(516977) 2012 HZ84

(516977) 2012 HZ84, provisional designation 2012 HZ84, is a small trans-Neptunian object from the Kuiper belt located in the outermost region of the Solar System, approximately 74 kilometers (46 miles) in diameter. It was discovered on 17 April 2012, by a team of astronomers using one of the Magellan Telescopes in Chile during the New Horizons KBO Search in order to find a potential flyby target for the New Horizons spacecraft.[1] In December 2017, this classical Kuiper belt object was imaged by the spacecraft from afar at a record distance from Earth.[5]

(516977) 2012 HZ84
False-color image of 2012 HZ84 taken by New Horizons in December 2017
False-color image of 2012 HZ84 taken by
New Horizons in December 2017
Discovery[1]
Discovered byNew Horizons KBO Search
Discovery siteLas Campanas Obs.
Discovery date17 April 2012
Designations
(516977) 2012 HZ84
2012 HZ84
TNO[2] · NearScat[3]
cubewano[4] · distant[1]
Orbital characteristics[2]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 4 · 2[1]
Observation arc5.18 yr (1,893 d)
Aphelion55.445 AU
Perihelion37.219 AU
46.332 AU
Eccentricity0.1967
315.38 yr (115,191 d)
321.81°
0° 0m 11.16s / day
Inclination5.4328°
257.02°
86.064°
Physical characteristics
Mean diameter
74 km (est. at 0.09)[4]
8.9[1][2]

    Orbit and classification

    2012 HZ84 orbits the Sun at a distance of 37.2–55.4 AU once every 315 years and 5 months (semi-major axis of 46.33 AU). Its orbit has an eccentricity of 0.20 and an inclination of 5.4° with respect to the ecliptic.[2]

    As a cubewano, also known as classical Kuiper belt object,[4] 2012 HZ84 is located in between the resonant plutino and twotino populations and has a low-eccentricity orbit. It belongs to the "stirred" hot population, but only just, since the rather arbitrary threshold to the cold population is typically defined for inclinations lower than 5°.

    In the object classification of the Deep Ecliptic Survey, however, 2012 HZ84 has a secured SCATNEAR type, which is a combination of the SCAT and NEAR attributes. It means that the object does not cross the orbit of Neptune but has a higher inclination and eccentricity (SCAT) than the survey's CLASSICAL type objects, and it currently interacts with the dominant ice giant Neptune (NEAR), contrary to the much less gravitationally affected objects of the EXTD type.[3]

    The body's observation arc begins with its first observation on 17 April 2012, made by astronomers David Osip, Paul Schechter, David Borncamp, Susan Benecchi and Scott Sheppard of the New Horizons KBO Search (268) team using the Magellan II (Clay) telescope at the Las Campanas Observatory, located in the Atacama desert in Chile.[1][6]

    Milestone image
    Trajectory of New Horizons and other nearby Kuiper belt objects

    When the New Horizons spacecraft imaged 2012 HZ84 in 2017, it was the farthest from Earth ever captured by a spacecraft. The image was taken by the spacecraft's Long Range Reconnaissance Imager (LORRI) on 5 December 2017 at more than 6.12 billion kilometers (40.9 AU) away from Earth. This record was previously held by the Voyager 1 spacecraft which took the iconic Pale Blue Dot image at 6.06 billion kilometers from Earth in February 1990.[5]

    In December 2017, New Horizons also imaged the trans-Neptunian object 2012 HE85, which was first observed by the same team of astronomers the night after they discovered 2012 HZ84.[5] Both objects held this record for little more than one year, until it was superseded on New Year's Eve 2018/19, when New Horizons made its close flyby of 486958 Arrokoth at a new record distance of 6.4 billion kilometers from Earth.[7]

    Numbering and naming

    This minor planet was numbered by the Minor Planet Center on 30 April 2018 and received the number 516977 in the minor planet catalog (M.P.C. 110093).[8] As of 2020, it has not been named.[1]

    Physical characteristics

    According to Johnston's Archive, the object measures 74 kilometers in diameter based on an assumed albedo of 0.09 and an absolute magnitude of 8.9.[2][4] As of 2019, no rotational lightcurve of 2012 HZ84 has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.[2]

    References
    1. "516977 (2012 HZ84)". Minor Planet Center. Retrieved 5 January 2019.
    2. "JPL Small-Body Database Browser: 516977 (2012 HZ84)" (2017-06-23 last obs.). Jet Propulsion Laboratory. Retrieved 5 January 2019.
    3. "Orbit Fit and Astrometric record for 516977". Southwest Research Institute. Retrieved 5 January 2019.
    4. Johnston, Wm. Robert (7 October 2018). "List of Known Trans-Neptunian Objects". Johnston's Archive. Retrieved 5 January 2019.
    5. "New Horizons Captures Record-Breaking Images in the Kuiper Belt". NASA. 8 February 2018. Retrieved 5 January 2019.
    6. Buie, M. W.; Parker, A. H.; Tholen, D. J.; Borncamp, D. M.; Osip, D. J.; Schechter, P. L.; et al. (11 March 2014). "2012 HZ84". Minor Planet Electronic Circular. 2014-E67 (2014-E67 (2014)). Bibcode:2014MPEC....E...67B. Retrieved 5 January 2019.
    7. Wall, Mike (4 January 2019). "The Hunt Is On for Moons Around Ultima Thule". Space.com. Retrieved 5 January 2019.
    8. "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 5 January 2019.

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