The 8 Planets Series: The Finale

For the last few months, if you stayed tuned to my “8 Planets” series, I updated information on each of the planets and major moons, taking you on a journey through the solar system. From Mercury to Neptune, the solar system holds many wonders, twists and turns, and bizarre objects. Coincidentally, the 8 posts, corresponding to each of the planets, was spaced out on the calendar roughly relative to the distances between the planets. The four terrestrial planets, Mercury, Venus, Earth, and Mars, are relatively close to one another (less than 1 AU). These four posts were published around the same time. However, for the gaseous planets, Jupiter, Saturn, Uranus, and Neptune, posts were spread out across months to correlate with these planets’ large distances from one another. Well, thank you for tuning in! To celebrate the “8 Planets” series I created a solar system mobile, as shown below. Enjoy! The next series will be “Astronomy and Mythology: The Naming of Celestial Objects.”

The 8 Planets – Part 8: Neptune




The last planet Neptune, is quite a spectacle, essentially a blue marble. As with Uranus, methane (trace amount) gives Neptune its blue coloration. Named after the Roman god of the seas Neptune was noted by Galileo in 1612, but discovered as a planet by Urbain Le Vernier, John Couch Adams and Johann Galle on September 23, 1846. Neptune has a very elliptical orbit, and was further than Pluto between 1979 and 1999. Uranus and Neptune are usually paired together as “ice giants.” Uranus is light blue, named after the god of the sky, while Neptune is dark blue, named after the god of the seas. Unlike Uranus’s bland surfaces, Neptune’s ephemeral storms make up the planet’s active atmosphere. The Great Dark Spot is comparable to Jupiter’s Great Red Spot, but the Great Dark Spot comes and goes. With the strongest gales in the solar system, winds (rotates opposite of the planet’s rotation direction) on Neptune have speeds up to 2,100 kph— almost reaching supersonic flow! Winds called the scooter that speed across Neptune reach up to 3000 kph! Although Neptune’s atmosphere is one of the coldest places of the solar system, Neptune has a faint, fragmented ring system called arcs discovered during the 1960s and confirmed during the 1989. The rings give off a faint red hue, comprising mainly of ice and carbon-based materials. Like that of Uranus, Neptune’s magnetosphere is also relatively tilted (47º). The pressure on Neptune is so great that it rains diamonds there! On Neptune, that pole facing the Sun is 10ºC hotter than the other pole, so when the seasons change, frozen methane warm up and leak out into space.


Triton and Nereid

Triton and Nereid

Neptune has 13 known moons, the largest are Triton and Nereid. In mythology, Triton and Nereid are Neptune’s sons. Interestingly, Triton has a retrograde orbit (spins east to west), which suggests the Neptune gravitationally pulled Triton into its orbit. In fact, in 3.6 million years, Neptune will pull Triton past the Roche Limit (past this limit, all moons are doomed to crash into the planet), and the moon will crash into Neptune! Neptune’s second largest natural satellite, Nereid, an irregular moon, has one of the most eccentric (elliptical) orbits in the solar system.

MISSIONS: Voyager 2


  • Order in Solar System: #8
  • Number of Moons: 13
  • Orbital Period: 164.8 years
  • Rotational Period: 16.11 hours
  • Mass: 1.0243 x 10^26 kg ( 17.147 Earths)
  • Volume: 6.254 x 10 ^13 km³ (57.74 Earths)
  • Radius: 24,764 km (3.883 Earths)
  • Surface Area: 7.6183 x 10^9 km² (14.98 Earths)
  • Density: 1.638 g/cm³
  • Eccentricity of Orbit: 0.0112
  • Surface Temperature (Average): 72 K
  • Escape Velocity: 23.5 km/s
  • Apparent Magnitude: 8.02 to 7.78

The Solar System: Basics

The Solar System


  • Eccentricity of Orbit: measures the ellipticity of orbit (ranges 0-1, with 0 as spherical and 1 as very elliptical)
  • Density: mass per unit volume; mass in grams and volume in cubic centimeters
  • Oblateness: measures how much the middle section of the planet bulges
  • Surface Gravity: the larger the surface gravity, the thicker the atmosphere as gravity pulls in more gases
  • Albedo: measures the fraction of light reflected compared to the amount of light received from the Sun; the higher the albedo, the more reflective the surface
  • Escape Velocity: minimum speed or velocity needed to escape the planet’s gravitational pull
  • Rotation: most planets rotate in counter-clockwise direction (prograde); others rotate in the clockwise direction (retrograde)
    • Rotational period is shortest for gaseous planets and longest for Venus
  • Roche Limit: about two and a half times the radius of the planet; within the Roche Limit, matter cannot accretes to form moons because the tidal force of the planet tears matter apart to form rings

Giant Planets: Giant planets have lighter elements such as hydrogen and helium in their atmospheres. They have stronger gravity and are at larger distances from the Sun. Jupiter, Saturn, and Neptune are stormy with great spots of lasting storms and belts and zones. However, Uranus is comparatively bland and uniform. All giant planets are home to convection, or hot gases rising and cold gases falling.

Terrestrial Planets: Terrestrial planets have heavier elements such as carbon, oxygen, and nitrogen. Mercury is most heavily cratered while Earth is least cratered. Larger terrestrial planets have plate tectonics. Earth has a sizable magnetic fields that can protect it from solar wind particles and Van Allen Belts. Earth has the “Goldilocks phenomenon,” or the right conditions for the development of life.