(208996) 2003 AZ84 - 17th Largest TNO? 3rd Largest Plutino ?

(208996) 2003 AZ84, is a plutino, like Pluto, in a 2:3 resonance with Neptune. 2003 AZ84 is possibly the 17th largest TNO and 3rd largest Plutino currently known.

Discovery

2003 AZ84 was discovered on January 13, 2003 by Michael E. Brown and Chadwick A. Trujillo using the Samuel Oschin telescope in the Palomar Observatory.

Stats

Estimated Diameter: 685 km (686 ± 96 km)
Aphelion: 46.48 AU
Perihelion: 32.61 AU
Semi-major axis: 39.56 AU
Orbital Period: 248.81 years
Rotation period: 13.42 hours
Date discovered: 2003.1.13
Satellite: 1 ?
Classification: TNO, KBO - Plutino

Orbit

2003 AZ84 is classified as a plutino, which means that it is in a 3:2 orbital resonance with Neptune, similar to that of Pluto. It orbits the Sun in just over 248 Earth years.

2003 AZ84 is currently 45.3 AU from the Sun and came to aphelion (farthest distance from the Sun) in 1982. It will come to perihelion in 2107.

Physical characteristics

The Spitzer Space Telescope has estimated 2003 AZ84 to have a size of 686 ± 96 km, while an analysis of a combination of Spitzer and Hershel data yielded a somewhat higher estimate of 910 ± 60 km.

The spectra and colors of 2003 AZ84 are very similar to those of Orcus, another large planetoid in 3:2 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 2003 AZ84 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.

A stellar occultation in 2010 measured a single chord of 573 ± 21 km. But this is only a lower limit for the diameter of 2003 AZ84 as the chord may not have passed through the center of the body.

Satellite

Using observations with the Hubble Space Telescope, the discovery of a satellite of 2003 AZ84 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.

As of 2012, attempts to recover the satellite have failed. The unrecovered satellite is estimated to be about 68 ± 20 km in diameter.

How big is it?

2003 AZ84 is so far away in the outer solar system that we don't know for sure how large it is. Because all we see is a dot of light, which is sunlight reflected off the surface of the TNO. But we don't know if the object is bright because it is large or if it is bright because it is highly reflective or both.