bishop, California, detected a shorter dimming event separate from the main detections by the other five sites located south of it. A 2020 study led by Rodrigo Leiva and Marc Buie analyzed the occultation data and determined that the detection from Bishop was most likely an occultation by a secondary component of 2014 WC₅₁₀.

Since the two components were only observed for a short period of time during the occultation, the binary system's orbital parameters have not been determined. The projected separation distance between the primary and secondary is 349 ± 29 km (217 ± 18 mi), derived from an angular separation of 16±1 milliarcseconds. Assuming a density of 1 g/cm³ for both components, their mutual orbital period would likely be under one day. 2014 WC₅₁₀ has the third-smallest observed component separation of all known binary TNOs (As of 2021), after 2011 JY31 and 2014 OS393. Such tight binary TNOs are difficult to resolve with direct imaging due to their characteristic small separation distances between their components.

Most models of the formation of the Solar System indicate that most TNOs have formed as binaries, hence they are expected to be common especially in the Kuiper belt population. While most known binary TNOs appear to have wide mutual orbits, tight binary TNOs similar to 2014 WC₅₁₀ are thought to have a higher chance of survival after their formation. 2014 WC₅₁₀ belongs to the population of smaller TNOs, which are expected to have a primordial origin similar to the classical Kuiper belt object 486958 Arrokoth.

Physical characteristics

Assuming a circular projected shape for the components' occultation profiles, the diameters of the primary and secondary are estimated to be 181 ± 16 km (112.5 ± 9.9 mi) and 138 ± 32 km (86 ± 20 mi), respectively. The diameter ratio of the secondary to the primary is 0.76:1.00—the secondary component is approximately 75% as large as the primary. Since the mutual orbit of the components is undetermined, the mass and density of the 2014 WC₅₁₀ system cannot be derived. The individual components of the 2014 WC₅₁₀ system are among the smallest trans-Neptunian objects with sizes measured with stellar occultations, following the Kuiper belt object 486958 Arrokoth (~30 km).

Given the components' estimated diameters and their combined absolute magnitude of 7.2, their calculated geometric albedos indicate that they have dark surfaces, reflecting about 5% of incident visible light. However, the estimated geometric albedo may be subject to a systematic error depending on the true shapes and photometric properties of the components, resulting in a significant uncertainty of ±2%. Nonetheless, 2014 WC₅₁₀ is one of the darkest objects measured with stellar occultations, being darker than 486958 Arrokoth.

Numbering and naming

This minor planet was numbered by the Minor Planet Center on 25 September 2018 and received the number 523764 in the minor planet catalog. As of 2020, it has not been named.

External links

• SwRI study describes discovery of close binary trans-Neptunian object, 28 September 2020, Southwest Research Institute
• A stellar occultation by a small plutino with RECON, Rodrigo Leiva et al., September 2019, Europlanet Science Congress–Division for Planetary Sciences Joint Meeting 2019
• Tight and contact TNO binaries with stellar occultations, Marc W. Buie et al., 2019
• (523764) 2014 WC510, Wm. Robert Johnston, Asteroids with Satellites Database—Johnston's Archive, 11 October 2020
• (523764) 2014 WC510 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters