2014 OS393

2014 OS₃₉₃
	2014 OS393 imaged by the New Horizons spacecraft on 5 January 2019
Discovery
Discovered by	New Horizons KBO Search
Discovery site	Hubble Space Telescope
Discovery date	30 July 2014
Designations
MPC designation	2014 OS393
Alternative designations	e31007AI · e3 · PT2
Minor planet category	TNO · cubewano; distant · binary
Orbital characteristics
	Epoch 8 August 2014 (JD 2456877.5)
	Uncertainty parameter 8
Observation arc	121 days
Aphelion	45.350 AU
Perihelion	42.534 AU
Semi-major axis	43.942 AU
Eccentricity	0.0320
Orbital period (sidereal)	291.29 yr (106,394 d)
Mean anomaly	60.464°
Mean motion	0° 0m 12.24s / day
Inclination	3.8151°
Longitude of ascending node	138.21°
Argument of perihelion	78.660°
Physical characteristics
Mean diameter	30 km (component); 42 km (effective)
Synodic rotation period	36.214 h (1.5089 d)
Geometric albedo	0.04–0.10; 0.04–0.15
Spectral type	V–I = 1.18
Apparent magnitude	25.8
Absolute magnitude (H)	10.1; 10.111

2014 OS₃₉₃, unofficially designated e31007AI, e3 and PT2, is a binary trans-Neptunian object in the classical Kuiper belt, the outermost region of the Solar System. It was first observed by the New Horizons KBO Search using the Hubble Space Telescope on 30 July 2014.^[1] Until 2015, when the object 486958 Arrokoth was selected, it was a potential flyby target for the New Horizons probe.^[3] Estimated to be approximately 42 kilometres (26 mi) in diameter,^[5] the object had a poorly determined orbit as it had been observed for only a few months.^[4] With MPEC 2024-E99 the Minor Planet Center published on 6 March 2024 additional observations by New Horizons KBO Search-Subaru which allowed to compute a fairly reliable orbit.

Discovery and designation

2014 OS₃₉₃ was discovered by the New Horizons Search Team with the help of the Hubble Space Telescope^[11] because the object has a magnitude of 26.3, which is too faint to be observed by ground-based telescopes. Preliminary observations by the HST searching for KBO flyby targets for the New Horizons probe started in June 2014, and more intensive observations continued in July and August.^[12]^[13] 2014 OS₃₉₃ was first discovered in observations on July 30, 2014, but it was designated e31007AI at the time, nicknamed e3 for short.^[3]^[8] Its existence as a potential target of the New Horizons probe was revealed by NASA in October 2014^[14]^[15] and designated PT2, but the official name 2014 OS₃₉₃ was not assigned by the Minor Planet Center until March 2015 after better orbit information was available.^[3]

Orbit and classification

2014 OS₃₉₃ is a trans-Neptunian object and likely a non-resonant classical Kuiper belt object, also known as "cubewano".^[5] It orbits the Sun at a distance of 43.3–44.84 AU once every 292 years (semi-major axis of 44.04 AU). Its orbit has an eccentricity of 0.018 and an inclination of 3.8° with respect to the ecliptic.^[4] As this object has not been observed since July 2017, its orbit remains rather poorly determined still containing a high uncertainty of 7.^[1]^[4]

The body's observation arc begins with a precovery taken on 25 June 2014, by the New Horizons KBO Search team using the Subaru Telescope at Mauna Kea Observatory on Hawaii.^[1] and ends presently on 21 July 2017, covering 1122 days.

Binary

After the New Horizons probe completed its flyby of Arrokoth, the probe began observations of other nearby surrounding Kuiper belt objects, including 2014 OS₃₉₃. Observations of 2014 OS₃₉₃'s brightness variations at high phase angles allowed the New Horizons probe to make a rough determination of its rotation period as well as its shape. As New Horizons observed 2014 OS₃₉₃ at phase angles near 90°, it displayed large variations in brightness, indicating that its shape is either extremely elongated or 2014 OS₃₉₃ could be a binary system of two separated components. 2014 OS₃₉₃ appeared to be possibly a separated binary in a few resolved New Horizons images, but in 2020 this remained inconclusive.^[16]

Later work by Hal Weaver in 2021 showed that 2014 OS₃₉₃ is indeed a binary, with two components about 30 km (19 mi) in diameter, about 150 km (93 mi) apart.^[17]^[7]

Exploration

After the New Horizons probe completed its flyby of Pluto, the probe was to be maneuvered to a flyby of at least one Kuiper belt object. Several potential targets were under consideration for the first such flyby. 2014 OS₃₉₃ has an estimated mean diameter between 30 and 55 kilometers, depending on the body's assumed albedo.^[5]^[8] The potential encounter in 2018–2019 would have been at a distance of 43–44 AU from the Sun.^[2]

On 28 August 2015, the New Horizons team announced the selection of 2014 MU₆₉ (later named 486958 Arrokoth) as the next flyby target, eliminating the other possible targets — 2014 OS₃₉₃, 2014 PN70, and 2014 MT69.^[3]^[18]^[19]

The spacecraft passed 2014 OS₃₉₃ in January 2019, at a distance of less than 0.1 AU (15 million km, 9.3 million miles). This makes 2014 OS₃₉₃ the second closest KBO observed by New Horizons, after Arrokoth.^[20]