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I am currently studying what we think is a thick (10s of meters), extensive layer of subsurface ice in Arcadia Planitia, Mars. We are probing this layer by combining two data sets: imagery of terraced craters and SHARAD radar data.
Terraced craters indicate layered target material while SHARAD radar reveals reflections in the subsurface. Combining the data will allow us to constrain the properties, and map the variations, of this layer across the region.

Terraced Craters

An example of a crater with two terraces.
HiRISE Image ESP_018522_2270
"Badger" Crater is an example of a terraced crater with a diameter of ~710 m. This crater has two terraces: a shallow, smaller terrace and a wider, deeper terrace above the "nested crater" which gives it the appearance of a bullseye. However, this crater did not form due to a lucky, second strike in the middle of a preexisting terraced crater. It got this shape because of layers that existed in the target material when the impact occurred. Note that the nested crater is slightly offset from center. This has been proposed to be due to an oblique impact (see J. Ormo, A.P. Rossi & K.R. Housen, Meteoritics & Planetary Science, 48, Nr 3, 403-419 (2013)).

SHARAD Reflections
Example of a SHARAD Radargram
This is an example of a SHARAD radargram in Arcadia Planitia showing reflections due to the interface with the surface and a subsurface interface. This subsurface reflection was first documented by Plaut et al. in their 2009 LPSC abstract "A widespread radar-transparent layer detected by SHARAD in Arcadia Planitia, Mars." The subsurface interface is what we are interested in studying, as it appears to be related to a widespread subsurface layer in the region. The horizontal axis is distance along the track while the vertical axis is time.

This layer of ice....
... is puzzling. Mars' obliquity goes through extreme variations compared to Earth's due to the fact Mars doesn't have a large, stabilizing moon like Earth does. These obliquity variations can drive large-scale climate change, including water ice migration. At high obliquities, ice can move to lower latitudes. However, in recent times, the obliquity has been lower making ice unstable at the mid-latitudes. These recent periods of ice instability mean the ice should not even be here today and would have to be quite old (coming from those periods of high obliquity). What could have kept this ice from disappearing during the recent low obliquity times?