A New View of Olympus Mons

After 100,000 orbits and almost 23 years on Mars, NASA’s Mars Odyssey orbiter has seen a lot. The spacecraft was sent to map ice and study its geology, but along the way, it’s captured more than 1.4 million images of the planet.

A recent image captured the Solar System’s tallest mountain and volcano, Olympus Mons.

This image won’t win any photography contests, but that’s not what this is about. Scientists are experts at extracting information and images like this hold information that’s part of the overall Mars puzzle.

In this image, Odyssey is taking a horizontal look at Mars. The spacecraft usually points down at the surface and captures images in long strips, which is why the image has such an unusual shape. But this horizontal viewpoint is part of an effort to use Odyssey and its Thermal Emission Imaging System (THEMIS) camera to capture high-altitude images of Mars’ horizon.

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

Odyssey captured its first horizontal horizon image in late 2023, and it took engineers three months to get the operation right. THEMIS is fixed in position and points straight down. For these images, the entire spacecraft had to tilt 90 degrees. But it also had to maintain a position where the Sun could strike its solar panels. To accomplish that, Mars Odyssey used its thrusters to orient itself so that its antennae pointed away from Earth. As a result, the spacecraft couldn’t communicate with Earth for the duration of the maneuver.

Orbiters like Odyssey, MRO, and Mars Express have imaged the Martian surface in great detail and given us a vast archive of images. But these images are different. They give scientists a different look at the Martian sky, its clouds, and its dust.

THEMIS is an infrared camera and is designed to sense temperature changes on Mars’ surface. It can differentiate between sand, rock, ice, and dust. By pointing at the sky, THEMIS can measure the presence of ice and dust in Mars’ atmosphere.

Odyssey personnel first realized they could point the spacecraft at the horizon when other missions were landing on the Martian surface. When Curiosity landed in 2012, Odyssey played a key role by relaying information about the landing back to Earth. To do that, it had to orient itself differently, pointing its antenna at the rover’s landing ellipse. While positioning the antenna for that job, scientists realized that THEMIS was pointing at the horizon.

“We just decided to turn the camera on and see how it looked,” said Odyssey’s mission operations spacecraft engineer, Steve Sanders of Lockheed Martin. Lockheed Martin built Odyssey and helps conduct day-to-day operations alongside the mission leads at JPL. “Based on those experiments, we designed a sequence that keeps THEMIS’ field-of-view centered on the horizon as we go around the planet.”

Odyssey has been a definite success by any measure, and it’s still going strong. In fact, it’s the longest continually active mission around another planet. But that feat takes careful planning and operation.

“Physics does a lot of the hard work for us,” Sanders said. “But it’s the subtleties we have to manage again and again.” The spacecraft is solar-powered, and it’s out of direct sunlight for several minutes in each orbit, but the instruments have to be kept in a certain range to remain operational, which means juggling energy demands.

Odyssey also has a limited amount of hydrazine fuel for its thrusters. With no fuel gauge, engineers have to recalculate the amount remaining after each maneuver. One way they do this is by applying heat to the two propellant tanks to see how long they take to heat up. In March 2023, NASA said that the spacecraft has enough fuel to last at least until the end of 2025.

“It takes careful monitoring to keep a mission going this long while maintaining a historical timeline of scientific planning and execution — and innovative engineering practices,” said Odyssey’s project manager, Joseph Hunt of JPL. “We’re looking forward to collecting more great science in the years ahead.”

Odyssey can change its orbit, so there’s no way to calculate exactly how many orbits it has left. But it’s completed over 100,000 in almost 23 years, and it’s likely to complete several hundred more before its hydrazine runs out.