March 16, 2011. Copyright 2011, Graphic News. All rights reserved 

Messenger’s journey to inferno’s edge

LONDON, March 16, Graphic News: NASA’s Messenger spacecraft will enter orbit around Mercury at 00:45GMT on Friday, March 18, becoming the first spacecraft ever to orbit the innermost planet. 

Since its launch in August 2004, Messenger -- standing for MErcury Surface, Space ENvironment, GEochemistry and Ranging -- has travelled some 7.9 billion kilometres, making 15 loops around the Sun and flybys of Earth, Venus and Mercury itself to accelerate the craft to catch up with Mercury.

Deep in the sun’s gravitational grip, Mercury careens around the edge of the inferno in just 88 Earth-days at an average speed of 170,600km/h.

Entering orbit will be “the culmination of the mission, the principle objective,” said Sean C. Solomon, speaking at the annual meeting of the American Association for the Advancement of Science in February.

“We can look forward to an enormous increase in understanding of one of our nearest planetary neighbours,” said Solomon, principal investigator of the Messenger mission.

One of the most exciting questions Messenger might answer is whether Mercury, like the moon, hides water ice in its shadowed impact craters. Mercury’s surface is baked by temperatures of over 370 degrees Centigrade at its equator but craters near the poles are in permanent shadow at minus 183 degrees.

“They don’t see the sun for millions, probably billions of years,” Solomon said. “They’re very cold -- cold enough to preserve water ice for geologically long periods of time.”

If all goes to plan, Messenger’s 12-hour orbit around Mercury will be very eccentric, with its low-point skimming just 200km above the surface and a high point out at more than 15,193km.

Messenger’s payload includes narrow and wide angle cameras and a laser altimeter to map Mercury’s surface, and spectrometers to probe the composition of the rocks and the planet’s tenuous atmosphere.

A magnetometer will study how the magnetic field -- springing from its outsized molten metal core, which makes up 60 percent of the planet’s mass -- interacts with the solar wind.

Once in orbit, Messenger will start returning images by April 4. It will stay in orbit for four of Mercury’s 88-day years -- one Earth year -- although the mission could be extended for another year or two if NASA’s budget allows. When fuel or funding runs out, the spacecraft will crash into Mercury’s surface. 
/ENDS