Recalling the elementary-school mnemonic My Very Educated Mother Just Served Us Nine Pickles, you would know that Mercury is the first and closest planet to the Sun. It is also the fastest-- completing a solar year in 88 Earth days. Mercury’s bright, brief apparition in twilight skies inspired its naming after the Greco-Roman herald of the gods. Though familiar to ancient stargazers, our modern scientific understanding of Mercury unveils a bizarre, paradoxical world.
Its Moon-like surface is toasty on the day side, up to 800 ? F. Yet Mercury is not the hottest planet-- Venus holds that infernal honor, roiling at nearly 900 ? F beneath a brutal greenhouse atmosphere. Mercury’s near-vacuum atmosphere traps no heat; thus, the night side is fantastically frigid, down to -276 ? F within deep polar craters. Here, water is frozen like rock in eternal shadow.
Mercury completes one solar day in 176 Earth days, or two Mercurian years. Its torpid rotation reinforces surface temperature extremes, as does Mercury’s highly elliptical orbit. At Mercury’s nearest solar distance (perihelion), sunlight intensity is 2.5x greater than at Mercury’s furthest distance (aphelion), when the night side is coldest.
Near perihelion, the Sun stands still in the Mercurian sky, as Mercury’s orbital and rotational speeds even out. Gradually, the Sun shifts eastward as orbital speed increases. Roughly four Earth days later, the Sun will shift westward, as rotational speed overtakes orbital. Depending on surface location, the Sun will slowly rise, then set, then rise again-- or the reverse at sunset. Or the Sun will lazily zig-zag near the zenith. At aphelion, the Sun will not stray far from the horizon.
Mercury is our closest planetary neighbor on average, but rather tricky to reach. Situated deep inside the Sun’s massive gravitation, Mercury is easy to overshoot, but backtracking is quite difficult. To date, three unmanned probes have made it. In 1974, NASA’s Mariner 10 executed three flybys, mapping half of the surface before exhausting its fuel in 1975, becoming a solar derelict. Thirty-six years later, NASA’s MESSENGER probe successfully entered Mercurian orbit, completing Mariner 10’s survey mapping before crash-landing in 2015. The European and Japanese space agencies jointly launched BepiColumbo in 2018, which has already executed several flybys. It will enter orbit next year to study Mercury’s geology, atmosphere, and magnetosphere.
Given the conditions, colonizing Mercury would be arduous and hazardous. Yet, an underground polar colony is hypothetically possible, where ambient thermal and radiation levels would be hospitable, and abundant water ice accessible. While unlikely, Mercury might harbor native life within mineral-rich ice reservoirs, as extremophilic microorganisms not unlike those found on Earth.
The messenger god was also a sly trickster, schooling others through riddles and wiles. His planetary namesake is no different— a peculiar realm of chiaroscuro contrasts, utterly unlike our terrestrial experience. Yet what might it reveal to intrepid future explorers? Only time will tell.
Music written and produced by Kenny Mihelich. Western Slope Skies is produced by the Black Canyon Astronomical Society and KVNF Community Radio. This feature was written and voiced by Michael T. Williams.