21795 Masi

21795 Masi (provisional designation 1999 SN₉) is a Nysian asteroid from the inner regions of the asteroid belt, approximately 3 kilometers (2 miles) in diameter. It was discovered on 29 September 1999, by Italian amateur astronomer Franco Mallia at the Campo Catino Astronomical Observatory in Lazio, Italy.^[1] The likely S-type asteroid has a rotation period of 13.86 hours.^[4] It was named for Italian astronomer Gianluca Masi.^[1]

21795 Masi

Discovery[1]
Discovered by	F. Mallia
Discovery site	Campo Catino Obs.
Discovery date	29 September 1999
Designations
MPC designation	(21795) Masi
Named after	Gianluca Masi[1] (Italian astronomer)
Alternative designations	1999 SN9 · 1988 UE 1993 BZ1
Minor planet category	main-belt[1][2] · (inner) Nysa[3]
Orbital characteristics[2]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc	64.45 yr (23,541 d)
Aphelion	2.8409 AU
Perihelion	1.9222 AU
Semi-major axis	2.3815 AU
Eccentricity	0.1929
Orbital period (sidereal)	3.68 yr (1,342 d)
Mean anomaly	337.35°
Mean motion	0° 16m 5.52s / day
Inclination	1.8376°
Longitude of ascending node	337.09°
Argument of perihelion	81.681°
Physical characteristics
Mean diameter	2.45 km (calculated)[4] 3.150±0.164 km[5][6]
Synodic rotation period	13.862±0.0121 h[7]
Geometric albedo	0.20 (assumed)[4] 0.235±0.037[5][6]
Spectral type	S (assumed)[4]
Absolute magnitude (H)	14.7[6] 14.9[2] 14.970±0.004 (R)[7] 15.41±0.14[8] 15.42[4]

Orbit and classification

Masi is member of the Nysa family (405),^[3] located in the Nysa–Polana complex and one of the largest asteroid families of the asteroid belt, named after 44 Nysa.^[9] It orbits the Sun in the inner main-belt at a distance of 1.9–2.8 AU once every 3 years and 8 months (1,342 days; semi-major axis of 2.38 AU). Its orbit has an eccentricity of 0.19 and an inclination of 2° with respect to the ecliptic.^[2] The body's observation arc begins with a precovery published by the Digitized Sky Survey and taken at the Palomar Observatory in April 1954, more than 45 years prior to its official discovery observation at Campo Catino.^[1]

Physical characteristics

Masi is an assumed, stony S-type asteroid,^[4] which is also the overall spectral type for members of the Nysa family of asteroids.^[9]: 23

Rotation period

In September 2010, a rotational lightcurve of Masi was obtained from photometric observations in the R-band by astronomers at the Palomar Transient Factory in California. Lightcurve analysis gave a rotation period of 13.862 hours with a relatively high brightness amplitude of 0.68 magnitude (U=2).^[7]

Diameter and albedo

According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Masi measures 3.150 kilometers in diameter and its surface has an albedo of 0.235,^[5][6] while the Collaborative Asteroid Lightcurve Link assumes a standard albedo for a stony asteroid of 0.20, and calculates a diameter of 2.45 kilometers based on an absolute magnitude of 15.42.^[4]

Naming

This minor planet was named after Italian astrophysicist and astronomer, Gianluca Masi (born 1972), a researcher and discoverer of minor planets and variable stars, who became an avid amateur astronomer when he was 8 years old.^[1] The official naming citation was published by the Minor Planet Center on 9 May 2001 (M.P.C. 42679).^[10]