Galatea

Galatea
Discovery Information
Discoverer	Stephen P. Synnott and Voyager Imaging Team (Voyager 2)
Discovery Date	1989.07
Discovery Method	Direct imaging
Physical Properties
Type	Dwarf moon
Class	Frigid asteroid
Diameter	1495.18 km
Mass	8.4055·10⁻⁵ M☾
Solar Day	10ʰ17ᵐ23.82ˢ
Orbital Period	10ʰ17ᵐ23.56ˢ
Surface Conditions
Temperature	-222 °C (51 K; -367 °F)
Gravity	0.0098642 g

Overview

Galatea, additionally referred to as Neptune VI or by its temporary designation S/1989 N 4, is the fourth-closest known natural satellite orbiting Neptune. It's the 5th largest known Neptunian moon, and it's named after Galatea, one of the Nereids in Greek mythology. It formed in a similar process that the other inner moons of Neptune were gone through by a debris disc around Neptune, which would later dissipate to form the inner moons after Triton decimated the previous larger natural satellites of Neptune. Its orbit lies below the synchronous orbit radius of Neptune; this causes Galatea's orbit to gradually go closer to the planet due to tidal dissipation. It will either break up into smithereens and integrate into part of Neptune's ring system by crossing the Roche limit or disintegrate into the Neptunian atmosphere.

Discovery

In late July 1989, the Voyager Imaging Team discovered three unidentified natural satellites (which were later identified as Despina, Galatea, and Larissa) orbiting Neptune, taken by the Voyager 2 probe during its flyby of the planet. The moon wasn't given a proper name yet, as it had only been given a provisional designation of S/1989 N 4. The discovery of S/1989 N 4 was announced on 2 August 1989, and Galatea was given a proper name approved by the IAU on 16 September 1991.

Physical characteristics

Galatea has a diameter measuring 130.46 km across, and it is irregularly shaped as a result of its miniscule size, like the other inner Neptunian moons. The moon was formed through a process known as accretion, and Galatea used to lie inside the former debris disc around Neptune that Galatea accreted mass over. This was created when the newly captured moon, Triton, was held onto an elliptical orbit, destroying the original moons of Neptune in the process and, as a result, leaving a disc of debris.

Motion

Galatea completes its orbit around Neptune every 10 hours and 17 minutes and maintains an average distance to Neptune of about 61,953 km. Galatea orbits just inside the Adams ring and acts like a shepherd, keeping the ring particles into a narrow span where the Adams ring lies through a 42:43 outer Lindblad resonance and thus maintaining the ring. Galatea may produce the ring arcs on the Adams ring caused by Galatea's gravitational influence, although numerous orbital resonances between the Adams ring particles and Galatea may play a role in maintaining the ring arcs. Galatea's influence on the Adams ring has also been used to calculate its mass, which is about 1.94×10¹⁸ kilograms. Galatea is probably in a spin-orbit rotation with Neptune, with the same side of Galatea facing the planet and the other side facing away.

Gallery

Galatea and Despina shepherds Adams and Le Verrier ring

Galatea's presumed surface