Mercury The First Planet
Mercury is the first planet and I would say the planet that is most often ignored. Is this because it looks like the Moon? Are we only interested in planets with atmospheres (like Venus or Saturn) rather than rocky objects littered with hundreds of thousands of craters? Take a look at the picture above. This photo of Mercury was taken by Nasa’s Mariner 10 spacecraft in 1974.
Mariner 10 took this image while it was slightly behind the lighted hemisphere of Mercury from about 3.3 million miles away. Now take a look at the image to the right. This image was taken of our own Moon. Doesn’t it look like the picture of Mercury? They both have smooth plains and are heavily cratered. Why would we want to look at Mercury when we have the same thing right next door?
Seriously, while it is true that Mercury hasn’t been explored as much as other planets in our solar system, it’s not because it looks just like the Moon. There are other more practical reasons why. Sending probes to Mercury is very difficult because Mercury is so close to the Sun. The closer you get to the Sun, the higher it’s gravitational attraction. A spacecraft will accelerate as it nears the sun. To enter orbit around Mercury would require the spacecraft to decelerate. Since Mercury has no atmosphere, deceleration would have to be accomplished using rocket motors which would require enormous amounts of fuel or complicated gravitational maneuvers which would take a long time.
Only two space probes have ever visited Mercury. As mentioned earlier, Mariner 10 flew by the planet in 1974. The Messenger probe was launched on August 3, 2004 and made it’s first contact with Mercury in 2008. Since then it has made two fly-bys and Nasa hopes to insert the spacecraft into an elliptical orbit around it in March of 2011 – just a couple of months from now!
We’ll post more news about the Messenger Mission as we get it.