When Percival Lowell first looked at Mars through his telescope in the 1890s, he saw some remarkable patterns: connecting lines crisscrossing the surface, linking distant ends of the planet in a seemingly non-natural way. Lowell subscribed to Italian astronomer Giovanni Schiaparelli’s interpretation that the lines were canals deliberately constructed by intelligent beings to transport water. And he felt the need to spread the word, writing an increasingly bold trilogy as his convictions deepened: Mars, Mars and Its Canals, and Mars As the Abode of Life.
Several decades later, the Mariner 4 spacecraft flew past the Red Planet, snapping pictures like a speeding paparazzo. The results were disappointing: the grainy photographs showed craters frozen in time, evidence of a brutal bombardment in the planet’s past. And there certainly weren’t any well-constructed canals.
These two examples represent the stark extremes of our perception of Mars, from a world of actively changing surfaces to one of a static, frozen wasteland. Subsequent missions have pointed to a reality that is somewhere in between, but recent findings from NASA’s Mars Reconnaissance Orbiter mission offer unprecedented resolution on dynamic sand dune activity.
Software engineers and image analysts based at the California Institute of Technology, or Caltech, examined pictures from the High Resolution Imaging Science Experiment (HiRISE) camera. This camera is a 30 cm-per-pixel powerhouse that, ironically, is better than publically available images of our own planet. (According to Caltech, images of Earth-based targets taken at a similar resolution are classified information.)
The team looked at HiRISE images taken 105 days apart within the 300 square kilometer Nili Patera dune field and used an advanced processing program to detect subtle changes in dune shape and coverage. To their surprise, they saw movement – up to 4.5 meters – and not just in isolated cases. In fact, according to software engineer Francois Ayoub, who contributed to the study, “in the footprint covered by our analysis, all of the dunes imaged are active. No dune seems static.”
Evidence of morphological changes in the very recent past has been seen before, but the rate and apparent pervasiveness of the dune movement were surprising. As study leader Jean-Philippe Avouac puts it, “wind activity is indeed a major agent of evolution of the landscape on Mars. This is important because it tells us something about the current state of Mars and how the planet is working today, geologically.”
Wind is certainly the most prominent cause of erosion on modern Mars, and the breeze would feel pretty intense to any future Mars-walking astronauts. “Wind speeds on Mars are in the range of speeds found on Earth,” says Ayoub. Based on the HiRISE imagery, “local wind gusts could reach the speed of what would be considered as a hurricane-force on Earth.”
Needless to say, questions remain. Do the dunes creep along the surface slowly and incrementally over several-month periods, or do the shifts represent sudden changes from single wind storms? And just how common are shifting sands?
Fortunately, the Caltech team is already on the case. The software validation shown in this study proves that even more frequent imaging over a larger portion of the planet could provide answers. “A more frequent temporal series of images would be needed,” says Ayoub. “This is something we are working on now as more images are currently acquired.”
The days of planet-paving volcanic eruptions and catastrophic floods may be long past, but Mars remains geologically active as winds continue to re-work the planet’s surface. As the search for signs of life on Mars continues, fast-moving sand dunes suggest that geologically at least, the Red Planet is very much alive.
