341520 Mors–Somnus

341520 Mors–Somnus (/ˌmɔːrs ˈsɒmnəs/; provisional designation 2007 TY₄₃₀) is a binary and plutino. It consists of two components less than 60 kilometers in diameter, orbiting at a distance of 21000 km.

341520 Mors–Somnus

Discovery[1]
Discovered by	S. S. Sheppard C. Trujillo
Discovery site	Mauna Kea Obs.
Discovery date	14 October 2007
Designations
MPC designation	(341520) Mors-Somnus
Named after	Mors and Somnus (Roman mythology)[2]
Alternative designations	2007 TY430
Minor planet category	TNO[1] · Plutino[3]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 3
Observation arc	6.12 yr (2,235 days)
Aphelion	49.184 AU
Perihelion	28.839 AU
Semi-major axis	39.012 AU
Eccentricity	0.2607
Orbital period (sidereal)	243.67 yr (89,000 days)
Mean anomaly	0.4680°
Mean motion	0° 0m 14.4s / day
Inclination	11.304°
Longitude of ascending node	196.75°
Argument of perihelion	205.32°
Known satellites	1[4]
Physical characteristics
Dimensions	102 km (derived)[4] 175.20 km (calculated)[5] <60 km (each component)[3]
Mass	(7.90±0.21)×1017 kg[3]
Mean density	>0.5 g/cm3[3]
Synodic rotation period	9.28±0.05 h[6]
Geometric albedo	0.10 (assumed)[5] 0.23[3]
Spectral type	B–V = 1.290±0.014[3] V–R = 0.740±0.010[3] V–I = 1.370±0.014[3] C[5]
Absolute magnitude (H)	6.9[1][5] 6.94±0.02[3]

Mors–Somnus was discovered on 14 October 2007, by American astronomers Scott Sheppard and Chad Trujillo with the Subaru Telescope at Mauna Kea Observatories in Hawaii, United States. It was later named after the twins Mors and Somnus from Roman mythology.^[2]

Orbit and binarity

Mors–Somnus is a small double plutino occupying the 3:2 mean motion resonance with Neptune.^[3] The object is a wide optically resolved binary with the following orbital parameters:

Orbital parameters of the Mors–Somnus system^[3]

Semi-major axis, km	Eccentricity	Period, d	Inclination, degree
21000 ± 160	0.1529 ± 0.0028	961.2 ± 4.6	15.68 ± 0.22

The components have almost equal size.

Physical properties

The total mass of the system is 7.90 ± 0.21×10¹⁷ kg. For a realistic minimal density of 0.5 g/cm³ the albedo is >0.17 and the size of the components is <60 km.^[3] The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.1 and calculates a diameter of 175.20 kilometers based on an absolute magnitude of 6.9.^[5]

Mors–Somnus has an ultra-red spectrum in the visible and near-infrared parts of the spectrum. The colors of two components are indistinguishable from each other.^[3] It demonstrates a double-peaked light curve with the period of about 9.28 hours and amplitude of 0.24. This indicates that either primary or secondary has an elongated shape and rotates non-synchronuosly.^[6]

Evolution

The Mors–Somnus system is likely to be an escaped cold classical Kuiper belt object.^[3]

Naming

The minor planet was named after the mythological twin Roman gods of death (Mors) and sleep (Somnus).^[2] The approved naming citation was published by the Minor Planet Center on 2 June 2015 (M.P.C. 94392).^[7]