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

Sinope did not receive its present name until 1975; before then, it was simply known as Jupiter IX. It was sometimes called "Hades" 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. Sinope is believed to belong to the Pasiphae group of retrograde irregular moons. 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. 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.

From measurements of its thermal emission, Sinope has an estimated diameter of 35 km (22 mi). Sinope is pale red in color (colour indices V=18.63 B−V=0.84, R−V=0.46), and it falls under the light red color-class, comparable to P-type asteroids and D-type asteroids. This sets it apart from Pasiphae, which is closer to C-type asteroids.

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