• Neptune is the fourth largest planet in the Solar System, and is the most distant official planet that orbits the Sun. It is considered one of the "gas giants" because it is composed mainly of gases, and lacks a solid, rocky crust like Earth.

• 1. Discovered on September 23, 1846
  2. Discovered by three scientists: Urbain Le Verrier, John Couch Adams and Johann Galle
  3. Named after the Roman god of the ocean.
  4. Radius: 24,764 kilometers (3.8 times Earth's radius)
  5. Circumference: 155,597 kilometers
  6. Surface area: 7.64 million square kilometers (14.9 times Earth's)
  7. Mass: 1.02x10²⁶ kilograms (17.1 times Earth's)
  8. Average distance from the Sun: 4.49 billion kilometers
  9. 13 known moons in its orbitNASA-JPL: Neptune - Facts & Figures
  10. 1. Hydrogen
      : 80.0%
  11. 1. Helium
      : 19.0%
  12. 1. Methane
      : 1.5%
  13. 1. Trace amounts of Hydrogen Deuteride, EthaneNASA: Neptune Fact Sheet

• Astronomical Surprise

  Neptune's existence was mathematically-predicted by Galileo between 1612 and 1613—more than two hundred years before it was visually confirmed. However, Galileo believed that the object accounted for in his calculations was a fixed star. Astronomers didn't discover that Neptune was in fact a planet until 1846.NASA-JPL: Neptune - Overview

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