Nasa’s Messenger probe completed a 6,5-year, 8 billion-km journey to Mercury in March. The spacecraft, the first to enter Mercury’s orbit, will spend a year studying the innermost planet in our solar system. – Steve Rousseau
Scientists are intrigued by Mercury because it has a metal-rich core that accounts for about 60 per cent of the planet’s mass, twice that of our solar system’s other terrestrial planets – Venus, Earth and Mars.
How did Mercury form?
There are three competing theories, Messenger principal investigator Sean Solomon says. One proposes that the planet, as it formed from a disc of material spiralling around the Sun, retained metal while slower-moving rockdust particles fell into the Sun. A second theory states that Mercury developed while surrounded by superheated gas that vaporised its crust and much of its mantle. The third holds that a collision stripped the planet of much of its surface, leaving a metal core and mantle much later.
How can this probe settle the debate?
Each theory would leave forensic clues that the probe can identify from orbit. Messenger’s array of spectrometers will determine the composition of minerals on Mercury’s surface.