Mercury as you probably know is the closest planet to the sun. It is approximately 35m miles (57m km) from the sun. That’s 2/3 closer than we are on Earth. When I say approximately, it is because it’s orbit is “eccentric” At it’s closest, it is 46m km and at it’s furthest, it is 70m km. (I will leave it up to you to convert to miles).
Why the difference? Up to the beginning of the 20th century, it was a huge dilemma among scientists. Many thought there must be another planet closer to the sun that we could not see. They even named it (Vulcan).
The truth was even more dramatic. There is no other planet. And when measurements were made with more accurate instruments in the 1920s, it became one of the first proofs of Professor Einstein’s * “General Theory of Relativity”. Don’t confuse this with his early (and more famous) “Special Theory of Relativity” - you know
e=mc².OK, I’m totally off my subject, as usual. So back to Mercury.
Guess what, it’s really hot there. Well, at least on one side. We used to think that it always faced the sun with one side like the same side of the moon faces us. After visiting Mercury with two spacecraft, we now know that Mercury does rotate, like something on a spit, very slowly. It turns out that Mercury rotates 3 times in two of it’s years. It’s as if our days each lasted four months. On a cold day, it gets to -300° F and on a warm day, a balmy 800° F.
A year on Mercury is about 88 days.
Mercury is often hard to see and was considered too close to the sun and too much of a hazard to point the Hubble Space Telescope at it.
The first spacecraft to visit Mercury was Mariner 10, which mapped only 45% of the planet. That was 40 years ago and scientists are still working with the Mariner information. Now, another spacecraft is on it’s way into orbit there. Messenger was launched in 2004, has already flown by Mercury and Venus once, and will finally settle into an orbit in 2011. Visit the Messenger website to follow the mission. Or if you are a student graduating, consider getting involved. Messenger is operated by the John’s Hopkins University in Baltimore, Md and by the Jet Propulsion Lab (who put up with me).
Have a look at some more pictures of Mercury.
If you want to know more technical information on our inner-most planet, go here.
* You probably didn’t know this but Professor Einstein and I are related. We have the same hair.