145451 Rumina

Discovery

Rumina was discovered by astronomers Andrew Becker, Andrew Puckett and Jeremy Kubica on 9 September 2005, during observations for the Sloan Digital Sky Survey.^[8][9] The discovery observations were made using the 2.5-meter telescope at Apache Point Observatory in Sunspot, New Mexico.^[9] The discoverers further observed Rumina until November 2005 and found the object in precovery observations from dates as early as October 1999.^[9] The discovery of Rumina was announced by the Minor Planet Center on 23 July 2006.^[9] Since then, Rumina has been found in even earlier precovery observations dating back to November 1976.^[8] Rumina has been observed 548 times, the orbit is well determined with an uncertainty parameter of 1.^[1]

Naming and numbering

The object is named after RumÄ«na, a Roman goddess who protected nursing mothers.^{[10]: 7 } The naming of this object was announced by the International Astronomical Union's Working Group for Small Body Nomenclature on 1 September 2025.^{[10]: 24 } Before Rumina was officially named, it was known by its provisional designation 2005 RM₄₃,^[8] which indicates the year and half-month of the object's discovery date.^[11] Rumina's minor planet catalog number of 145451 was given by the Minor Planet Center on 5 December 2006.^[12] The Kuiper belt objects 145452 Ritona and (145453) 2005 RR43 directly come after Rumina's number in the minor planet catalog.^[12]

Orbital characteristics

Rumina orbits the Sun at a distance of 35.1–149.7 astronomical units (AU) with a semi-major axis or average orbital distance of 92.4 AU once every 888 years (for reference, Neptune's orbit is at 30 AU).^[1][13]

Its orbit has a relatively high eccentricity of 0.62 and an inclination of 28.7° with respect to the ecliptic.^[1]

Classification

Rumina belongs to the scattered disc,^[2] which is a population of TNOs that have distant, inclined, and eccentric orbits that come close to Neptune at perihelion.

The scattered disc population, which includes the dwarf planets Eris and Gonggong, are strongly influenced by Neptune's gravitational perturbations and consequently experience gravitational scattering.^{[14]: 52 }

Both the Minor Planet Center (MPC) and Johnston's archive classify that Rumina is a scattered disc object.^[2][15]

Size

In 2018, two stellar occultations by Rumina were observed on 3 February and 24 December.^[3] The February occultation yielded a single chord length of 456 km (283 mi).^[16] Observations of the December occultation yielded two positive chords, which together suggest an approximate diameter of 644 km (400 mi).^[17] The object rotates on its axis once every 6.71 hours.^[1]

Density theory

Based on its size of 456 and 644 km,^[16][17] it belongs to the proposed class of "mid-sized" TNOs between 400 and 1,000 km (250 and 620 mi) in diameter, which are believed to represent the transition between small, low-density TNOs and large, high-density dwarf planets.^{[18][19]: 1 } Planetary scientists have hypothesized that mid-sized TNOs should have highly porous and unheated interiors, because TNOs in this size range (namely Uni and Gǃkúnǁʼhòmdímà) have been found to have low densities around 1 g/cm³.^[18] Johnston's archive estimate a density of >0.56 g/cm³ for Rumina.^[2]

Surface and spectra

Rumina has an absolute magnitude of 4.52±0.01.^[4] The surface of Rumina is dark grey with low albedo of 0.102 and a V–R color index of 0.33±0.02, which means that it has a neutral color.^[4]