Sinope /səˈnoʊpiː/ is a retrograde irregular satellite of Jupiter discovered by Seth Barnes Nicholson at Lick Observatory in 1914,^[1] and is named after Sinope of Greek mythology.

Sinope did not receive its present name until 1975;^[10][11] before then, it was simply known as Jupiter IX. It was sometimes called "Hades"^[12] between 1955 and 1975.

Sinope orbits Jupiter on a high-eccentricity and high-inclination retrograde orbit. Its orbit is continuously changing due to solar and planetary perturbations.^[13] Sinope is believed to belong to the Pasiphae group of retrograde irregular moons.^[14] However, given its mean inclination and different colour, Sinope could be also an independent object, captured independently, unrelated to the collision and break-up at the origin of the group.^[15] The diagram illustrates Sinope's orbital elements in relation to other satellites of the group.

Sinope is also known to be in a secular resonance with Jupiter, similar to Pasiphae. However, Sinope can drop out of this resonance and has periods of both resonant and non-resonant behaviour in time scales of 10⁷ years.^[16]

From measurements of its thermal emission, Sinope has an estimated diameter of 35 km (22 mi).^[7] Sinope is red (colour indices B−V=0.84, R−V=0.46),^[15] unlike Pasiphae, which is grey.

Sinope's infrared spectrum is similar to those of D-type asteroids but different from that of Pasiphae.^[17] These dissimilarities of the physical parameters suggest a different origin from the core members of the group.

• Sinope in fiction