NASA's Odyssey, studying Mars' surface

The longest-serving spacecraft at another planet


  • NASA’s Odyssey spacecraft has been orbiting Mars since 2001.
  • Odyssey's original goals were to search for signs of water, make detailed maps of the planet’s surface materials, and determine radiation levels for humans.
  • Today, Odyssey is the longest-operating space mission at another planet. It monitors Mars’ surface changes and is a critical communications relay between surface spacecraft and Earth.

Why do we need Odyssey?

When NASA’s Odyssey orbiter arrived at Mars in 2001, there was only one other working spacecraft at the planet. More than a dozen successful missions have arrived since, yet Odyssey persists, holding the title as humanity’s longest-serving space mission at another world.

Odyssey was an early mission in NASA’s Mars Exploration Program, a multi-decade campaign to understand whether Mars had or still has life. The mission’s original goal was to search for signs of water beneath the surface—a key ingredient for life as we know it. Odyssey was also tasked with mapping the amounts and types of minerals on Mars’ surface, which helps us understand the planet’s history, and measuring the amount of radiation in Mars orbit, which helps us determine the risks to future human explorers.

Odyssey has delivered on those goals. It measured the amount and depth of water ice across the planet, helped us create the most detailed global map of Mars ever, and found landing sites for rover missions where surface materials formed in water. It also showed that radiation levels at Mars are 2 to 3 times greater than those on the International Space Station, and can spike up to 100 or more times greater following solar flares.

Today, Odyssey continues to study Mars’s surface to see how the planet changes over time. The spacecraft also serves as a communications relay to Earth for spacecraft on the surface that lack high-powered antennas and cannot beam information to Earth very quickly. Odyssey transmitted about 85 percent of the data from NASA’s Spirit and Opportunity rovers and continues to serve as a data relay for InSight.

Where the water is on Mars
Water on Mars This map shows how deep water ice is buried beneath Mars' surface, using data from NASA's Odyssey and Mars Reconnaissance Orbiter spacecraft. The outlined box would be a particularly good landing site because it's far enough from the poles to get plenty of sunlight, it's low-elevation which means there's more atmosphere to slow down a spacecraft trying to land, and the water is close enough to the surface to be accessed with a shovel.Image: NASA/JPL-Caltech/ASU

How Odyssey studies Mars

Odyssey carries three science instruments. Its radiation detector, the Mars Radiation Environment Experiment (MARIE), collected 2 years’ worth of data before failing in 2003. Our Sun and other stars emit radiation that can rip through human cells, causing cancer and other health problems.

On Earth, our planet’s magnetic field deflects the radioactive charged particles hurtling at us from space. Mars has no magnetic field, creating a hazard for human explorers that we need to understand and mitigate.

Ironically, that same radiation also helps scientists determine what Mars’ surface is made of. Odyssey’s Gamma Ray Spectrometer (GRS) measures high-energy waves and subatomic particles produced when radiation strikes the surface. The waves and particles contain unique signatures of the rocks they came from, which allows scientists to map the elements that make up the Martian surface and find reservoirs of ice buried just beneath the top layer of soil.

Another instrument, the Thermal Emission Imaging System (THEMIS), takes images of Mars’ surface in visible and infrared wavelengths, allowing researchers to map the planet’s terrain and figure out what minerals make up different landforms. These images were key to finding a landing site for NASA’s Curiosity rover where the rocks appeared to have formed in water.

Mawrth Vallis from Odyssey
Mawrth Vallis from Odyssey NASA's Odyssey spacecraft images Mars' surface in long strips, like this one from a region called Mawrth Vallis. By using different filters and processing the data in different colors, scientists can see subtle differences in surface materials.Image: NASA/JPL-Caltech/ASU

Odyssey and The Planetary Society

Mars Odyssey’s original mission was meant to last less than 3 years, but its longevity has allowed NASA to rely on it as a valuable communications relay for surface missions. The mission's future was thrown into doubt in 2020 when the White House proposed a 3% budget cut to NASA's Mars Exploration Program. That might seem small overall, but the budget cut would have effectively ended the Mars Odyssey mission and deeply impacted the funding for NASA's Curiosity rover. 

Thankfully, this story has a happy ending. The Planetary Society and our members worked with Congress to restore these funds in order to maximize Curiosity’s scientific productivity, continue Mars Odyssey's mission, and generate the highest possible return on investment for U.S. taxpayers.

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