Mercury’s Swift MESSENGER

Exploring a Hot/Cold Little World

This WAC image showing a never-before-imaged area of Mercury’s surface was taken from an altitude of ~450 km (280 miles) above the planet during the spacecraft’s first orbit with the camera in operation. The area is covered in secondary craters made by an impact outside of the field of view. Some of the secondary craters are oriented in chain-like formations. Courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

Yesterday was a banner day for the folks who run the MESSENGER mission to Mercury.  The first images that the spacecraft has taken since it achieved orbit around the planet began streaming back to Earth.  Now, there have been a good many flyby images of Mercury, not all of them high-res, since we began exploring the solar system in the mid-1960s with spacecraft. But, these are the first taken from a spacecraft orbiting the planet.  This means that we’re going to (finally) get to see every bit of this world’s ancient, cracked and cratered surface.

The first images (which you can browse at the MESSENGER Web Site) are pretty detailed.  For example, this Wide Angle Camera view shows an area near the north pole of the planet.  It was taken as the spacecraft made its closest approach to the sunlit side of the surface.  The long shadows are caused because the Sun is at an oblique angle to the spacecraft, which was just about to cross over into darkness.

The polar region of the planet is of great interest to astronomers because some radar studies of the area taken from Earth seem to imply that there might be ice on the walls of those craters. Sunlight never penetrates into the craters, so that would be an exciting cache to study someday.  The water could be from impacts of comets, and studying THAT ice would tell us about the compositions of the comets that left their water behind.

The full imaging mission, which is planned to last for at least a year, begins on April 4; currently scientists and engineers are testing the spacecrafts systems and instruments to see how it is responding to its permanent home in orbit around Mercury — and enduring the harsh environment so close to the Sun.

Mercury might seem the last place you’d want to visit — and it probably won’t be the subject of human exploration for a long time. It’s a pretty extreme place, experiencing the widest surface temperature swings of any place in the solar system. It has little to no atmosphere, and its surface takes a radiation pounding from the Sun. Still, if you’re going to completely understand the solar system you inhabit, it pays to study the extreme places as well as the temperate (relatively) ones. In Mercury’s case, astronomers have a very specific set of questions to ask to help understand this place:

Why is Mercury so dense?  What is its geologic history? What is the nature of its magnetic field? What is the structure of the planet’s core? What are the unusual materials seen at the poles?  What volatiles (gases) are important at Mercury?

Some of these questions are those you’d ask at any planet to help you understand its composition and history.  So, with Mercury, we’ll finally get some closure on the last of the major planets of the solar system.  The only remaining world to visit (and there’s a spacecraft on the way) is dwarf planet Pluto. New Horizons will give it a swing-by in 2015, on its way out to explore the outer solar system. Another extreme, to be sure, but now we’ve got precedent with Mercury.