The planet Neptune as captured by Voyager 2 in 1989 (solarsystem.nasa.gov).
Neptune is the outermost planet of our solar system and is one of the two ice giants (the other being Uranus). It is 2.8 billion miles or 30.07 A.U. away from the sun. It takes Neptune 165 Earth years to make a complete orbit around the sun and a “day” on Neptune is approximately 16 hours (solarsystem.nasa.gov).
HPL called the discovery of Neptune “…one of the most remarkable achievements of astronomical science, being no mere accident, but the result of long and extremely precise calculation” (Collected Essays: Science, Volume 3 by S.T. Joshi, 2005) and he was correct. Before the planet was actually discovered, its existence was theoretically predicted by “reverse calculating” the irregulatrities in the motion of Uranus. Even when John Couch Adams took Saturn’s gravitational pull into consideration, it could not account for the movement of Uranus. Something else had to be contributing to the observed conditions. By mid-September 1845 Adams final solution was completed for the orbit of Uranus and it required the existence of an another planet, a planet beyond Uranus. Adams did not know it at the time, but the position he predicted for this unknown planet was within 2 degrees (Planets Beyond: Discovering the Outer Solar System by Mark Littmann; 1990). This unknown planet turned out to be Neptune.
John Couch Adams (Wikipedia.org)
A Frenchman, Urbain Le Verrier, also worked out the same solution as Adams at about the same time. The astronomer Johann Gottfried Galle used both of their calculations to correctly locate Neptune. There was a bitter dispute between England and France on who should be credited for finding Neptune. Eventually, it was decided both astronomers should share the credit. For HPL’s part, he cites both of astronomers in the discovery of Neptune in his Science Essays. Again, the most incredible thing about the discovery of Neptune was that it was theoretically discovered through mathematical calculations before it was actually observed in the sky. Based on his quote provided above, this impressed HPL and provided additional support on the value and power of the scientific method.
Urbain Le Verrier (Wikipedia.org)
Similar to Uranus, in HPL’s day little was known about Neptune. In the early 20th century, Neptune was known to have a greenish colour and one moon. HPL hypothesized that it was probably hot with a “small density” like many of the other outer planets (Collected Essays: Science, Volume 3 by S.T. Joshi, 2005). Again, remember in HPL’s day all of the outer planets were thought to be semi-molten, which would be attributed to volcanic activities and/or the failure of developing into a sun (e.g. Jupiter).
Thanks to the Voyager 2 mission we know a lot more about Neptune than we did in HPL’s time. Similar to Uranus, Neptune is an ice giant, composed of a hot, dense fluid of “icy” materials, including water, methane and ammonia, probably above a solid core approximately the size of the Earth (solarsystem.nasa.gov).
In HPL’s time Triton was the only moon identified for Neptune. However, currently, Neptune has 13 confirmed moons and 1 waiting official confirmation. Neptune has 6 confirmed rings, a Great Dark Spot, a Little Dark Spot, smaller cloud features and dark bands.
The surface of Triton – one of the moons of Neptune; photographed by Voyager 2 in 1989 (solarsystem.nasa.gov)
Finally, it should be noted that Triton is only one of two satellites in our solar system that are known to possess a permanent atmosphere – the other being Saturn’s moon Titan. More than likely Triton’s atmosphere is thin and originates from the vaporization of methane ice. However, Triton also possesses molecular nitrogen. There are a few organisms on Earth, such as some blue-green algae, that have the ability to “fix” molecular nitrogen from the atmosphere as an energy source. Are there similar microbes on Triton, taking advantage of its atmospheric nitrogen?
The blue-green alga (also known as cyanobacteria) Anabaena. The clear cell in the upper right corner is called a heterocyst and is a specialized cell used to fix atmospheric nitrogen for energy. Are there microbes on Neptune’s moon Triton that use a similar biochemical pathway? (photo-micrograph from PhycoTech).
Next time we will talk about how HPL incorporated Neptune into his stories. Thank you – Fred.