On Mercury, True North Is Very Close To Magnetic North

A U.S. spaceship early this month raced just 125 miles above the planet closest to the sun, Mercury, and came away with a treasure trove of 1,200 pictures.

The fleet-footed photographer is the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, or MESSENGER, spacecraft.

It snapped closeup pictures of most of the remaining unseen side of Mercury, a blistering hot planet, and gathered other data as well.

This was the second of three flybys that MESSENGER will make, skimming near the planet that is pockmarked with craters, and this close encounter with the planet has given MESSENGER a kick from Mercurial gravitational pull that will help the spacecraft on its journey, which will help it to orbit Mercury beginning in March 2011.

NASA experts have been enthralled with the pictures that MESSENGER has transmitted back to Earth.

For example, a snapshot shows Mercury about 90 minutes after the spacecraft’s closest approach, clearly imaging a bright crater called Kuiper.

NASA has photographed the crater before, but it has been a while, and the earlier picture wasn’t nearly as high quality. That prior picture was taken by the Mariner 10 mission in the 1970s.

The new pics show that for most of the terrain east of Kuiper, toward the limb (edge) of the planet, the departing images are the first spacecraft views of that portion of Mercury’s surface.

Magnetic Personality

Mercury also is highly unusual in how its magnetic field interacts with and magnetic lines in the solar system.

First, magnetic north on Mercury is almost the same, just two degrees different, compared to true north. On Earth, there is an 11 degree difference, according to Brian Anderson, deputy project scientist at The Johns Hopkins University Applied Physics Laboratory in Laurel, Md. He and other experts spoke to space journalists in a teleconference.

Mercury is the planet closest to the sun.

The solar wind that radiates outward from the sun "is directly connected with the planet’s magnetic field, and actually provides direct access to the surface of the planet over large regions of the north and the southern polar region," Anderson said.

There is, he said, "a strong dynamic [interaction] between the solar wind and Mercury’s magnetic field."

The total energy transfer into Mercury’s magnetic field region was perhaps the equivalent of, say, 100 medium-sized power plants," he said.

Data from MESSENGER also show violent volcanic activity, with "explosive eruptions of lava," said Mark Robinson, co-investigator and professor at the Arizona State University.