Messengers look at Mercury. Click for larger. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

As the Messenger spacecraft approached Mercury for its third and final flyby, it took this image of the planet.  Taken through red, green and blue filters we can see Mercury in full color.  I am a little surprised at how much color there is actually, I had expected a rather bland grey tone with the occasional bright crater.

Mercury is a pretty remarkable planet.  It’s a pretty bright place too.  Apparent brightness is inversely proportional to the square of the distance, so if Mercury is 3 times closer to the Sun, the Sun appears 3² or 9 times brighter than it does to us on Earth.

You would think that being so close to the Sun the orbit of Mercury would have a pretty circular orbit, it doesn’t, it has the most elliptical orbit of ANY of the planets!

Of course you know it’s hot, as hot or hotter than the oven in your kitchen, but you knew that. A long hot day on Mercury is really long too, 176 days long actually.   As hot as it is, the nights are bone chilling to say the least, how about -279 ^oF!  At one time there was speculation there may be ice in some of the craters in the perma-shade at the poles – sound familiar?  I”m not sure what the current thinking is on that.

Mercury is very dense, 5.43 grams/cc, almost as dense as Earth at 5.52 grams/cc.  How come?  Mercury has a HUGE iron core, the iron core is about 75 percent of the radius of Mercury. Messenger has found that iron is also prevalent in the mantle.  This was kind of an unexpected finding, the conventional thinking was the mantle was mostly basalts like the moon.

How the iron core came to be is for another time.

Head over to the Messenger site for much more on Mercury.