The planets Uranus and Neptune exist far out in the solar system beyond Saturn. These two planets are very similar to each other in size, and are smaller than Saturn and Jupiter. Scientists have classified these two planets as “Ice Giants” because they are mostly made of different materials than the “Gas Giants,” Jupiter and Saturn.
Jupiter and Saturn have relatively smaller cores made up mainly of liquid hydrogen and some helium. In contrast, Uranus and Neptune have relatively larger cores made up of a rocky slush of water ice, methane ice and liquid ammonia. The atmospheres of these two Ice Giants are mainly hydrogen and helium with some water, methane and ammonia mixed in. Neptune has an atmosphere that contains more methane, giving the planet a beautiful deep blue color.
Before the Voyager space probes were launched in 1977 very little was known about Uranus and Neptune. They orbit the Sun so far away in the outer solar system that even the best telescopes could not distinguish details on these planets. The Voyager 2 space probe visited Uranus in January of 1986 and then on to Neptune in August of 1989. These two encounters provided the only close-up observations and scientific measurements of these two planets ever obtained. New moons around each planet were discovered, and strange behaviors in their magnetic fields were measured.
Because of the great distances to these two planets, the next available launch windows to send future explorations will not occur until 2030 and 2034.
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