A new view of Olympus Mons


After 100,000 orbits around Mars and nearly 23 years of stay, NASA's Mars Odyssey orbiter has seen a lot. The spacecraft was sent to map the ice and study its geology, but during that time it took more than 1.4 million images of the planet.

A recent photo captures the solar system's tallest mountain and volcano, Olympus Mons.

This photo won't win any photography contests, but that's not what this is about. Scientists are experts at extracting information, and photos like this contain information that is part of the whole puzzle of Mars.

In this photo, Odyssey is looking horizontally at Mars. The spacecraft usually points down at the surface and takes pictures in long strips, which is why the shape of the photo is so unusual. But this horizontal view is part of an effort to use Odyssey and its Thermal Emission Imaging System (THEMIS) camera to take high-altitude pictures of the Martian 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 just how large it appears on 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, but it also provides us with unique science data.”

Dust storms typically begin during Martian downpours, and the bottom blue layer is dust in Mars' atmosphere. Above that is a purple layer. This is where red dust from the planet's surface mixes with blue water ice. The uppermost blue-green layer is where water ice clouds reach up to 50 kilometers (31 miles) into the sky. Image credit: NASA/JPL-Caltech/ASU
Dust storms typically begin during Martian downpours, and the bottom blue layer is dust in Mars' atmosphere. Above that is a purple layer. This is where red dust from the planet's surface mixes with blue water ice. The uppermost blue-green layer is where water ice clouds reach up to 50 kilometers (31 miles) into the sky. Image credit: NASA/JPL-Caltech/ASU

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

Orbiters like Odyssey, MRO and Mars Express have taken very detailed images of the surface of Mars and given us a huge collection of images. But these images are different. They give scientists a chance to see the Martian sky, its clouds and dust from a different perspective.

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

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This is Odyssey's first image of the Martian atmosphere from a horizontal perspective. It was taken from about 250 miles above the Martian surface — about the same altitude at which the International Space Station orbits Earth. Image credit: NASA/JPL-Caltech/ASU

Odyssey personnel first realized they could point the spacecraft toward the horizon when other missions were landing on the Martian surface. When Curiosity landed in 2012, Odyssey played a key role by sending 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 THEMIS was pointing toward the horizon.

“We decided to just turn the camera on and see what it looked like,” said Steve Sanders of Lockheed Martin, Odyssey's mission operations spacecraft engineer. Lockheed Martin built Odyssey and helps with day-to-day operations along with the mission lead at JPL. “Based on those experiments, we designed a sequence that keeps THEMIS's field of view centered on the horizon while it moves around the planet.”

Odyssey has been a definite success by any measure, and it's still going strong. In fact, it's the longest continuously active mission around another planet. But this feat requires careful planning and operations.

“The physics does a lot of the hard work for us,” Sanders said. “But we have to handle the subtleties again and again.” The spacecraft is solar powered and for several minutes on each orbit it is out of direct sunlight, but the instruments have to be kept within a certain range to stay operational, which means balancing 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 it takes them to warm up. In March 2023, NASA said the spacecraft has enough fuel to last at least until late 2025.

An artist's rendering of the Odyssey spacecraft in orbit around Mars. Image courtesy: NASA
An artist's rendering of the Odyssey spacecraft in orbit around Mars. Image courtesy: NASA

“Keeping the mission going for so long while maintaining the historic timeline of science planning and execution requires careful oversight — and innovative engineering practices,” said JPL's Joseph Hunt, Odyssey's project manager. “We look forward to collecting more great science in the years to come.”

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


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