NASA’s Mars Odyssey spacecraft launched 20 years ago on April 7, making it the oldest spacecraft still working at the Red Planet. The orbiter, which takes its name from Arthur C. Clarke’s classic sci-fi novel “2001: A Space Odyssey” (Clarke blessed its use before launch), was sent to map the composition of the Martian surface, providing a window to the past so scientists could piece together how the planet evolved, acts as orbiting communications link for other spacecraft, and helps to find safe landing sites for other Mars missions.
“Before Odyssey, we didn’t know where water was stored on the planet,” said Project Scientist Jeffrey Plaut of NASA’s Jet Propulsion Laboratory in Southern California, which leads the Odyssey mission. “We detected it for the first time from orbit and later confirmed it was there using the Phoenix lander.” Apart answering some geological questions, the discovery of water ice is needed to help future astronauts survive on Mars and to provide fuel for their spacecraft. The feasibility of humans traveling to Mars was also the focus of an instrument aboard Odyssey that measured how much space radiation astronauts would have to contend with before it stopped working in 2003.
The orbiter finds the water ice using its gamma-ray spectrometer (GRS) detector, which measures near-surface hydrogen—a proxy for water ice. The GRS measures the amount of different elements on the Martian surface and also serves as a node in NASA’s interplanetary gamma-ray burst (GRB) detection network, which identifies source locations of GRB’s for follow-up astronomical observations.
For many years, the most complete global maps of Mars were made using Odyssey’s infrared camera, called the Thermal Emission Imaging System, or THEMIS. The camera measures the surface temperature day and night, allowing scientists to determine what physical materials, such as rock, sand, or dust, exist. Its data reveals the presence of these materials based on how they heat up or cool down over the course of a Martian day.
Thanks to THEMIS data scientists not only mapped the Martian terrain, they’ve also been able to spot sandstone, iron-rich rocks, salts, and more—findings that help lend deeper insight to Mars’ geological history.
THEMIS has sent back more than 1 million images since it began circling Mars. The images and maps it’s produced highlight the presence of hazards, such as topographic features and boulders, but they also help ensure the safety of future astronauts by showing the location of resources such as water ice. This aids the Mars science community and NASA in deciding where to send landers and rovers—including the Perseverance rover, which touched down on February 18, 2021.
From early on, Odyssey has served as a long-distance call center for NASA’s rovers and landers, sending their data back to Earth as part of the Mars Relay Network. The idea goes back to the 1970’s, when the two Viking landers sent science data and images by short-range radio frequencies to the orbiter, who relayed the data back to Earth. An orbiter can carry radios or antennas capable of sending back more data than a surface spacecraft. But Odyssey made the process routine when it began conveying data to and from NASA’s Spirit (active 2004-2010) and Opportunity (2004-2018) rovers.
Odyssey has supported over 18,000 relay sessions. These days, it shares the communications task with NASA’s Mars Reconnaissance and MAVEN Orbiter, along with the ESA (European Space Agency) Trace Gas Orbiter.
Odyssey has done such a thorough job of studying the Martian surface that scientists have started turning its THEMIS camera to capture unique views of Mars’ moons Phobos and Deimos. As with the Martian surface, studying each moon’s thermophysics helps scientists determine the properties of materials on their surfaces. Such information can offer glimpses into their past: It’s unclear whether the moons are captured asteroids or chunks of Mars, blasted off the surface by an ancient impact.
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