If someone ever figures out a way to mine it, they could become very rich indeed. On Tuesday morning a robot explorer named Messenger will sweep 200 kilometres above the first rock from the sun. (Sydney Morning Herald)
The planet was named Mercury, after the Roman messenger of the gods. However, if the little world has anything to tell us, it has been keeping it very a tight secret. "Mercury," says Nick Lomb, the astronomer at the
Averaging just 58 million kilometres from the sun, it is the most difficult planet to see from Earth. "It never rises very high in the morning sky before sunrise, and sets soon after the sun."
One puzzle is why Mercury, just 4880 kilometres across, is so dense. Scientists estimate an iron-rich core must make up 60 per cent of the planet.
"If Mercury is 60 per cent iron," Dr Lomb said, "then we have 198 million million million tonnes of iron ore. That should be enough for anybody."
With lump iron ore selling for about $US60 ($68) a tonne on world markets, that would make the planet worth $US11,880 million million million.
Some scientists suspect Mercury was once a much larger world that smashed head-on with another planet. Mercury's outer rocky crust was ripped off, leaving the iron core.
Another mystery is its slow rotation. While it whips around the sun in 88 Earth days, 176 pass between one sunrise and the next - so any Mercury resident would enjoy two birthdays every day.
But it is unlikely the planet is inhabited - the temperature soars to 430 degrees during the day and plunges to minus 170 at night.
Despite the searing heat, reflections from radar signals beamed from Earth suggest that deep craters at Mercury's poles, where the blistering sunlight never shines, may be filled with ice.
Mercury has been visited previously by only one spacecraft, NASA's Mariner 10, which flew past the planet more than 30 years ago.