2204 Lyyli

2204 Lyyli (prov. designation: 1943 EQ) is a dark asteroid and very eccentric Mars-crosser from the middle region of the asteroid belt, approximately 25 kilometers (16 miles) in diameter. It was discovered on 3 March 1943 by Finnish astronomer Yrjö Väisälä at Turku Observatory in Southwest Finland.^[3]

2204 Lyyli

Shape model of Lyyli from its lightcurve
Discovery[1]
Discovered by	Y. Väisälä
Discovery site	Turku Obs.
Discovery date	3 March 1943
Designations
MPC designation	(2204) Lyyli
Named after	Lyyli Heinänen (Esperantist)[2]
Alternative designations	1943 EQ · 1968 DN
Minor planet category	Mars-crosser[1][3]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	73.75 yr (26,937 days)
Aphelion	3.6435 AU
Perihelion	1.5354 AU
Semi-major axis	2.5894 AU
Eccentricity	0.4071
Orbital period (sidereal)	4.17 yr (1,522 days)
Mean anomaly	350.25°
Inclination	20.561°
Longitude of ascending node	160.45°
Argument of perihelion	283.25°
Earth MOID	0.6872 AU
Mars MOID	0.2547 AU
Physical characteristics
Mean diameter	25.16±2.4 km (IRAS:11)[4] 25.27 km (derived)[5] 27.12±1.31 km[6]
Synodic rotation period	9.51±0.01 h[7] 10 h[8] 11.063±0.001 h[9] 11.09±0.01 h[10]
Geometric albedo	0.020±0.002[6] 0.0232±0.005 (IRAS:11)[4] 0.050±0.006[11] 0.0537 (derived)[5]
Spectral type	SMASS = X[1] · P[11] · X[5]
Absolute magnitude (H)	11.61±0.44[12] · 11.78[5] · 12.1[1] · 12.70[4][6]

Orbit and classification

Lyyli orbits the Sun in the central main-belt at a distance of 1.5–3.6 AU once every 4 years and 2 months (1,522 days). Its orbit has an eccentricity of 0.41 and an inclination of 21° with respect to the ecliptic.^[1]

Naming

This minor planet was named in honour of Lyyli Heinänen (1903–1988), née Hartonen, a Finnish female Esperantist, professor of mathematics, amateur astronomer and former assistant of the discoverer.^[2] The official naming citation was published by the Minor Planet Center on 26 May 1983 (M.P.C. 7944).^[13]

Physical characteristics

Lyyli is an X-type asteroid in the SMASS classification.^[1] It has also been characterized as a P-type asteroid by NASA's NEOWISE mission.^[11]

It has a rotation period of 11 hours^[9] and a very low albedo between 0.02 and 0.05, according to the surveys carried out by IRAS, Akari, and WISE/NEOWISE.^[4][6][11] Other large Mars crossing minor planets include 132 Aethra and 323 Brucia, with diameters of 43 and 36 kilometers, respectively.