Four side-by-side images, overhead views of different landscapes on Mars: The first image shows a flat area with a few small craters. The terrain around the edge of the frame is a dull copper color, while the rest is very bright, in shades of very light green and turquoise. The second image appears to be a crater or valley, but looks like the right half of a sunflower bloom, although colored in shades of tan and brown, except for the petals at the top of the frame, which are highlighted in very light shades of mint green. The third image shows a much more uneven and rocky surface, with rust-colored craters and outcroppings; on each of those the south-facing edges are dabbed with higlights of whitish light blue. The fourth image is of mostly flat ground, colored a dull copper, resembling a face with rocky outcroppings creating two eyes up top, a nose in the middle, and a crooked mouth at the bottom of the frame. The eyes shine brightly and the nose is highlighted slightly in bright blue, coloring the south-facing slopes.
Martian surface frost, made up largely of carbon dioxide, appears blueish-white in these images from the Thermal Emission Imaging System (THEMIS) camera aboard NASA’s 2001 Odyssey orbiter. THEMIS takes images in both visible light perceptible to the human eye and heat-sensitive infrared.

Mapping Martian Ice

While Mars no longer has lakes and rivers as it did in the distant past, Mars still has abundant water in the form of ice. This ice moves back and forth between Mars' polar caps, the atmosphere (as fogs, vapor, and clouds), and the surface (as frost and ground ice). Learning more about the planet's current water cycle helps scientists understand the workings of a dusty, icy planet and how it has changed over time. Early in Odyssey's mission, the orbiter mapped water signatures in the top 3 feet (1 meter) of the surface using its gamma-ray spectrometer suite, revealing large expanses of near-surface water ice in the high latitudes of Mars. This hidden water reservoir was later confirmed by NASA's Phoenix lander, which dug into the surface and struck the predicted ice layer.

Odyssey's THEMIS (Thermal Emission Imaging System) instrument, which sees the planet in visible and infrared light, has been tracking water by observing the planet in the frigid early morning, when its valleys are filled with fog, clouds accumulate on its high mountains, and parts of its surface are covered in a layer of overnight frosts of water and dry ice.

Understanding the Martian water cycle provides insights into how water moves around the planet and is affected by the tilt of Mars. Information gathered helps us better understand the history and activity of water through the eons on our home planet, Earth. This also helps plan for future human Mars missions, which will require water for astronauts.

An overhead view of the Martian surface shows a very large crater dominating the center of the image, colored turquoise around its rim and walls, and one the uneven ground extending toward the upper left and below the crater in the frame. The floor of the crater is deep orange, and the rest of the surrounding terrain, mostly flat with a few small craters, is colored in various shades of orange and golden yellow.
Terra Sirenum: This false-color mosaic image combines separate frames taken by the Thermal Emission Imaging System (THEMIS), a special camera on NASA's Mars Odyssey orbiter. On the southwest edge of the immense volcanic region of Tharsis, lava from its giant volcanoes flowed down to meet the old cratered landscape of Terra Sirenum. Scientists cannot say how many years separate the flows from the terrain they engulfed, but the relationship between the two tells a complex tale.
NASA/JPL-Caltech/University of Arizona

Determining the Composition of Mars

Odyssey's extensive observations of the Martian surface have helped scientists piece together information about the planet's history. One of Odyssey's major contributions to Martian science was a detailed global map of Mars created using thousands of images from its THEMIS instrument. THEMIS was designed to measure surface temperatures over the course of multiple nights and days during repeated passes over Mars. This has helped pinpoint the locations of rock, sand, and dust, and map craters, valley networks, sandstone, salts, and iron-rich rock. THEMIS also identifies minerals on the Martian surface that other spacecraft cannot see. Meanwhile, Odyssey's GRS instrument mapped the elements that are on the Martian surface. Together, the instruments revealed unique information about the makeup of Mars.

These six views of the Martian moon Phobos were captured by NASA's Odyssey orbiter as of March 2020. The orbiter's infrared camera, the Thermal Emission Imaging System (THEMIS), is used to measure temperature variations that provide insight into the physical properties and composition of the moon. The views represent waxing, waning and full views of the moon. THEMIS infrared images are colorized and overlain on THEMIS visible images taken at the same time. Phobos is about 15 miles (about 25 kilometers) across.

Observing Mysterious Moons

Odyssey's THEMIS camera, used extensively to observe the Martian surface, has also captured new views of Phobos and Deimos, two moons of Mars. By studying temperature variations on each moon, we now know much more about surface materials and their characteristics. This type of information helps scientists in their quest to determine whether the moons are chunks of Mars launched into orbit above the planet by an ancient collision, or whether they are captured asteroids.

A gold-colored spacecraft orbits over Mars, with a dish antenna extending from its top, a spindly boom extending from the front of it toward the viewer, and a large three-paneled solar array attached vertically to its left side. Mars appears as a dusty tan color covering the lower half of the frame, with patches of white at its top, against a black sky flecked with stars in the upper frame.
NASA's Mars Odyssey spacecraft passes above Mars' south pole in this artist's concept illustration. The spacecraft has been orbiting Mars since Oct. 24, 2001.

Beaming Science Back to Earth; Helping Future Human Missions

Even when it hasn't been transmitting its own science data back to Earth, Odyssey has sent back data from other missions via its participation in the Mars Relay Network. This capability has been extremely valuable, because an orbiter can carry radios and antennas that can send and receive more data than a spacecraft on the surface of Mars. Odyssey has been a messenger from Mars routinely through the years with NASA's rovers, enabling scientists to get data from the Mars surface much faster, and speeding up the process of sharing Mars images with the public.

Another Odyssey activity will benefit future human Mars explorers. By recording the radiation environment from its low orbit over the planet, the spacecraft has helped determine radiation risks that could face humans who may someday go to Mars.