In our tour of the solar system, we should begin by exploring the innermost planet. A brief distance from the inferno of our sun we find it, hurtling through space at 40 to 60 km per second in its 88 day cycle around the sun. As we approach it we notice its similarity to your body much closer to Earth, our own moon. It too is heavily cratered, with no atmosphere (or only a trace of one) to protect its surface or erode signs of previous collisions. The sun as seen from this distance is approximately twice as large as from Earth, and we know this will be the most dominant force affecting our trip to this planet.
Now we’ve touched down and we take a fast look around. We know that the surface gravity of Mercury is 38% of Earth’s, so if we weighed 200 pounds before, here we weigh only 76 lbs. Looking up at the sky we see a black, star-speckled skies dominated by the fiery globe of sunlight almost 3 times bigger than we are knowledgeable about. There is only the faintest hint of an air, and the only way we even know it is there’s the instrumentation we have with us. It will be completely useless to us. The sun beats down unabated in all its fury, and the temperature hovers around 800 degrees Fahrenheit. If we had been on the night side the temperature would drop to -270 degrees. We would never live here without space suits.
Bending down to inspect the surface we find a layer of dust similar to what astronauts found on the moon. This is the result of centuries of meteor impacts, as well as the extreme temperature differentials implemented from a hellishly close sun. The processes which shaped this world across the eons were substantially different than those which shaped our home world.
Around us are the pockmarks of craters, some mountain ranges, and a horizon much nearer than that which we know at home.
Contrary to what astronomers once thought, there’s actually a cycle of days here, but it’s much different than anything we are accustomed to. Mercury is not tidally locked with sunlight, but tidal forces have slowed it to the point where its day is 58 of our times (really it will one day many years from now become locked one facet to its enormous neighbor). This means that Mercury’s day is about three quarters as long as its year. This results in some very peculiar observations if we were to stay that long. In certain places on this world we would then see the sun slow and really backtrack a brief distance before continuing its slow march across the sky.
We take one more look around the globe. No, Mercury is not an enticing place for people to go to. Maybe one day we will have reason to be here, either for the rich deposits of iron and other metals or for observational purposes, but this isn’t the day.
Mercury has been know and observed at least since the days of the Sumerians from the 3rd century BC. After the Sumerians there’s better documentation in the Babylonian Empire. Records from the 7th century BC refer back to much earlier documents which described observations of the planet. The Babylonians called the planet Nebu, after the messenger of the gods in their mythology. This is an interesting parallel to the Greek mythology and reference to the innermost planet. The ancient Greeks had two names for the entire world, Apollo visible in the morning and Hermes observable in the evening. They eventually came to understand that these were exactly the identical object, and it was even proposed this early in history that Mercury and Venus orbited the sun.
Early modern astronomy started making observations of Mercury in the early 17th century when Galileo turned an early telescope to the inner world. A sketchy vision of the planet developed from there, but its proximity to the sun has always made this one of the most difficult members of our solar system to study. It has only been recently with the advent of new imaging techniques that ground-based monitoring has drastically improved.
And what of research with space probes? This is also laced with technical difficulties. An application of Newton’s Laws of Motion shows that it requires more rocket fuel to achieve an orbit around Mercury than necessary to escape the solar system. Because of this just one spacecraft has visited the planet thus far, the Mariner 10. After its analysis of Venus, the probe made three flybys of Mercury in 1974 and 1975 as it mapped about 45% of the world’s surface. Its closest approach was 203 miles on March 16,1975. The Mariner 10 circles the sun in its own lone orbit around the sun to this day, although its digital instruments have long since been destroyed by the sun’s intense radiation.
Our toughest Mercury research project to date was started August 3,2004 with the launch of the Messenger by NASA from Cape Canaveral. After two quick flybys of Venus in 2006 and 2007 the Messenger will eventually work its way inward and make three flybys of Mercury in 2008 and 2009. It is carrying high resolution imaging devices, spectrometers to determine the composition of the crust, and magnetometers to study charged particles around the planet.
There is an astronomical event which is of interest to amateurs and professionals alike, but not always for any scientific value. After every couple of centuries there’s an occultation of Mercury and Venus. This occurs when Venus really passes directly in front of Mercury for a few minutes. The last one occurred on May 28,1737 and another will occur in 2133.
Much of Mercury’s mass is composed of an iron rich core. Recent theories suggest that this core comprises most of the 4879 mile diameter of Earth. Because of Mercury’s slow rotation period, there’s very little tectonic or volcanic activity.
There have been several theories introduced to explain why Mercury is so metal rich, and why its core features such a huge part of the world’s structure. One popular theory is that the world was struck by a large body early in its history and dropped most of its outer,”lighter”, mantle. Another theory is that the extreme heat of the early sun vaporized the outer part of the planet, giving the young Mercury a dense atmosphere of gaseous stone, which was carried away by the huge solar winds of a much more volatile sun. The competing theories to explain the unusually heavy makeup of Mercury will be analyzed by the approaching Messenger mission.
The Future of Mercury and Its Possible Role in Our Own Future
Mercury’s most dominant feature makes it an attractive part of our future: its huge stores of heavy metals, especially iron. Though its proximity to the sun makes it tough to envision humans working and living there, I could envision automated factories mining its own surface and freighters picking up the ore to bring it back for our use.
Mercury will remain pretty much as it is for centuries to come. As the sun slowly gains in intensity over the next 4 to 5 billion years, the planet’s surface temperature will slowly rise with it. Then a singular moment will arrive as the entire solar system changes with the beginning of the sun’s passing into its next stage. After the sun consumes a vital amount of its hydrogen gas it will, within a matter of only a couple days, enter its red giant stage.
At the point Mercury will be the first of the inner planets to be entirely consumed.