As the team of scientists behind NASA's MESSENGER spacecraft eagerly awaits the craft's entry into Mercury's orbit on 17 March, we could soon get answers to questions about the origin, composition, interior structure and geological history of this mysterious planet. Louise Prockter, deputy project scientist on the mission, writes in February's Physics World about the challenges the craft has been designed to face, the early successes of the mission and her own triumphant voyage over the past decade's work.
A journey to Mercury faces once-thought insurmountable challenges -- from intense solar radiation, extreme hot and cold, and the need for a seemingly prohibitive amount of fuel to make it to our Solar System's most inner planet. With solar radiation 11 times more intense around Mercury than around Earth, and with temperatures reaching 425ºC on the planet's sunlit surface and dipping as low as -185ºC on its night side, the intricate instruments designed to observe Mercury have much to be protected from.
Prockter describes the design of a sunshield made of heat-resistant ceramic cloth, cleverly crafted to keep almost all the instruments at room temperature, and the highly elliptical orbit the craft will embark upon in order to avoid the solar heat that Mercury's surface radiates back into space.
Following six "gravity assists" -- using the gravity of planets to help tweak a spacecraft's direction, avoiding the need to use prohibitive amounts of fuel -- MESSENGER is more than six years into its journey and soon to embark upon the key part of its mission. Over the last three years, MESSENGER has been using Mercury's own gravity to line itself up for entry into its desired orbit. During this stage of the journey, MESSENGER has already captured shots of Mercury, revealing a hemisphere that had never been imaged before.
These early successes demonstrate the craft's capability and provide early promise of far greater success. On receipt of these early images of Mercury, Prockter writes: "How often in your life do you get to see something completely unexplored?...My first feeling was one of complete joy and disbelief -- a perfect, beautiful, gibbous Mercury filled the screen, showing an incredible level of detail."
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