Swift Mercury gives up its secrets

When ancient astronomers observed the tiny planet that lives on the doorstep of the Sun, they saw how quickly it seemed to shoot across the heavens. So the Romans named it after the god Mercury – the speedy, winged sandal-wearing messenger. When the scientists of the 21st century decided to send the first spacecraft to orbit around Mercury, they saw no reason to break the tradition so they named the craft Messenger.

The mission was launched in 2008 and, since moving into orbit a little over a year ago, the spacecraft has captured nearly 100,000 images and revealed new information about Mercury, which, even thousands of years since its discovery, has always been one of the least understood planets in our
solar system.

The reason we know so little about Mercury is simple – it is uncomfortably close to the Sun. It is difficult to study from afar because telescopes like Hubble are blinded by the Sun’s glare and any probe sent to Mercury must contend with temperatures that swing from a searing 360C (680F) to an unbearable -160C (-256F).

Only one craft has ever been sent to photograph Mercury – Mariner 10 – and it didn’t dare hang around.

Nasa had to make do with a handful of images snapped as the spacecraft whizzed past.

Thirty years after Mariner 10, Messenger was sent to shed light on thismost illuminated of planets. After a year in orbit, the craft’s findings – published in the journal Science – reveal Mercury as a most surprising and complex little world.

Data from Messenger has allowed scientists to build the first precise model of Mercury’s gravity field that, combined with topographic data, has revealed what the planet’s internal structure consists of.

This information has revealed Mercury’s enormous core (relative to the planet’s size) is unlike anything in the solar system. It accounts for 85 per cent of the planet and consists of a solid iron core, sitting within a ball of molten iron and encased by a sphere of solid iron sulphide (sort of like a
giant iron Ferrero Rocher chocolate...or Ferrous Rocher).

Perhaps most surprisingly, the craft also seems to have found that, despite the planet’s proximity to its fiery neighbour, there may be water hiding at Mercury’s poles.

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