1: Associated With All Things Fast
In Roman times Mercury was a very busy god of commerce, wealth, eloquence, messages, travelers, luck, trickery and thieves, whose other responsibilities included conveying the dead to the underworld. With so many duties and delegations it was necessary that he be remarkably fast and capable of flight, and his name has become associated with a great many things, such as a liquid metal which moves so fast it is sometimes called quicksilver. A line of cars used to be named after him, and in the DC comic books, the original Flash wore the same metal winged type helmet that Mercury is often seen wearing, after the superhero received his powers from the ancient Greek god himself. His name was also given to the fastest moving of the planets, our topic for today, Mercury!
2: How Fast?
And when I say fast, I mean fast. It orbits the entire Sun in just 88 days. The circumference of Mercury’s orbit is 35,983,125 miles (57,909,227 km). It travels at 105,946 mph (170,503 km/h) or 1766 miles (2842 km)/minute or 29.42 miles (47.36 km)/second.
3: Small But Hot
Mercury is our smallest planet, and the one closest to the Sun. It’s only the second hottest planet, though, as unlike the hottest plant Venus with its thick atmosphere, Mercury’s thin atmosphere is less able to trap in the heat. However, it is hot enough to have liquid lead on the surface on the Sun-side, but the night-side drops down to as little as 173°C/ 280°F.
4: Plenty of Frozen Water Deposits
You wouldn’t expect it on such a hot world, but there are permanently shadowed craters and basins at the North Pole that have plenty of water ice. This was revealed by only the second probe to visit this planet. Mariner 10 visited briefly in the mid-1970s, and now an on-going mission called Messenger is telling us more about this hard to visit planet. Could there be intermediate zones between the permanently frozen or boiled-dry state where liquid water and organics co-exist and life of some description might flourish?
5: One Day Twice As Long As Its Year
Mercury’s year may be 88 Earth-days long, but its day is 176 Earth-days long, or twice as long as its year. This is because Mercury is almost tidally locked to the Sun. We Earthlings only ever see one face of the Moon, because it is completely tidally locked to Earth. The Moon completes one revolution every time the Earth turns once on its axis. Mercury has a few more hundreds of thousands years before it becomes tidally locked.
Sitting near the bull’s-eye (the Sun) of a cosmic shooting gallery, Mercury is the most cratered planet in the system, with a surface littered with new impact craters found inside older ones. Unlike other planets whose craters are smoothed away by geological processes, Mercury’s main surface processes have not erased its craters and basins (250km+), which range in size from 100 metres to as big as 1300 km across.
7: Molten Core and Active Magnetosphere
Despite its small size, Mercury still has a molten core which surprised scientists. Such a small planet should have lost its heat and solidified, but Mercury’s core churns on, generating a magnetic field (albeit one hundredth that of Earth) and an actual magnetosphere around the planet to deflect the solar wind. Scientists suspect that the core may be composed of lighter metals or sulfur. BepiColombo, a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), will be headed to Mercury in July 2016. It will be investigating the anomalous magnetic field.
8: Hubble’s Limitations
People wonder if there are any Hubble Space Telescope images of the planet. The fact is that we’ll never get a look at Mercury with the HST because it is too close to the Sun, and the light from the Sun would destroy Hubble’s optics and associated electronics instantly. And it couldn’t compete with the terrific views we’re getting from the Messenger probe anyway.
9: Seeing Mercury
Interestingly, you can see Mercury with your own, unaided eyes. All you have to do is know where the sunrise occurs and have a clear view to the horizon. A few minutes before sunrise, Mercury makes its appearance and then vanishes as it is overwhelmed by the light of the rising Sun. At night you can watch the sunset, and after the Sun is gone and the twilight dissipates you can see Mercury as it disappears down below the horizon. The ancients, before any written history, knew about Mercury. The first written record found mentioned it so casually that it was evident that it was a well-known companion of the Sun for a very long time.
10: Most Eccentric Orbit
At closest approach (perihelion) Mercury is only 28,583,702 miles (46,001,009 km) from the Sun but at its greatest distance (aphelion) it is 43,382,549 miles (69,817,445 km). Its orbit precesses as it orbits the Sun, like it is drawing the petals of a flower. In fact its motion was so peculiar and hard to predict that it actually took Einstein’s general relativity calculations to figure it all out.
..One Last Thing
So that’s the story of our tiniest planet. It’s fast and slow (years and days); hot and cold at the same time; it’s naked-eye observable; its the closest to the Sun, but has water and who knows maybe even life. One other thing: It passes between us and the Sun about 13 or 14 times per century. The next time it will do so is May 9, 2016. Get or build yourself a solar scope (not a telescope –you’ll blind yourself) and have a look at the Sun sometime. Here’s what one fellow did.. have a peek