Neptune & its moon Triton

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Credit: NASA

Another fantastic image from the Voyager 2 spacecraft.

This one is of the dark side of Neptune with its largest moon Tritan and was taken just after Voyager 2’s closest approach to Neptune, the 8th & outermost planet in the solar system in 1989.

Neptune resides in an orbit of 4,504,000,000 km or some 30 astronomical units (AU) from the Sun (the Earth’s orbit is one AU) and it orbits the Sun once every 165 years.

It has a diameter of just under 50,000km and a mass some 15x that of the Earth.

Neptune is often referred to as an ‘ice giant’ and is in some ways similar in characteristics to Uranus in that it is largely comprised of ‘ices’ and rock at its core. This is believed to be surrounded by a mantle of water, ammonia and methane and an atmosphere predominantly of hydrogen, helium and methane.

Winds in the atmosphere can reach speeds up to 1100km/hour and are the fastest known winds in the solar system, the reasons for which are not clear.

Interestingly,  Neptune radiates more than twice the energy than it receives from the Sun alone and therefore must have its own internal heat source.

Neptune’s magnetic field is also rather strange also, being off centre and at a 60 degree angle to its rotation axis, and the internal processes that generate this unusal field are uncertain.

Neptune was discovered in 1846 by observation at the predicted location of the planet calculated through the study of the perturbations of the orbit of Uranus.