- The US space agency is set to launch a spacecraft to
Mercury on 2 August, its first visit to the planet in 30 years.
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- The plan is to put the probe in an orbit around the heavy-metal
planet to map its entire surface, study its geology and look for frozen
water.
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- The Messenger spacecraft will make a seven-year journey
that loops around Earth and Venus to get to Mercury.
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- The last Nasa craft sent to the planet was Mariner 10
which sailed past the world three times in 1974 and 1975.
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- Many loops
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- Messenger will not make its first fly-by of the planet
closest to the Sun until 2008, and will not begin its main mission until
2011.
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- Its 7.9-billion-km (4.9 billion miles) trip will see
it loop the Sun 15 times, fly-by Earth once, Venus twice and Mercury three
times.
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- During the Mariner 10 passes, detailed data was only
collected for half of the planet's surface.
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- Messenger (short for MErcury Surface, Space ENvironment,
GEochemistry, and Ranging) will conduct an in-depth study of Mercury in
its entirety. Carrying seven scientific instruments, it will provide the
first images of the whole planet.
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- It will also collect information on the composition and
structure of Mercury's crust, its geological history, the nature of its
thin atmosphere and magnetic field, and the make-up of its core and polar
materials.
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- Sean Solomon, of the Carnegie Institution of Washington,
the lead investigator on the project, described Mercury as unusual among
the inner rocky planets, which include Earth, Venus and Mars.
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- "It is so dense that scientists believe at least
two-thirds of it must be made up of iron. The temperature between day and
night on Mercury varies by up to 600C (1,100F), with a daytime temperature
around 450C (840F)," he explained.
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- Pizza oven
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- The $426m Messenger mission will carry its own sunshade
to protect the craft from the planet's high daytime temperatures, which
are comparable to a pizza oven.
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- Even so, astronomers wonder if there is frozen water
somewhere on the surface despite the heat.
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- "One of the most bizarre questions that has faced
students of the planet Mercury for the last decade is whether the planet
closest to the Sun, with these extreme variations in temperature, might
really have ice lurking in shadowed regions at the poles," Dr Solomon
said.
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- Unlike Earth, Mercury does not spin on a tilted axis,
which means a crater at its north or south pole would be in permanent shadow.
And Mercury's ultra-thin atmosphere does not transport heat from the equator
to the poles, as Earth's does.
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- Dr Solomon said: "The floor of a shadowed crater
would never see the Sun and would be cold enough - minus 180C (300F) or
colder - to freeze water for the lifetime of the planet."
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- Messenger should eventually have company in orbit around
Mercury. BepiColombo, a collaboration between Europe and Japan, is a twin
spacecraft set for launch to the planet early in the next decade.
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- THE PLANET MERCURY * Closest planet to the Sun * Diameter:
4,800KM * Mercurian year: 88 days * Has global magnetic field
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- © BBC MMIV http://news.bbc.co.uk/2/hi/science/nature/3899877.st
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