145451 Rumina

Lore & Background

Rumina was discovered on 9 September 2005 by American astronomers Andrew Becker, Andrew Puckett, and Jeremy Kubica during observations for the Sloan Digital Sky Survey using the 2.5-meter telescope at Apache Point Observatory in Sunspot, New Mexico. The discovery was announced by the Minor Planet Center on 23 July 2006. Precovery observations have been found dating back to November 1976. The object was named after Rumīna, a Roman goddess who protected nursing mothers, with the naming announced by the IAU on 1 September 2025. Its minor planet number 145451 was assigned on 5 December 2006.

Rumina orbits the Sun at distances between 35.1 and 149.7 AU with a semi-major axis of 92.4 AU, taking about 888 years to complete one orbit. Its orbit has a high eccentricity of 0.62 and an inclination of 28.7° to the ecliptic. Both the Minor Planet Center and Johnston's archive classify it as a scattered disc object. In 2018, two stellar occultations were observed: one in February yielding a chord length of 456 km, and another in December suggesting an approximate diameter of 644 km. The object rotates once every 6.71 hours from occultation data, though photometric observations give a synodic period of 9.00±0.06 hours with a light curve amplitude of 0.12±0.05 mag.

Rumina has an absolute magnitude of 4.52±0.01 and a dark grey surface with a V–R color index of 0.33±0.02, indicating a neutral color. Its density is estimated to be >0.56 g/cm³ by Johnston's archive, with a modeled bulk density range of 0.48–0.63 g/cm³ if it is a Jacobi ellipsoid in hydrostatic equilibrium. The minimum density required to prevent breakup from rotation is 0.15 g/cm³. It belongs to the proposed class of mid-sized TNOs between 400 and 1,000 km, which are thought to have highly porous, unheated interiors.

Reader's Guide

Rumina is significant as a large trans-Neptunian object in the scattered disc, a population strongly influenced by Neptune's gravitational perturbations. Its size, estimated from two stellar occultations in 2018, places it in the mid-sized range (400–1,000 km) that scientists believe represents a transition between small, low-density TNOs and larger, high-density dwarf planets. The object's low density estimates (0.48–0.63 g/cm³ from rotational modeling) and high porosity suggest it may have an unheated interior, similar to other mid-sized TNOs like Gǃkúnǁʼhòmdímà. Its dark grey surface and neutral color are consistent with a primitive composition. The well-determined orbit (uncertainty parameter 1) and 548 observations make Rumina a valuable target for understanding the physical properties and dynamical history of scattered disc objects. Its naming after a Roman goddess of nursing mothers adds cultural context to the catalog of minor planets.

Did You Know?

• The object has a diameter of approximately 600 km, based on occultation chords of 456 km and 644 km observed in 2018.
• Rumina's orbit has a semi-major axis of 92.4 AU and takes about 888 years to complete one revolution around the Sun.
• Its surface is dark grey with a low albedo of 0.102 and a neutral V–R color index of 0.33±0.02.