Nothing But the Facts About Neptune

 1) Position in the solar system: 8th planet from the sun

2) Closest distance to the sun: Perihelion: 4.444x10^9 km

3) Furthest distance from the sun: Aphelion: 4.546x10^9 km

4) Minimum distance to Earth: 4.292x10^9 km

5) Neptunian day: 16.11 hr

6) Neptunian year: 164.8 Earth years

7) Axis tilt: 28.32°

8) Orbital inclination to ecliptic: 1.77°

9) Orbital eccentricity: 0.0086

10) Diameter (equatorial): 49,528 km

11) Mass: 1.024x10^26 kg, approx. 17.1 times that of Earth

12) Gravity: 1.14 (Earth = 1)

13) Escape velocity: 23.5 km/s

14) Temperature: -201°C at 1.0 bar pressure

15) Mean surface pressure: >1000 bars

16) Atmospheric composition: 80% hydrogen, 19% helium, 1.5% methane (numbers do not add up to 100% due to uncertainty) with trace amounts of hydrogen deuteride ("heavy" hydrogen) and ethane, and aerosolized crystals of ammonia ice, water ice, ammonia hydrosulfide, and methane ice

17) Number of moons: 13

18) Ringed system? Yes

19) Magnetic Field? Yes

1) Discovery as a triumph of scientific prediction: Neptune was predicted to exist by John Couch Adams and Urbain Leverrier, based on features observed in the orbit of the planet Uranus. The hypothesis explained these features as gravitational effects of an eighth planet. Johann Gottfried Galle discovered Neptune when he observed it in the predicted location on September 23, 1846.

2) Nearly discovered by Galileo: Galileo observed Neptune in the 17th century through his telescope, but by coincidence he observed it just as it was beginning its retrograde motion. For that reason, he did not recognize its planetary movement and thought it was a fixed star.

3) Extreme weather: Unlike its relatively calm neighbor, Uranus, Neptune has extreme weather. A storm called the Great Dark Spot measures 13,000 km long, about the diameter of Earth. Windspeeds on Neptune reach the near-supersonic speed of nearly 600 km/s, despite the fact that the planet receives 1/900 as much energy from the Sun as Earth.

Sample Neptune Fact Sheet (NASA): http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html

JPL Photojournal: http://photojournal.jpl.nasa.gov/catalog/PIA02245

Science Magazine: http://www.sciencemag.org/cgi/content/abstract/251/4996/929

Neptune true color image: http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=2424

Neptune and Triton image: http://www.nasa.gov/worldbook/neptune_worldbook.html

Clouds of Neptune image: http://voyager.jpl.nasa.gov/science/neptune_magnetic.html.

Neptune. (Supplied by NASA)