Scientists use a variety of data to study the surface of Mars. Some of the images you see from cameras aboard rovers or satellites orbiting Mars are "visible" images—that is, they approximate what you’d see if you were looking at Mars with your own eyes. However, we can learn a lot more by using images taken at different wavelengths in the electromagnetic spectrum, or by creating visual representations of numerical data. Here are the types of images you will encounter in planning your rover missions:

Visible Image

Visible images cover the wavelength range humans can detect with the naked eye (roughly 400–700 nanometres). Cameras such as the Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) aboard NASA’s Mars Reconnaissance Orbiter, and the High Resolution Stereo Camera (HRSC) on the European Space Agency’s Mars Express spacecraft acquire visible images. The images from these cameras are originally black and white, but you will see colour versions while planning your missions and in Google Earth—these are "false colour" images.

False Colour Images

All colour images consist of 3 "bands": Typically red (650 nm), green (510 nm), and blue (475 nm), as is the case for photos you take with your digital camera. Instead of using red, green, and blue wavelength images for each band, false colour images are created using images taken at a variety of wavelengths. HiRISE false colour images for example are created using red, blue-green, and near-infrared bands.

This allows scientists to distinguish between certain minerals in the image. The image to the right shows a HiRISE image of sand dunes, where the dunes appear dark blue. If you were standing on Mars looking at these dunes, they would not actually look blue to your eyes. In this case, the dark blue of the dunes in false colour tells scientists the dunes are made up of "basaltic" material—sand-sized grains that came from lava that cooled to form rock.

Thermal Infrared Images

Thermal infrared (IR) images give scientists information on the thermal properties of the materials on the Martian surface. This can be used to learn about the composition and grain size of the surface materials. The Thermal Emission Imaging System (THEMIS) aboard NASA’s Mars Odyssey spacecraft takes thermal IR images, some of which you will encounter during your mission planning. Since these are images representing temperature and not what you would see with your eye, lighter areas represent warmer daytime temperatures and dark areas are colder. The THEMIS image to the right shows a large Martian volcano in daytime IR.

Topographic Images

An instrument aboard the Mars Odyssey spacecraft called the Mars Orbiter Laser Altimeter (MOLA) was used to create a global elevation map of the planet. MOLA works by shooting a laser at the surface of Mars and measuring the time it takes for the laser to reflect back to the spacecraft. Since the height of the spacecraft above the surface is known, this time delay can be used to calculate the elevation of each spot the laser hits. Scientists can then take this numerical elevation data and use it to create a visual representation of the elevation (topography) of the planet. The image below shows elevation maps of Mars’ two hemispheres made from MOLA data:

So what am I looking at in Google Earth when I’m planning my missions?

The Mars globe in Google Earth in IMARS displays two types of images: high-resolution CTX visible images (black and white strips) and lower resolution HRSC false colour (the orange background mosaic), marked in the screenshot below.