Proteus

Proteus
Discovery Information
Discoverer	Voyager 2 (Stephen P. Synnott and Bradford A. Smith)
Discovery Date	1989.07.01
Discovery Method	Direct imaging
Physical Properties
Type	Moon
Class	Frigid asteroid
Diameter	435.58 km (0.034183 D⊕)
Mass	0.00068038 M☾
Solar Day	26ʰ56ᵐ09.83ˢ
Orbital Period	26ʰ56ᵐ08.01ˢ
Surface Conditions
Temperature	-220.13 °C
Gravity	0.0071625 g

Overview

Proteus (also known as Neptune VIII) is the second largest Neptunian moon and 20th-largest moon in our Solar system. It orbits right at Neptune's equator in a low eccentricity. Proteus is composed mostly of ice and it's 435.58 km (270.65 mi) in diameter. Proteus possibly have formed by a re-accretion from the fragments from Neptune's previous major moons not long after Triton is gravitationally captured by Neptune. Proteus is named after the shapeshifting sea god Proteus from Greek mythology. It's shape is more or less like a polyhedron with some visible irregularities and it is heavily bombarded with impact craters with the largest one called Pharos.

Discovery

Proteus was discovered by the Voyager 2 spacecraft after taking images of the Neptunian moon system two months before Voyager 2's flyby of Neptune on 25th of August, 1989. It is the third Neptunian moon to be discovered and unusually, a smaller, outer Neptunian moon, Nereid is the second Neptunian moon to be discovered from a ground-based observatory, meaning that Nereid was discovered 33 years earlier than Proteus, Proteus probably failed to be observed from Earth owing to its great distance from Earth and its dark appearance. Proteus received its temporary designation S/1989 N 1 just after its discovery. Stephen P. Synnott and Bradford A. Smith made known the discovery of Proteus on 7th of July, 1989. The moon received its new name approved by the IAU on 16th of September, 1991 and it is named after the shapeshifting sea god Proteus in Greek mythology.

Motion

The orbital period is almost the same as Earth's rotational period at around 26 hours, and Proteus orbits Neptune at an average distance of 117,646 km. Both the eccentricity and inclination of Proteus's orbit is low as the orbital eccentricity of Proteus is around 0.001 and the orbital inclination of Proteus is 1°05'. Proteus possibly on one occasion once been a part of a 1:2 orbital resonance with a smaller, inner moon, Larissa but by the effect of Proteus slowly moving outwards by tidal migration, over a few hundred million years, Proteus and Larissa are no longer in orbital resonance. It is evident that Proteus is tidally locked with Neptune with the one hemisphere always facing Neptune and the other facing away.

Proteus is currently in an almost 11:13 mean-motion resonance with another Neptunian moon, Hippocamp but Proteus is being tidally migrating faster than Hippocamp due to its higher mass and in result, Proteus is calculated to retreat from Neptune at about 40 km (24 mi) in the next 18 million years, at this specific future time frame, Proteus will enter an accurate 11:13 orbital resonance with Hippocamp.

Features and Physical structure

Proteus does not show an indication of geologic modification due to its small size, it is heavily bombarded by impact craters and there are network of extensive streaks of scarps, valleys, and grooves with a most notable linear features going parallel to the equator to the west of Pharos. These streaks may have originate from enormous craters and powerful tidal forces from Neptune.

Pharos

Proteus has only one named surface feature and it is called Pharos, the impact crater features a depth that measures around 10-15 km (6-9 mi) and a diameter around 230-260 km (142-161 mi), more than half the diameter of Proteus alone. Pharos is formed by a cometary collision with Proteus, the collision also may have produced the second-smallest moon of Neptune called Hippocamp due to how close Hippocamp is from Proteus, this would also classify the tiny moon as a third-generation moon because it is formed from a second-generation moon. The crater received its name on 1994 and it is named after the Pharos of Alexandria.

Shape

Proteus's shape is proximate to a sphere but not quite with a diameter measuring 435 km (270 mi), it is the largest irregularly shaped object in the Solar system and, the shape of Proteus is more like an asymmetrical polyhedron than triaxial ellipsoid. Proteus thought to be not far from the limit of how large a celestial body can be without turning into a sphere by its own gravity, despite this, Mimas is more spherical than Proteus even though Mimas is smaller and less massive than Proteus in comparison, this is may in cause by the elevated temperature close to Saturn or tidal flexing.

Origin

Proteus and the inner moons of Neptune are formed from a debris disk after Triton is gravitationally captured by Neptune, during that time, Triton was orbiting in a high eccentric orbit, this orbit combined with a strong gravitational pull of Triton causes the original Neptunian moon system to destabilize, resulting with tons of collisions and ejections and eventually producing a debris disk where the current, second-generation moons like Proteus can accrete material from the debris disk. The debris disk is also be the cause of Triton's orbital eccentricity being low. Proteus was previously closer to Neptune than the present day and it probably formed closer to Neptune, during that time, young Proteus is thought to orbit around Neptune at about 8,000 km (5,000 mi) less than the current distance between Proteus and Neptune, the outward migration of Proteus is caused by tidal interactions with Neptune, when Proteus migrated outwards, collision events with Proteus occurred, producing sizable impact craters.

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