Sinope , also known as Jupiter IX, is one of the outermost irregular satellites of Jupiter.
Discovery and Naming Sinope was discovered by Seth Barnes Nicholson at Lick Observatory in 1914. It 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.
Orbit Sinope orbits Jupiter at an average distance of 23.6 million km in 742 days, at an inclination of about 159° to the ecliptic, in a retrograde direction and with an eccentricity of 0.269. Its orbit is continuously changing due to solar and planetary perturbations. Sinope belongs to the Pasiphae group, a group of retrograde moons of Jupiter with semi-major axes spread over 22–25 million km, inclinations between 141° and 158°, and higher eccentricities between 0.22 and 0.44. 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.
Physical characteristics
From measurements of its thermal emission, Sinope has an estimated diameter of about 35 kilometers and a visible light albedo of 4.2%. Sinope is pale red in color (colour indices 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. Furthermore, a measured low beam value of 0.82 ± 0.02 indicates that Sinope has considerable surface roughness. The rotation period was found to be approximately 13 hours and 9,6 minutes with a peak amplitude of about ~0.2 magnitudes. The rotation period was regarded by a later paper as uncertain due to the short observation periods.
Origin Sinope probably did not form near Jupiter but was captured by Jupiter later. Like the other members of the Pasiphae group, which have similar orbits, Sinope is probably the remnant of a broken, captured heliocentric asteroid. 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. Aoede, a small irregular moon of Jupiter, has a similar orbit to Sinope and could be a remnant of the latter.
See also Sinope in fiction
References
External links Sinope Profile by NASA's Solar System Exploration David Jewitt pages Jupiter's Known Satellites (by Scott S. Sheppard) Ephemeris IAU-MPC NSES
