Mercury Dual Imaging System (MDIS)
The Mercury Dual Imaging System (MDIS) consists of a pair of color cameras—a narrow angle imager and a
wide angle imager—which will take pictures of Mercury in visible and near-infrared light. Many images
will be captured during the flybys, and more detailed pictures will be taken during the time in orbit
(one Earth year). In total, the cameras will image the entire planet twice to create global topographic
maps of Mercury.
How it works
First, light must enter MDIS through a small (12 cm x 12 cm) window, where filters allow only the
visible and near-infrared wavelengths of light to pass. From there the light can enter either camera,
although only one may operate at a time due to temperature constraints.
The wide angle camera takes pictures with a larger field of view, but with less detail. This camera
employs 12 different filters to better define the light that enters it over a range of different
wavelengths. Different wavelengths of light can provide information about the composition of a feature,
as well as its thermal properties.
For example, the images
of the Old Faithful Geyser at Yellowstone National Park, at right, were taken using a visible light
filter (top) and an infrared light filter (bottom). The infrared image reveals that the water erupting
from the geyser is hot (red and white areas), while the surrounding ground is cooler (bluer areas).
Additionally, light in different wavelengths can be combined to produce color pictures. Your television
uses red, green, and blue filters in concert to create the image you see on the screen.
Images obtained through different filters in the MDIS wide angle camera will provide information about
the composition of the rocks on the surface of Mercury, allowing us to understand more about the
geological processes which have taken place there.
about filters and color here!
The narrow angle camera has a smaller field of view, and therefore can take more detailed pictures of
landforms and surface features. This imager has only one visible light filter.
Both cameras store images using technology similar to fax machines, scanners, and digital still or
video cameras. Images are recorded using charge-coupled devices (CCDs), which consist of many, many
(e.g., up to 16 million!) small pixels or light-sensitive squares. Light strikes these tiny pixels,
causing an electric charge to build up that is proportional to the intensity of the light. Data from
all of the pixels is stored in this digital form.
(Image credit, left: NASA/GSFC/LaRC/JPL/MISR Team; Image credit, right: NASA)
The pictures above are both digital images of Earth’s Moon. The picture on the left has only about
140 pixels per row and column (a total of 140x140 = 19600 pixels), whereas the picture on the right has
almost 2,000 pixels per row or column (4 million pixels). It’s easy to see how increasing the number
of pixels increases the amount of detail in the image.
Both of the MDIS cameras have 1024 pixels in each column and 1020 in each row, for a total of over a
million pixels per image.
Learn more about CCDs here!
Contribution to our understanding of Mercury and beyond
Presently, only 45% of Mercury has been photographed via spacecraft; Mariner 10 orbited Mercury in
1974, capturing black and white photographs of the planet. We have yet to see an entire hemisphere of
Mercury! The MESSENGER MDIS will greatly expand our imaging coverage and therefore our knowledge of
Mercury’s surface topography and surface composition. The entire planet will be imaged twice, at two
Photographs will be in color and monochrome, as well as in visible light and near infrared light. Most
of the globe will be photographed from two different viewing angles, allowing stereo maps to be created
(in the same way that each of your eyes sees a slightly different view, and your brain combines these
into a 3-dimensional view). By combining these stereo maps with data acquired by the
Mercury Laser Altimeter, a global topographic map will be constructed.
(Image credits: NASA/JPL)
Several images were combined to create these views of Mars from the
Mars Exploration Rover, Spirit. The image on
the left is a monochrome (black and white), whereas the image on the right is a stereo image. If
viewed through 3-D glasses, the stereo image will appear in 3-dimensions!
Other applications of this instrument
Instruments similar to the MDIS—digital cameras—are used here on Earth to capture photographs of
friends, family, landscapes, and adventures. Sophisticated versions of our digital cameras, such as
the MDIS, are used on virtually every NASA mission.
(Image credits: NASA)
The image on the left is a mosaic of 18 pictures taken by the Mariner 10 spacecraft in 1974. The
image on the right is a 27-picture mosaic taken in 2000 from the Cassini spacecraft, and is
“the most detailed color portrait of Jupiter
ever produced”. Certainly MESSENGER will include in its list of accomplishments the most
detailed portrait of Mercury ever produced!
Working with the other instruments
In order to create an accurate topographic map of the planet, MDIS images will be used with
Mercury Laser Altimeter (MLA) data. In addition, MDIS spectral data will
complement that collected by the Mercury Atmospheric and Surface Composition
Spectrometer (MASCS), the X-Ray Spectrometer (XRS), and the Gamma Ray and
Neutron Spectrometer (GRNS) to reveal surface composition characteristics.