Since the 1960s and 70s, scientists have considered Mars a "dead planet". As the first close-ups of orbit and surface came in, earlier speculations about canals, water, and a Martian civilization were dispelled. Subsequent studies also showed that the geological activity that spawned features such as the Tharsis Mons region (particularly Olympus Mons) and Valles Marineris had long since ceased.
However, over the past few decades, robotic missions have found ample evidence that Mars is still an active place. A recent clue was an image from the Mars Reconnaissance Orbiter (MRO) showing relatively recent landslides in a crater near Nili Fossae. This area is part of the Syrtis Major region and is located north of the Jezero crater (where the Perseverance rover will land in six weeks!).
The landslide was captured as part of a larger image (see below) captured by the MRO's Context Camera (CTX) on September 21, 2018. The image covers an area almost 5 km in diameter and was taken while the MRO was 284 km above the surface. According to all data, this seems to be due to the fact that material in the crater wall has become unstable.
Landslides in a crater near Nili Fossae on Mars Credit: NASA / UofA HiRiseteam / MRO
The CTX is designed to provide large-scale background views of the terrain around smaller rock and mineral targets that have been examined by other instruments on the MRO – such as the High Resolution Science Imaging Experiment (HiRISE) and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). It is also responsible for capturing mosaic images of large areas to make it easier to choose the landing site for future missions.
Last but not least, the CTX is responsible for monitoring locations on the Martian surface for possible changes over time. This is exactly what this picture showed in a crater wall near Nili Fossae, which has experienced a material fall since the last photograph. The HiRISE camera also noticed a similar incursion of wall material on the other side of the crater.
These features are the result of what geologists characterize as "mass waste processes" (or slope processes). This term is fairly broad and covers the downward movement of rocks and debris, including large landslides, debris avalanches, rockfalls, debris flows, and ground creep. Previous imagery on Mars has shown a whole range of these activities, from giant rock avalanches to tiny collapses and single rock falls.
As already mentioned, the crater recorded in the CTX image lies northwest of the Jezero crater, the landing site of the Perseverance rover. This location was chosen because of the delta fan near the west wall of the crater. On Earth, these features form in the presence of running water, which slowly deposits sediment material over time.
Orbital image of the Jezero crater with its fossil river delta. Photo credit: NASA / JPL / JHUAPL / MSSS / BROWN UNIVERSITY
Like many features in Gale Crater that the Curiosity rover has studied since landing in 2012, this feature is evidence that Mars had flowing water on its surface billions of years ago – in the form of rivers, lakes, and even one great ocean that covered its northern lowlands. If life were to be created around this time, one of the most likely places the petrified remains would be would be Delta fans.
Regardless of whether there was once (or still is!) Life on Mars, what is clear is that the planet is very much alive. Its geological features are evidence of the past and present forces that actively shape it. Understanding these forces and their effects on the landscape is an integral part of our efforts to characterize the Martian environment (and maybe even live there one day).
Further reading: University of Arizona