2002 MS4

## KM size

The Spitzer Space Telescope estimated it to have a diameter of 726±123 km, while the Herschel Space Telescope estimated it to be 934±47 km.

## Ovserving and Most Stuff

2002 MS₄ is a large classical Kuiper belt object and a possible dwarf planet in the Kuiper belt, a region of icy planetesimals beyond Neptune. It was discovered in 2002 by Chad Trujillo and Michael Brown. 2002 MS₄ has been observed 74 times, with precovery images back to 8 April 1954

As of 2019, the rotation period of 2002 MS4 is unknown. Observations in 2005 and 2011 showed possible periods of either 7.33 hours or its alias 10.44 hours (single-peaked), or twice those values for the double-peaked solution, with a small light curve amplitude of 0.05±0.01 mag. Light curve observations of 2002 MS4 are difficult because of the dense field of background stars it is crossing. Observations made in June and July 2011 took advantage of 2002 MS4 moving in front of a dark nebula.

## Moons

2002 MS4 does not have any known moons orbiting it, thus an accurate mass estimate cannot be made.

SO far 2002 MS4 has no discovered moons yet

MOONS=0

## History

2002 MS4 was discovered on 18 June 2002 by Chad Trujillo and Michael Brown at Palomar Observatory. The discovery was announced by the Minor Planet Center on 21 November 2002. In 2007, an archive search revealed the existence of several precovery observations of 2002 MS4, the earliest of which was taken on 8 April 1954, as part of the Digitized Sky Survey at Palomar Mountain. In July 2016, 2002 MS4 was observed by the *New Horizons* spacecraft, as part of its extended Kuiper belt mission. The observations significantly improved the knowledge of 2002 MS4's orbit and phase curve.

As of November 2019, 2002 MS4 has been observed 74 times. It has an observation arc of 64 years.

## Orbit and Classinfacation

2002 MS4 is similar in orbit and current position to Quaoar, although with higher eccentricity and inclination, orbiting every 272.6 years. 2002 MS4 belongs to the class of dynamically hot Kuiper belt objects. It is in an intermittent 18:11 orbital resonance with Neptune.

## Changes Of 2002 MS4

The Spitzer Space Telescope estimated it to have a diameter of 726±123 km, while the Herschel Space Telescope estimated it to be 934±47 km. If the latter case is true, 2002 MS4 would be comparable in size to the dwarf planet Ceres, and would also be the largest Solar System object without a name as of 2020. 2002 MS4 is one of the 10 largest TNOs currently known and large enough to be considered a dwarf planet under the 2006 draft proposal of the IAU. A stellar occultation by 2002 MS4 was observed on 26 July 2019 from British Columbia, with a single chord of 831 km. Another stellar occultation on 19 August 2019 suggested that 2002 MS4 may be highly oblate in shape, with a projected dimension of 842 × 688 km. Another stellar occultation on 8 August 2020, with at least 21 positive detections, resulted in a projected size of 808 × 748 km.

2002 MS4 does not have any known moons orbiting it, thus an accurate mass estimate cannot be made. Based on its size, Brown lists it as nearly certain to be a dwarf planet, however, its low albedo may imply the opposite: dark, mid-sized bodies such as this, less than about 1000 km in diameter and with albedos less than about 0.2, have likely never collapsed into solid bodies, much less differentiated or relaxed into hydrostatic equilibrium, and thus are unlikely to be dwarf planets.

As of 2019, the rotation period of 2002 MS4 is unknown. Observations in 2005 and 2011 showed possible periods of either 7.33 hours or its alias 10.44 hours (single-peaked), or twice those values for the double-peaked solution, with a small light curve amplitude of 0.05±0.01 mag. Light curve observations of 2002 MS4 are difficult because of the dense field of background stars it is crossing. Observations made in June and July 2011 took advantage of 2002 MS4 moving in front of a dark nebula.

## Notes

Prior to February 2020, the scattered-disc object and possible dwarf planet 225088 Gonggong did not have an official name, but was known by its provisional designation 2007 OR10. Until then, 2007 OR10 was the largest unnamed Solar System object.

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