MESSENGER makes history at Mercury! Image: NASA

NASA’s MESSENGER spacecraft successfully achieved orbit around Mercury at about 9pm EDT on Thursday (Mar 18).  It’s been a long journey to one of the nearest planets. Launched August 3, 2004 the trip has been 4.9 BILLION miles (7.9 BILLION km)!! Hey it was fuel efficient though, the trip made use of the gravity assists of flybys to save fuel.

No, it’s never been done before.  You’d think it would have been long ago until you think about the technical challenges, heck just the temperature alone is huge, Mercury can reach over 441^o F (227^oC) on the dayside (hotter in spots) and -279^oF (-144^oC) on the nightside.

Mercury is a fun planet to ponder on, the sun is about nine times brighter than it is here.  There is almost no tilt to the planet so the poles are dark and extremely cold.  There has been radar signatures of ice at the poles, not sure if that was ever confirmed but at -234 degrees F if it was there, it still is.

Mercury does rotate slowly, about once every 58.7 days, and it has a year of about 88 days.  Since the rotation is exactly two thirds of its orbital period (year) a day on Mercury is 176 days long.  It’s called a 3:2 Spin-Orbit Resonance.

You’d also think the closest planet to the sun would have the most dead center orbit of all, being closest to the gravity source we orbit around, but no Mercury has an orbital inclination of 7 degrees the most of any planet.  This is different than the planet’s tilt, You can think of orbital inclination as the travel above and below the Sun’s equator.  Likewise you’d think Mercury would be the most circular of all,  but no, the orbit gets as close as 0.31 AU and as far as 0.47, this is known as the eccentricity and yes since Pluto is no longer a planet, I think that means Mercury is the most eccentric.

The Caloris Basin a crater 833 miles in diameter (1340 km) made as most craters are: a huge impact. In fact on the opposite side of the planet you can see where the seismic waves converged.  Maybe that’s why the iron core of Mercury is 75 percent of its radius and 60 percent of its mass.

Oh you can make Google Earth into Google Mercury with a KML file available at the the MESSENGER website.

It will be exciting to see the results of the MESSENGER mission as it unfolds as the science is set to start on April 4, 2011.