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NASA’s longest-lived Mars robot is about to hit a new milestone on June 30: 100,000 trips around the Red Planet since launch 23 years ago. During that time, the Mars Odyssey 2001 orbiter mapped minerals and ice on the Martian surface, identified landing sites for future missions, and transmitted data back to Earth from NASA’s rovers and landers.

Scientists recently used the orbiter’s camera to take a stunning new image of Olympus Mons, the tallest volcano in the Solar System. The image is part of an ongoing effort by the Odyssey team to provide high-altitude views of the planet’s horizon. (The first of these views was published in late 2023.) Similar to the prospect of Earth astronauts boarding the International Space Station, the view allows scientists to learn more about the clouds and dust in the Martian air.

Taken on March 11, the latest image of the horizon captures the Mount Olympus in all its glory. With a base that stretches 373 miles (600 kilometers), the shield volcano rises to a height of 17 miles (27 kilometers).

“Usually we see the Olympus Mons in narrow strips from above, but by turning the spacecraft toward the horizon, we can see in one image just how large it looms over the landscape,” said Odyssey project scientist Jeffrey Plaut of NASA’s Jet Propulsion Laboratory in South California, which manages the mission. “Not only is the image spectacular, but it also provides us with unique scientific data.”

In addition to providing a freeze frame of clouds and dust, such images, when taken over many seasons, can give scientists a more detailed understanding of the Martian atmosphere.

A bluish-white band at the bottom of the atmosphere suggests how much dust was there in early fall, when dust storms typically begin to rise. The purple layer above this is probably due to a mixture of the planet’s red dust with some bluish water-ice clouds. Finally, toward the top of the image, a blue-green layer can be seen where water-ice clouds reach about 31 miles (50 kilometers) into the sky.

How did they take the picture

Named after Arthur C. Clarke’s classic science fiction novel 2001: A Space Odyssey, the orbiter captured the scene with a heat-sensitive camera called the Thermal Emission Imaging System, or THEMIS, that Arizona State University in Tempe built and operates. But since the camera is designed to look down at the surface, getting a picture of the horizon requires extra planning.

By firing thrusters located around the spacecraft, Odyssey can direct THEMIS to different parts of the surface, or even slowly roll over to view the small moons of Mars, Phobos and Deimos.

The recent horizon image was conceived as an experiment many years ago during the landings of NASA’s Phoenix mission in 2008 and the Curiosity rover in 2012. As with other Mars landings before and after those missions, Odyssey played an important role in conveying data as a spaceship departs for the surface.

To transmit their vital engineering data to Earth, Odyssey’s antenna had to be pointed at the newly arrived spacecraft and their landing ellipses. Scientists were intrigued when they noticed that the positioning of Odyssey’s antenna for the task meant that THEMIS would be pointed at the planet’s horizon.

“We just decided to turn on the camera and see what it looked like,” said Odyssey mission engineer Steve Sanders of Lockheed Martin Space in Denver. Lockheed Martin built Odyssey and helps run day-to-day operations alongside mission managers at JPL. “Based on these experiments, we designed a sequence that keeps THEMIS’ field of view centered on the horizon as we orbit the planet.”

The secret of a long space odyssey

What is Odyssey’s secret to being the longest continuously active mission in orbit around a planet other than Earth?

“Physics does a lot of the heavy lifting for us,” Sanders said. “But these are the subtleties that we have to manage over and over again.”

These variables include fuel, solar energy, and temperature. To ensure Odyssey uses its fuel (hydrazine) sparingly, engineers must calculate how much is left, since the spacecraft has no fuel gauge. Odyssey relies on solar power to run its instruments and electronics. This power varies as the spacecraft disappears behind Mars for about 15 minutes per orbit. And temperatures must remain balanced for all Odyssey instruments to function properly.

“Careful monitoring is required to keep the mission going this long while maintaining a historic timeline of science planning and execution — and innovative engineering practices,” said Odyssey project manager Joseph Hunt of JPL. “We look forward to collecting more great science in the coming years.”