What is Proteus (moon)?
{{Infobox Planet | name = Proteus | image = Proteus (Voyager 2).jpg | bgcolour = #a0ffa0 | discoverer = [[Voyager 2]] <br /> [[Stephen P. Synnott]] | discovered = ~[[June 16]], [[1989]] | epoch = [[18 August]] [[1989]] | semimajor = 117,647 ± 1 [[kilometre|km]] (0.00079 [[Astronomical unit|AU]]) | eccentricity = 0.00053 ± 0.00009 | periapsis = 117,584 ± 10 [[kilometer|km]] | apoapsis = 117,709 ± 10 [[kilometer|km]] | period = 1.12231477 ± 0.00000002 [[day|d]] | avg_speed = 7.623 km/s | inclination = 0.524° (to Neptune equator)<br /> 0.026 ± 0.007° (to local [[Laplace plane]]) | satellite_of = [[Neptune (planet)|Neptune]] | dimensions = 440×416×404 km (± ~15 km) | volume = 3.4 ± 0.3 {{e|7}}[[cubic kilometer|km³]] | mass = ~4.4{{e|19}} [[kilogram|kg]] (estimate) | density = ~1.3 g/cm³ (estimate) | surface_grav = ~0.06 [[Acceleration|m/s<sup>2</sup>]] (0.006 g) | escape_velocity = ~0.16 km/s | rotation = [[synchronous rotation|synchronous]] | axial_tilt = zero | albedo = 0.096 | magnitude = 20.3 | single_temperature = ~51 [[Kelvin|K]] mean (estimate) }} '''Proteus''' or '''Neptune&nbsp;VIII''', is the second biggest [[Natural satellite|moon]] of [[Neptune (planet)|Neptune]], and its biggest close moon. It is named after [[Proteus]], the shape-changing sea god of [[Greek mythology]]. Proteus was found from the images taken by ''[[Voyager 2]]'' probe during the Neptune flyby in [[1989]]. It got the designation '''S/1989&nbsp;N&nbsp;1'''. [[Stephen P. Synnott]] and [[Bradford A. Smith]] said (IAUC 4806) its discovery on [[July 7]], [[1989]], speaking only of “17 frames taken over 21 days”, which gives a discovery date of sometime before [[June 16]]. The name was given on [[16 September]] [[1991]]. Proteus is more than 400 kilometres in diameter, bigger than [[Nereid (moon)|Nereid]], another moon of Neptune. However, it was not found by [[Earth]]-based telescopes because it is so close to the planet that it is lost in the glare of reflected sunlight. Proteus is one of the darkest objects in the [[solar system]].