II: (Sometimes) Hotter than Hell: Welcome to Mercury
Even the least informed among you will be aware that Mercury is the closest planet to the Sun, and therefore the hottest. Well not quite. I always thought this, but it seems that because Mercury has no atmosphere, and therefore no way to retain heat, despite its heat source being only 58 million km away, its surface temperature fluctuates wildly between day and night. In the day it can reach temperatures of up to 800 degrees Centigrade, whereas at night it plunges to -173 C. Anyone trying to list off the planets (come on, who would fail at such a task? Oh well, I remember someone on a quiz recently apparently forgetting the soil he stood on was part of a planet, and thinking it was Mercury, Venus, Mars….) will always know that Mercury comes first, so it’s always uppermost in people’s minds. It’s also the smallest of the planets as you might expect, a mere 0.05 times the size of Earth, with gravity at 0.3, which I guess means you could fly on Mercury, if you weren’t busy being fried to a crisp, that is.
Mercury is one of only two planets in our solar system devoid of moons, its nearest neighbour being the other. In some ways, Mercury displays some of the characteristics of our moon at least - pock-marked with craters, inactive, dead and without any atmosphere, although nobody to my knowledge has ever written a song called “By the Light of the Silvery Mercury” or suchlike. Just doesn’t have the same romanticism. Another reason why, perhaps, Mercury doesn’t figure all that much in human culture - certainly not as much as Mars, Saturn, Jupiter and Venus, for instance - is that it’s very damned hard to see. Because its orbit is within that of Earth, and due to its proximity to the Sun, it can usually only be seen after sunset on the western horizon and before sunrise on the eastern.
It’s a lot denser than Earth, by which I don’t mean it gets a lower SAT score: its core takes up about 55% of the planet, whereas ours only extends to 17%, and Mercury is one of the richest sources of iron in the solar system. Long narrow ridges extend for several hundred kilometres along its surface, as well as mare*-like plains and craters, similar to those on the moon. Like the moon, it also has highlands, mountains, valleys and escarpments. Some of the craters are hundreds of kilometres wide, though some are quite small. The largest is called
Caloris Basin or
Plantitia, and is 1,500 km wide.
Due to the contraction which occurred as Mercury cooled, the surface has been deformed into things like wrinkle ridges and lobate scarps (curved or scalloped cliffs), as well as compression folds known as
rupes or cliffs. The many volcanoes on the planet (billions of years dormant now of course) are all of the shield variety, which means they’re almost flat to the ground, rather than the ones we’re familiar with, caldera and mountains. Perhaps strangely, given its proximity to the Sun, it’s theorised that ice may exist on Mercury. This is supported by the fact that the temperature at the poles, which never receive direct sunlight, is always at about -170 C, and cold traps have developed on the floors of deep craters at the poles.
Messenger, a probe sent out in 2012, confirmed that there is enough water ice at the north pole of Mercury to “encase all of Washington DC in a block of ice two and a half miles deep”. The next probe to visit Mercury, scheduled to arrive in 2025, will explore this further.
* A Mare is a flat, basaltic plain created by volcanic eruptions, the word coming from the old Latin for sea, which is probably how they were once viewed in early times.
Ever asked yourself if this day would ever end? Well thank your lucky stars you aren’t on Mercury, where the day lasts 1,400 hours or approximately 58 Earth days! Try getting through
that one without telling the boss where to shove his job! As for years, well this is quite weird, because it seems Mercury spins faster on its axis than it rotates around the sun - a trip which takes it 87 days - meaning that one Mercury year doesn’t even last two Mercury days! Imagine all the presents you’d be getting for birthdays! Then again, imagine how quickly you’d age if every year was only 87 instead of 365 days. Oh man! I’d be, what, well over two hundred years old! Bet I don’t look a day over a hundred though.
Because the planet’s tilt is almost zero, the least of any of the planets in our system, an observer on Mercury would see the sun rise almost two-thirds of the way over the horizon, then reverse and go back down and come back up, all in the same day! Hey darling, let’s go watch the sun rise, set and rise again, shall we? It’s so romantic! Oh but that’s not the best of it. Once every Mercurian year (every other Mercurian day, in other words) at certain points on the planet’s surface the sun goes overhead, reverses direction, comes back over again, reverses direction again and comes back over a third time. At this point, the Sun is basically stationery. No, that’s not right is it? That would mean our native star suddenly became a load of pens and paper clips and notepads. Stationary, that’s the one. Not moving. Stopped. Like the queue in the post office just when you
have to catch that bus.
Kind of amazing to hear that a report issued in March 2020 suggested that life may at one time have existed on Mercury, although it’s unlikely to have been bronze-suited Mercurians saluting the huge god that seemed always to be watching over them, but rather tiny micro-orgasms, sorry organisms. Not expecting too much in the way of written history, then. Interesting that several cultures all linked the planet with their version of the messenger of the gods, the Babylonians naming it Nabu, the Greeks Hermes and the Romans of course Mercury, which was the one which stuck. This might be because
(Trollheart Hypothesis # 340, all rights reserved) it is the planet closest to the sun, which was generally seen as the father or creator god, so this planet would be designated as its messenger. Maybe. Who knows?
Probes sent
Mariner 10
Launched: 1973
Reached Destination: 1974
Results: Mapped about 45% of the planet, confirmed its very weak atmosphere of helium, the existence of a magnetic field and also confirmed the highest deposits of iron found in any of the planets. Determined maximum and minimum temperatures on the surface of the planet.
Photographs taken: 2,800
Mission ended: 1975
Termination of probe: Deactivated remotely and believed yet to orbit the Sun
MESSENGER (MErcury Surface Space ENvironment GEochemistry and Ranging)
Note: Isn’t it weird how everything associated with Mercury turns out to have to do with messengers? Obviously, this one was planned, but still. I mean, let’s be honest, the acronym is about as forced as you can get. It could easily have been called the Monsignor, or I don’t know, the Massager?)
Launched: 2004
Reached Destination: 2008 (but flybys only; entered Mercury orbit 2011)
Results: Mapped 100% of surface, examined the atmosphere, made detailed study of the planet’s geology from orbit, studied its magnetic field, its surface, the poles and the core. Discovered the presence of water, also volcanoes. The revelation that there were carbon-containing organic compounds on the planet led to speculation that life might have existed there once.
Photographs taken: 100,000
Mission ended: 2015
Termination of probe: Crashed into Mercury
Future probes
BepiColumbo
Launched: 2018
To reach Mercury: 2025
Mercury-P (Меркурий-П)
Launch date: 2031 (planned)
As you might have gathered from the characters, this is being launched, or at least its launch is proposed, by the Russian Space Agency, and if successful will be the first probe to actually land on the surface of Mercury.