Nereid is only about 340 kilometers (210 miles) in diameter and is soДЇar from Neptune that it requires 360 days to make one orbit вЂ“ only five days In 1949, astronomer Gerard Kuiper discovered Nereid, the second of NeptuneвЂ™sД®scorts. Some astronomers to surmise that Neptune had captured Triton as it traveled In a direction opposite to the rotation of the planet. Satellite in the solar system to circle a planet in a retrograde direction вЂ“ Triton, almost the size of EarthвЂ™s Moon, is the only large Scarcely a month after Galle and dвЂ™Arrest first saw Neptune, BritishДЄstronomer William Lassell spotted a satellite orbiting the planet and named Planet.) Still, any knowledge and understanding of Neptune was limited by theДЄstronomerвЂ™s ability to see the distant object, almost 4.5 billion kilometers Of observing Jupiter, in January 1613, but didnвЂ™t realize he was seeing a new (Galileo Galilei had seen Neptune during several nights Similar predictions were made independentlyД«y John Couch Adams. Student, discovered the eighth planet on the basis of mathematical predictionsД«y Urbain Jean Joseph Le Verrier. Gottfried Galle, of the Berlin Observatory, and Louis dвЂ™Arrest, an astronomy Years, until their nuclear power sources can no longer supply enoughД®lectrical energy to power critical subsystems.ДЄstronomers have studied Neptune since September 23, 1846, when Johann We will be able to communicate with the two spacecraft for another 25 to 30 The solar system, diving below the ecliptic plane at an angle of about 48Дegrees and a rate of about 470 million kilometers a year.Д«oth spacecraft will continue to study ultraviolet sources among the stars,ДЄnd their fields and particles detectors will continue to search for theД«oundary between the SunвЂ™s influence and interstellar space.

Voyager observed Neptune almostД¬ontinuously from June to October 1989. Second (about 42,000 miles an hour) to reach Neptune, which is 30 timesДЇarther from the Sun than Earth is.

Voyager 2 traveled 12 years at an average velocity of 19 kilometers a.

Voyager 2, launched August 20, 1977, visited Jupiter in 1979, Saturn in 1981ДЄnd Uranus in 1986 before making its closest approach to Neptune on August 25,

It is now leaving the solar system, rising above the ecliptic plane atДЄn angle of about 35 degrees, at a rate of about 520 million kilometers a.

Voyager 1, launched September 5, 1977, visited Jupiter in 1979 and Saturn in Giant planets, 48 of their moons, and their unique systems of rings and Between them, these spacecraft have explored four Voyager 2 is one of twin spacecraft launched more than a decade ago to explore Substantial amounts of hydrogen and helium with traces of other gases. They have no solid surfaces but possess massive atmospheres that contain These planets are about 4 to 12 times greater in diameter than Earth. вЂ“ known as gas giants the others in this class are Jupiter, Saturn and Neptune is one of the class of planets вЂ“ all of them beyond the asteroid belt Triton, the last solid body the spacecraft will have an opportunity to study. Passed about 40,000 kilometers (25,000 miles) from NeptuneвЂ™s largest moon, To any planet since leaving Earth 12 years ago. (3,000 miles) above NeptuneвЂ™s north pole, Voyager 2 made its closest approach The planet Neptune, its final planetary target. In the summer of 1989, NASAвЂ™s Voyager 2 became the first spacecraft to observe

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