More than six years after it was launched from Earth, NASA’s MESSENGER spacecraft is set to begin orbiting Mercury on Thursday, the first close rendezvous with the rocky little planet since 1975.
Astronomers are interested in Mercury, the closest planet to the Sun, because it is a terrestrial like Earth, not gassy like Jupiter. There are many such rocky orbs around stars outside our solar system, which means Mercury could offer clues to other worlds as well, NASA said in a statement.
“Now that so many new planets are being discovered around stars in other solar systems, we need to know the effects of space weathering on rocky surfaces so we can accurately interpret telescopic and other remote sensing data we obtain from other rocky or dusty worlds,” said Ann Sprague of the University of Arizona’s Lunar and Planetary Laboratory, one of the scientists working on the project.
MESSENGER — an acronym for MErcury Surface, Space ENvironment, GEochemistry and Ranging — has been journeying toward the planet since August 3, 2004, “dancing” around Earth, the Moon and Mercury itself, mostly to keep it from being drawn in by the Sun’s gravitational pull.
Late on Thursday, the spacecraft will begin its year-long mission around Mercury, orbiting about once every 12 hours and filling in the visual gaps left by the last probe to visit — Mariner 10, which flew by, snapping pictures, in 1974-75.
The spacecraft, with two solar panels for power and a sunshade to keep it cool enough to operate, will study the geologic history, magnetic field, surface composition and other mysteries of this largely unexplored planet. Once the mission ends, the craft will drop to the surface of the planet.
With a diameter just slightly larger than the Moon’s (about 4,800 kilometres), Mercury should have solidified to its core. But the presence of a magnetic field suggests it is partly molten inside.
For decades, scientists who wanted to study Mercury used images made by Mariner 10, which only showed one side of the planet, along with ground-based observations and data obtained from Mars and meteorites.
On the way to Mercury, MESSENGER managed to make pictures of much of what Mariner 10 missed, leaving only about 5 per cent of the planet unseen. Those areas are largely at the poles, and MESSENGER will attempt to make images of them during its orbital mission.
