Cupid

Discovery
Discovered by	Mark R. Showalter and Jack J. Lissauer
Discovery date	August 25, 2003
Designations
Designation	Uranus XXVII
Pronunciation	/ˈkjuːpəd/
Adjectives	Cupidinian/kjuːpɪˈdɪniən/[1]
Orbital characteristics
Semi-major axis	74,392 km
Eccentricity	0.0013
Orbital period (sidereal)	0.618 d
Inclination	0.1° (to Uranus' equator)
Satellite of	Uranus
Physical characteristics
Mean radius	8.9±0.7 km[4]
Surface area	~1,000 km2
Volume	~3,000 km3
Mass	~(1.5–3.5)×1015 kg
Mean density	0.5–1.2 g/cm3[5]
Surface gravity	~0.0013–0.0029 m/s2
Escape velocity	~0.0047–0.0072 km/s
Synodic rotation period	synchronous
Axial tilt	0
Albedo	0.08 (assumed)[2]
Temperature	~64 K

Cupid is an inner satellite of Uranus. It was discovered by Mark R. Showalter and Jack J. Lissauer in 2003 using the Hubble Space Telescope.^[6] It was named after a character in William Shakespeare's play Timon of Athens.^[7]

Cupid is the smallest known inner Uranian satellite (apart from possibly Mab), crudely estimated to be only about 18 km in diameter. This and the dark surface made it too dim to be detected by the Voyager 2 cameras during its Uranus flyby in 1986.

The orbit of Cupid is separated by only 863 km from the orbit of the larger moon Belinda. Unlike Mab and Perdita—two Uranian satellites also discovered in 2003—it does not seem to be perturbed.^[2] Despite this, it has the least stable orbit of Uranus's inner moons—it is likely to collide with Belinda in the next 100,000–10 million years, due to resonance interactions that cause the smaller Cupid to drift into a more dangerous orbit over this timescale.^[5]

Cupid is at most 500 million years old.^[3]

Following its discovery, Cupid was given the temporary designation S/2003 U 2.^[6] It is also designated Uranus XXVII.^[7]

• Hubble Uncovers Smallest Moons Yet Seen Around Uranus – Hubble Space Telescope news release (25 September 2003)