307261 Máni

Lore & Background

Máni was discovered as part of the Caltech Wide Area Sky Survey for Pluto-sized Kuiper belt objects, using Palomar's 1.22-meter Samuel Oschin telescope. It was among the fainter objects detected, with an observed brightness of magnitude 20.9. Follow-up observations occurred on 8 August 2002, and the discovery was announced by the Minor Planet Center on 21 November 2002. Recovery observations in 2003 and precovery images from as early as 8 April 1954 helped refine its orbit.

Máni received its permanent number 307261 on 10 December 2011 and was officially named on 9 June 2025. Its orbit has a semi-major axis of 41.7 AU, eccentricity of 0.15, and inclination of nearly 18°. It is a classical Kuiper belt object with a dynamically 'hot' orbit, possibly in an intermittent 18:11 resonance with Neptune. Máni last passed perihelion in April 1853 and will next do so in June 2123.

Stellar occultations observed from 2019 to 2022 revealed Máni's shape as an oblate spheroid with equatorial diameter 824 ± 20 km and polar diameter up to 770 ± 34 km. The surface is dark gray, composed of water and carbon dioxide ices. Topographic features include a 25 km tall mountain-like peak and a 320 km wide, 45 km deep crater-like depression, among the tallest and deepest known in the Solar System.

Reader's Guide

Máni is significant as one of the largest known trans-Neptunian objects, ranking 10th or 11th in size, and as a candidate dwarf planet. Its extensive occultation campaigns, especially the 8 August 2020 event involving 116 telescope locations across Europe, North Africa, and Western Asia, provided the first clear global shape outline and topography. These observations revealed extreme topographic features—a 25 km peak and a 320 km wide, 45 km deep depression—that are among the most dramatic for any Solar System body. The object's high orbital inclination and possible intermittent resonance with Neptune offer insights into the dynamical history of the Kuiper belt and Neptune's early migration. Its naming in 2025, following the theme of mythological creation figures for classical Kuiper belt objects, connects it to Norse mythology. Máni's unknown mass and density, due to no confirmed moon, leave its dwarf planet status unresolved, highlighting ongoing uncertainties in classifying large Kuiper belt objects.

Did You Know?

• Máni's provisional designation 2002 MS4 was assigned on 21 November 2002.
• The object's surface is dark gray and composed of water and carbon dioxide ices.
• Máni has a mountain-like peak 25 km tall and a crater-like depression 320 km wide and 45 km deep.
• The 8 August 2020 occultation campaign for Máni involved 116 telescope locations, the most extensive for a TNO as of 2023.