If you might have seen images like the ones above on Planet Four: Terrains and wondered what’s going on with these banded features in these images. That’s the South Polar Layered Deposits (SPLD). The SPLD are alternating layers of ice and dust, giving it that banded look. The are thousands of layers contained in this ~3km geologic unit. The SPLD has a counterpart in the North, unshockingly known as the Northern Polar Layered Deposits (NPLD). The SPLD (like it’s northern sibling) are mostly composed of frozen water ice in between the dust layers.

It is thought that the alternating layers are telling us that these formed from a cyclic climate process. Mar’s obliquity (axial tilt) has changed dramatically over time. The Moon prevents the tilt of Earth from changing significantly from 23.5 degrees, but Mars does not have a large moon. Instead for Mars, the axial tilt can change up to about 60 degrees. Like on Earth, the reason for seasons on Mars is the axial tilt. The more extreme the axial tilt, the more extreme the season are. Climate scientists think that the SPLD formation is related to the changing axial tilt of Mars.

Researchers are still learning about the properties of the SPLD and what it tells us about Mars’ climate history. In 2011, the ground penetrating radar measurements from Shallow Radar (SHARAD) instrument on Mars Reconnaissance Orbiter (MRO), the same orbiter that provides the images we show on the Planet Four projects, uncovered a large carbon dioxide ice reservoirs hidden, lurking below the surface of the SPLD

Here’s a high resolution view of the SPLD from the HiRISE camera: