(208996) 2003 AZ84

(provisional designation ) is a trans-Neptunian object with a possible moon located in the outer regions of the Solar System. It is approximately 940 kilometers across its longest axis, as it has an elongated shape. It belongs to the plutinos – a group of minor planets named after its largest member Pluto – as it orbits in a 2:3 resonance with Neptune in the Kuiper belt. It is the third-largest known plutino, after and . It was discovered on 13 January 2003, by American astronomers Chad Trujillo and Michael Brown during the NEAT survey using the Samuel Oschin telescope at Palomar Observatory.

Though elongated in shape, displays a small lightcurve amplitude due to its rotation axis being oriented nearly pole-on; the variability is mainly caused by albedo features on its surface.

It is considered a very likely dwarf planet by astronomers Gonzalo Tancredi and Michael Brown. However, Will M. Grundy et al. conclude that objects such as this, in the size range of 400–1,000 km, with albedos less than ≈0.2 and densities of ≈1.2 g/cm³ or less, have likely never compressed into fully solid bodies, let alone differentiated or collapsed into hydrostatic equilibrium, and so are highly unlikely to be dwarf planets.

Physical characteristics

The Spitzer Space Telescope has estimated its size at , while an analysis of a combination of Spitzer and Hershel data yielded a slightly higher estimate of . These results are in agreement with each other.
The large size of makes it a possible dwarf planet. However, if one assumes it to be in hydrostatic equilibrium, the density that results is too low for it to be solid, and hence it may not be a dwarf planet. Its mass is unknown since the satellite has not been recovered.

A stellar occultation in 2010 measured a single chord of . But this is only a lower limit for the diameter of because the chord may not have passed through the center of the body.

In 2017, stellar occultations and data from its rotational lightcurve suggested that had an elongated shape, presumably due to its rapid rotation rate of 6.71 hours, similar to Haumea and Varuna. That would give approximate dimensions of 940×766×490 km, with its longest axis nearly twice as long as its polar axis.

The spectra and colors of are very similar to those of Orcus, another large object in 2:3 resonance with Neptune. Both bodies have a flat featureless spectrum in the visible and moderately strong water ice absorption bands in the near-infrared, although has a lower albedo. Both bodies also have a weak absorption band near 2.3 μm, which may be caused by ammonia hydrate or methane ice.

Orbit and rotation

orbits the Sun at an average distance of 39.4 astronomical units (AU) and completes a full orbit in 247 years. It is in a 2:3 orbital resonance with Neptune; completes two orbits around the Sun for every three orbits completed by Neptune. Since it is in a 2:3 resonance with Neptune, is classified as a plutino. Its orbit is inclined to the ecliptic by 13.6 degrees. The orbit of is moderately eccentric, with an orbital eccentricity of 0.183. , is currently located from the Sun. It had approached its aphelion (furthest distance from the Sun) in 1982 and will come to its perihelion (closest distance to the Sun) in 2107. Simulations by the Deep Ecliptic Survey show that over the next 10 million years will not come closer (''q_min'') than 31.6 AU from the Sun (it will stay farther away than Neptune).

The rotation period of this minor planet was first measured by Scott Sheppard in 2003. Light curves obtained by Sheppard at the University of Hawai'i's 2.2-meter telescope gave an ambiguous rotation period of either 6.71 or 13.42 hours, with a brightness variation of 0.14 magnitudes (). The shorter rotation period refers to the single-peaked solution, expected if the brightness variations resulted from albedo spots. The longer rotation period is for a double-peaked solution, more consistent with an elongated shape that is rotating edge-on.

Satellite

Using observations with the Hubble Space Telescope, the discovery of a satellite of was reported in IAUC 8812 on 22 February 2007. The object was measured with a separation of 0.22 arcsec and an apparent magnitude difference of 5.0. , attempts to recover the satellite have failed. The unrecovered satellite is estimated to be about in diameter.

Notes

References

External links

(208996) 2003 AZ84 Precovery Images


– ''Minor Planet Center''
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{{DEFAULTSORT:208996
Plutinos
Discoveries by Michael E. Brown
Discoveries by Chad Trujillo
Possible dwarf planets
(208996) 2003 AZ84
Binary trans-Neptunian objects
Objects observed by stellar occultation
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