Planet Neptune — Reading Comprehension Lesson

Reading Passage

Planet Neptune

Neptune is the eighth and farthest planet from the sun in our solar system. It orbits the sun at an average distance of about 2.8 billion miles — roughly 30 times farther from the sun than Earth. At that distance, sunlight takes about four hours to reach Neptune, compared to about eight minutes to reach Earth. Because it is so far away, Neptune takes about 165 Earth years to complete one orbit around the sun. It was not discovered until 1846, making it the only planet found through mathematical prediction rather than direct observation: astronomers noticed irregularities in Uranus’s orbit and calculated where an unknown planet must be pulling on it.

Neptune is an ice giant — a planet composed primarily of water, ammonia, and methane ices surrounding a rocky core, all wrapped in a thick atmosphere of hydrogen, helium, and methane gas. It is about four times wider than Earth and has about 17 times Earth’s mass. The methane in Neptune’s atmosphere absorbs red light and reflects blue, giving the planet its vivid blue color. Despite being the outermost planet and receiving very little sunlight, Neptune radiates about 2.6 times more heat than it receives from the sun — suggesting it has a significant internal heat source left over from its formation.

Neptune has the strongest winds in the solar system, with gusts measured at up to 1,200 miles per hour — faster than the speed of sound on Earth. When Voyager 2 flew past Neptune in 1989 — the only spacecraft ever to visit the planet — it photographed a massive storm system in the southern hemisphere called the Great Dark Spot, comparable in size to Earth. Unlike Jupiter’s Great Red Spot, which has persisted for centuries, Neptune’s storms appear and disappear over years or decades. The Hubble Space Telescope has observed multiple dark spots appearing and fading since the Voyager flyby.

Neptune has 14 known moons. The largest, Triton, is one of the most unusual moons in the solar system. It orbits Neptune in the opposite direction of the planet’s rotation — called a retrograde orbit — which strongly suggests it was captured from the Kuiper Belt rather than forming in place. Triton has a surface of frozen nitrogen and geysers that shoot nitrogen gas several miles into its thin atmosphere. Because of tidal forces from Neptune, Triton’s orbit is slowly decaying; in about 3.6 billion years it will come close enough to be torn apart by Neptune’s gravity, likely forming a ring system as spectacular as Saturn’s.

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