January 22, 2008

Mercury – in Color!

One week ago, the 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 color 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 color views not previously possible. MESSENGER's eyes can see far beyond the color range of the human eye, and the colors seen in the accompanying image are somewhat different from what a human would see.

This color 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 nanometers (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 nanometers. Creating a false-color image in this way accentuates color 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 January 14, 2008, from a distance of about 27,000 kilometers (17,000 miles).

Image sequences acquired through the 11 different MDIS filters are being used to distinguish subtle color variations indicative of different rock types. By analyzing color 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 kilometers (3,030 miles), and the smallest feature visible in this color image is about 10 kilometers (6 miles) in size.

First MESSENGER Spectrum of Mercury

During its flyby of Mercury, the MESSENGER spacecraft acquired the first high-resolution spectra of the planet's surface in ultraviolet, visible, and near-infrared light. The image on the left shows a portion of the ground-track along which the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument accumulated over 650 observations of the surface. The depicted area is about 300 kilometers (190 miles) across. The white track covers about 60 of the MASCS "footprints" or spectral snapshots. The red area highlights about 20 footprints averaged to make the example spectrum on the right, showing the relative amount of sunlight reflected from the surface at wavelengths from the ultraviolet to the visible (rainbow) to the infrared.

The observations were taken on January 14, 2008, beginning as the spectrometer's field of view crossed into the day-lit side of the planet at a distance of about 1,900 kilometers (about 1,200 miles), and continuing until the field of view left the planet at a distance of about 8,500 kilometers (about 5,300 miles) from Mercury. Mercury is about 4880 kilometers (about 3030 miles) in diameter, and the footprints shown here are about 1 by 5 kilometers (0.6 by 3.4 miles).

The Mercury spectrum shows the degree to which different wavelengths of sunlight are absorbed or reflected by its surface materials. Dips in the spectrum indicate where sunlight shining on the surface is partially absorbed. The absorption bands' sizes and colors are diagnostic of the minerals in surface rocks.

While Mercury has been observed telescopically from Earth for centuries, and Mariner 10 took images in one ultraviolet and two color filters when it flew by in 1974 and 1975, MESSENGER is the first mission to observe the surface with enough spatial and spectral resolution to determine Mercury's surface composition.


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