Sheyna Gifford

Sep 27th 2021

The Geology of Mars: How Eyes in the Sky Lead to Boots on the Ground


For millennia, we studied the world without the benefit of a view from orbit. Then, in 1947, a camera flew 100 miles above ground. In an instant, our view expanded by far more than the millions of square miles captured in four black and white frames.

The era of studying objects in space via remote sensing continues to this day, with the aid of detailed maps using visual, thermal and chemical data. The blue dunes — constructed images celebrating the Odyssey orbiter’s 20th anniversary — demonstrate how remote sensing satellites not only show us the geology of Mars but also allow us to map out future missions there.

A Deceivingly Simple Mission

At first glance, the Mars Odyssey explorer has a straightforward-sounding mission: to detail the amount and distribution of chemicals and minerals in the Martian surface. To do this, Odyssey first flew 200 days through deep space. Then, since real-time remote control from Earth isn’t possible 150 million kilometers (93 million miles) from Earth, it followed pre-written instructions: Slow down from 5.4 km/sec (12,000 mph) to 4.3 km/sec (10,000 mph). Insert into orbit. Photograph the same amount of land as the Earth using three instruments. Find water, if possible, and anything that might have been shaped by water. Look for hydrogen and other chemicals, too. And don’t crash.

Simple and to the point — but far from easy.

Twenty years ago, the imperative to go make a map of Mars came with a high risk of failure. Prior to Odyssey, 30 total missions from the U.S., Russia and Japan attempted to reach Mars. Only 10 managed to return images. Most either exploded on the launch pad, malfunctioned in transit or missed Mars entirely. The two missions immediately prior to Odyssey didn’t miss the planet enough. Mars Climate Orbiter and Mars Polar lander were destroyed on arrival. By the time Odyssey came along, NASA needed to stick the Mars landing — not just for the sake of the eponymously named orbiter.

When Odyssey successfully took up its survey of the red planet, the Spirit and Opportunity rovers were less than two years from launch. They would be the first Mars rovers since Sojourner in 1996. The maps they would use to land in 2004, made by Mars Global Surveyor (MGS), showed that many surface features seemed to have been made by flowing water, some of which seemed to still be on the move. Gullies were clearly seen changing shape from one year to the next. MGS images also showed boulders the size of houses in some areas. Spirit and Opportunity intended to avoid those as well as smaller obstacles during landing. But for that, they would need better maps. Much better maps.

Thanks in part to Odyssey, both Spirit and Opportunity (or Oppy, as the rover came to be called) managed to avoid giant boulders and other calamities. The two rovers went on to exceed their original mission by more than a decade. That time was spent investigating the geology of Mars up close, observing targets picked by Odyssey and MGS scientists as possibly water-made or even water-containing. From 400 km (250 miles) up, Odyssey identified sites of interest not only by physical appearance but also by temperature and what each structure contained. That’s where the blue dunes come in.

Cold Contrast

While not actually blue in any way, shape or form, the false-colored dunes are in fact much colder than the surrounding dunes at Mars’ northern polar cap. From an exploration standpoint, that’s very interesting. Water ice trapped there wouldn’t sublimate as frequently, making these dunes a potential target for finding the much-sought-after stuff of life. Then again, their lower temperatures indicate that the sun doesn’t reach there for as long or as often. Robotic explorers counting on solar power might well run out of juice before completing their study. It might take a remote sampling mission like Mars Ingenuity, an explorer powered by something other than sunlight or even a person to find out if these colder dunes hold the substance we’ve been seeking all over the planet for half a century.

The long-term goals of Mars exploration are many and stacked: Find the water and look for life. Extract the water on Mars to make fuel supplies and air. Feed the habitat’s plants and people. For our dreams to come to pass, we first have to find a large, accessible supply of water — or, more likely, more than one. Enhanced-color images like the blue dunes highlight changes in geomorphology that guide major decisions about planetary exploration.

Given how much we know about Mars today from the cameras mounted on MGS, Mars Odyssey and Mars Reconnaissance Orbiter, it’s amazing to think that the Solar System Exploration Committee argued against sending a mission to Mars with a camera onboard. The reason? In the 1990s, the images gathered from Viking in the 1970s were believed to be good enough for future mission planning. This line of reasoning appears now and again, most recently with the Juno mission to Jupiter. JunoCam, the onboard camera, isn’t even listed as a scientific instrument. Image processing from JunoCam has been outsourced to the public. Analysis from JunoCam and the handful of active Mars Orbiters is still taking place at NASA.

In the near future, the distant dunes may be colored in by anyone with the curiosity, will and talent to make their mark on Mars exploration.

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