US: NASA, the US National Aeronautics and Space Administration, launched its first mission in a generation to the planet Mercury early yesterday, one that scientists hope will strip away much of the mystery surrounding the tiny planet closest to the sun.
The Messenger (an acronym for MErcury Surface, Space ENvironment, GEochemistry and Ranging) spacecraft, riding a Boeing Co Delta 2 rocket, blazed across the night sky above Florida's Cape Canaveral Air Force Station as the mission got under way with lift-off at 2:16 a.m. local time.
Among the questions scientists hope to answer is whether Mercury, just slightly larger than Earth's moon, was once Earth-sized itself but lost its rocky exterior either to some cataclysmic collision or to slow ablation by the solar winds.
Scientists also believe there may be frozen water there, trapped in shadowy craters at the planet's poles, never exposed to the sunlight that creates a 1,100-degree Fahrenheit difference between daytime and night-time temperatures on the planet.
"The inner planets (Mercury, Venus, Earth and Mars) all formed from the disc of gas and dust, the solar nebula, that surrounded our young sun.
"They formed by the same processes, they formed at the same time, (but) their outcomes were extremely different. And Mercury is the most extreme of those four planets," said Dr Sean Solomon, principal scientist for the $426 million mission.
Messenger will reach Mercury after a seven-year voyage through the solar system that will take it 15 times around the sun, making near passes of Earth once, Venus twice and Mercury itself three times.
Each planetary pass will act as a gravitational tug to slow Messenger's speed so that it can eventually slip into Mercury's orbit for a year-long study.
The only other close look that planetologists have had of Mercury happened in the mid-1970s when NASA's Mariner 10 spacecraft made three fly-bys.
It photographied about 45 per cent of the planet and discovered that it had a strong magnetic field.
This is an indication, scientists say, that Mercury is about two-thirds iron.
Stormy weather associated with tropical storm Alex, the same system that caused a launch attempt on Monday to be cancelled, kept the launch area closed down for much of the day prior to launch.
But the storm system moved off to the north about an hour before launch, just as forecasters had predicted, NASA said.
Messenger was developed by the Applied Physics Laboratory at Johns Hopkins University in Maryland and is the seventh in NASA's Discovery series of relatively low-cost solar system missions. - (Reuters)