Washington: The gully patterns have provided a deeper insight into the climate of the "Red planet."
Geologists from Brown University have found new evidence that glacier-like ice deposits advanced and retreated multiple times in the mid-latitude regions of Mars in the relatively recent past.
The researchers looked at detailed images taken by NASA's High Resolution Imaging Science Experiment (HiRISE) of 479 gullies in the mid-latitudes of Mars' southern hemisphere. The gully systems, which form on steep crater walls, consist of an alcove at the top from which sediment was excavated, a channel through which material was carried, and a delta-like fan at the bottom where material was deposited.
They concluded that many of those gullies were formed by meltwater from icy deposits, which are known to have covered the Martian mid-latitudes within the last 2 million years.
The study also turned up evidence of multiple gully-forming events, suggesting that these ice deposits waxed and waned several times over the last several million years, relatively recently in Mars' 4.5-billion year history.
The survey showed gully systems in various states of erosion and degradation. In some places, older gully fans, eroded over many years by the elements, had been crosscut by new gully fan systems.
That suggested that at least two gully-carving events. In other examples, gully fans were clearly visible, but the alcoves and channels that supplied them had disappeared, covered by a new layer of ice-rich soil. That too suggested that multiple periods of glacial deposition.
The work also bolstered the idea that many of the gullies were carved by flows of liquid water. In recent years researchers have shown that some of these gully systems are still active today, when the flow of liquid water was unlikely.
The present-day activity was likely driven by CO2 frost, which evaporates from the soil causing rock and rubble to slide down slopes. But this latest study showed that gullies were active when obliquity was higher and CO2 frost would have been sparse. And the association of gullies with ice-rich deposits strongly suggested that water carved these older gullies.
Brown geologists James Head said that this and other research pointing to relatively recent ice ages on Mars suggested that the mid-latitudes of Mars could be a place to look for signs of past life.
The study is published in the journal Icarus.
