One week ago, NASA's MESSENGER spacecraft transmitted to Earth the first high-resolution image of Mercury by a spacecraft in over 30 years, since the three Mercury flybys of Mariner 10 in 1974 and 1975.
MESSENGER's Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS), is equipped with 11 narrow-band colour filters, in contrast to the two visible-light filters and one ultraviolet filter that were on Mariner 10's vidicon camera.
By combining images taken through different filters in the visible and infrared, the MESSENGER data allow Mercury to be seen in a variety of high-resolution colour views not previously possible. MESSENGER's eyes can see far beyond the colour range of the human eye, and the colours seen in the accompanying image are somewhat different from what a human would see.
The colour image was generated by combining three separate images taken through WAC filters sensitive to light in different wavelengths; filters that transmit light with wavelengths of 1000, 700, and 430 nanometres (infrared, far red, and violet, respectively) were placed in the red, green, and blue channels, respectively, to create this image.
The human eye is sensitive across only the wavelength range 400 to 700 nanometres. Creating a false-colour image in this way accentuates colour differences on Mercury's surface that cannot be seen in the single-filter, black-and-white images released last week.
This visible-infrared image shows an incoming view of Mercury, about 80 minutes before MESSENGER's closest pass of the planet on Jan. 14, 2008, from a distance of about 27,000 kilometres (17,000 miles).
Image sequences acquired through the 11 different MDIS filters are being used to distinguish subtle colour variations indicative of different rock types. By analysing colour differences across all 11 filters, the MESSENGER team is investigating the variety of mineral and rock types present on Mercury's surface. Such information will be key to addressing fundamental questions about how Mercury formed and evolved.
Mercury has a diameter of about 4,880 kilometres (3,030 miles), and the smallest feature visible in the colour image is about 10 kilometres (6 miles) in size.