(307261) 2002 MS4

2002 MS₄ imaged by the Hubble Space Telescope on 9 April 2006

(307261) 2002 MS₄ is a large classical Kuiper belt object. It is a possible dwarf planet in the Kuiper belt. It was discovered in 2002 by Chad Trujillo and Michael Brown.

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.

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.

(307261) 2002 MS4 Media

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  2002 MS₄'s position in the constellation Scutum in 2020, moving eastward (left) across the brightest areas of the Milky Way

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  Map showing the location of telescopes that participated in the 8 August 2020 occultation campaign. Telescopes within the path of 2002 MS₄'s shadow (region between the two solid blue curves) made positive detections (blue and red points), whereas telescopes outside the path made negative detections (green points).

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  2002 MS₄'s projected shape revealed by the many positive detection chords from the 8 August 2020 occultation (blue with red error bars). A massive topographic peak and depression is visible along 2002 MS₄'s limb in the northeast direction.

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  2002 MS₄ imaged by the New Horizons spacecraft in July 2016, from a distance of

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  New Horizons trajectory through the Kuiper belt, with positions of nearby KBOs including 2002 MS₄ labeled