Mercury as seen by the MESSENGER robotic spacecraft (photo from http://www.solarsystem.nasa.gov)
Mercury is the smallest planet in our solar system (a little larger than our moon) and the closest to the sun, being only 36 million miles away. In contrast, Earth is 93 million miles away from the Sun. Mercury “flies” around the sun at an average velocity of approximately 30 miles per second. Thus, a “year” for Mercury is only 88 days (The Planets by Dava Sobel; 2006). In contrast, a “day” on Mercury – the time it take the planet to rotate once – is 59 Earth days long (that’s 1,416 hours!). Thus, as Dava Sobel put it, “…the years hurry by, while the days drag on forever.” In HPL’s day the rotation of Mercury was unknown but it was hypothesized that it was very slow or did not rotate at all.
HPL noted that the existence of an atmosphere on Mercury was generally disputed. However, the MESSENGER mission revealed that Mercury has a thin atmosphere (called an exosphere) that is composed mostly of oxygen, sodium, hydrogen, helium and potassium. HPL did correctly note that Mercury has no satellites.
MESSENGER probe (www.nasa.gov)
While Venus has the highest temperatures in the solar system due to its thick atmosphere trapping all heat and Pluto has the lowest due to its distance from the sun, Mercury has the largest variation in temperature on any single planet or dwarf planet due to its slow rotation (Dava Sobel, 2006). Daytime temperatures can reach 800 degrees Fahrenheit (430 degrees Celsius) and nighttime temperatures drop to -290 degrees Fahrenheit (-180 degrees Celsius)(NASA). While the rotation of Mercury was not known during HPL’s time he did, based on the astronomical data of the time, hypothesize that Mercury must have one side eternally day and the other internally night (Collected Essays, Volume 3: Science). In turn, HPL thought that the range in temperature on Mercury at the time must be extremely large and the potential for life on that world was very unlikely.
As identified numerous times in his articles on astronomy, the best times to see Mercury is in the early evening hours in the spring or the early morning hours in the fall. Originally, the ancients thought this planet was two distinct celestial bodies; the “morning star” was named Apollo while the “evening star” was named Mercury. HPL also identified the difficulty in finding this planet in the heavens and noted that Copernicus was never able in his life to observe it (Collected Essays, Volume 3: Science).
A view of Mercury, Venus and the moon immediately after sunset on 10 June 2013 (www.astrobob.areavoices.com)
While HPL believed that it was very unlikely that life existed on Mercury, this did not stop him from incorporating Mercury as a “habitable” world in his stories. Specifically, in The Shadow Out of Time it was mentioned that in our distant future, after human civilization, the Yithians would transfer their minds from the Cone-Shaped Beings and into an advanced race of beetles. Later, after the eventual destruction of Earth the minds would then again migrate through time and space into the bodies of the bulbous vegetable entities of Mercury. Since the Yithians would travel both time and space, it is not known if the vegetable entities lives in our distant past or distant future. Besides their existence, nothing is known about the bulbous vegetable entities of Mercury, at least within the writing of HPL.
The Bulbous Vegetable Entities of Mercury (by Michael Bukowski on http://www.yog-blogspot.com)
Beyond the existence of the bulbous vegetable entities and his astronomical observations, HPL did not have a lot to say about Mercury. However, he did occasionally mention another planet that may exist between Mercury and the sun – the planet “Vulcan.” We will talk about this planet in the next article. Thank you – Fred.