Probing Mercury

Mercury is the least explored of our solar system's inner planets. To date the planet has been visited by only two spacecraft.

Mariner 10 flew past Venus on 5 February 1974, in order to get a gravity assist to Mercury. It flew by the planet three times between March 1974 and March 1975. Mariner 10 was also the first spacecraft to have an imaging system, and the encounter produced over 10 000 pictures that covered 57 per cent of the planet. Mercury is too close to the Sun to be mapped by the Hubble Space Telescope.

Another NASA spacecraft, called Messenger, was launched on a mission to Mercury on 2 August 2004. Messenger stands for 'MErcury Surface, Space ENvironment, GEochemistry and Ranging'. This probe's seven-year journey will include fifteen trips around the Sun, one Earth fly-by, two

Venus fly-bys, and three Mercury fly-bys (January 2008, October 2008, September 2009) before it enters orbit around Mercury in March 2011. The fly-bys will help focus the science mission when the spacecraft enters orbit. The probe is expected to orbit Mercury for one year. With a package of seven scientific instruments, Messenger will determine Mercury's composition, image its surface globally, map its magnetic field, measure the properties of its core, explore the mysterious polar deposits to learn whether ice lurks in permanently shadowed regions, and characterise Mercury's tenuous atmosphere and Earth-like magnetosphere.

Pictures taken by Messenger in January 2008 show the far side of Mercury contains the wrinkles of a shrinking, ageing planet. There are scars from volcanic eruptions, and craters with a series of troughs radiating from them.

Figure 4.2 The Messenger space probe took this photograph of the far side of Mercury in January 2008. The previously unseen features suggest the planet is old and wrinkly. (Photo: NASA)
Table 4.2 Significant probes sent to Mercury

Name of probe

Country of origin



Mariner 10

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