Robert’s Out of This World Space Odyssey: Mercury, the Littlest Planet

Let the exploration of the Milky Way Galaxy commence! I posted about stars a few weeks ago, so now let’s talk about the planets! I heart all of the planets equally so we'll just talk about them in order, starting with Mercury...

Mercury is the small planet right next to the sun. It is the smallest planet in our solar system (about the size of Earth’s moon), but is the second (to Earth) most dense planet. Being dense basically means it is really heavy for its size (science people are cringing at this definition, but it works, so back off!). Mercury is the closest planet the sun. At its closest it is only 28,580,000 miles (46,000,000 kilometers) away from the sun’s surface. Being so close to the sun means daytime temperatures on the surface of this tiny planet reach a sweltering 430°C (800°F). Mercury does not have an atmosphere (atmospheres are like a big blanket - they can hold in warmth and keep out space trash) so a night on Mercury usually plummets to around -180°C (-290°F). Imagine dressing to go out for dinner.

Mercury is named after the Ancient Roman god, Mercury. Mercury (the god) was the FedEx god who could get places the fastest with his super-fly winged shoes. The name is fitting since the planet Mercury orbits the sun faster than any other planet. One year (a full rotation around the sun) takes Mercury 88 Earth days. A day on Mercury (one full rotation around the axis – an imaginary line running through the center of the planet) is 59 Earth days long. Since it is going around the sun so quickly, but rotating so slowly, it takes 176 Earth days to have 1 solar day (to go from sunrise to sunset). Isn’t that kind of bizarre?

Being so small and close to the sun makes seeing Mercury a little difficult. Thirteen times a century, Mercury will pass in front of the sun and people on Earth will be able to see the planet (this is called a transit). The next time we can do this is May 9, 2016.

In 1974-1975 the US space probe, Mariner 10, did flybys of Mercury and provided people on Earth with the first up close images of the planet. Basically, it looks like our moon – it’s full of craters and mountains created by comet and meteor impacts. Radar imaging done in 1991 shows that despite being so hot, the poles (which stay cold) may contain frozen water. NASA has the Messenger probe aimed at Mercury now. The probe did flyby pictures in 2008 and 2009. Messenger will settle into orbit around Mercury in 2011 and study the planet’s composition and magnetic field for a year.