Abstract
Martian ice likely holds the key to interpreting Mars’ past climate, but
much is still unknown regarding the distribution and properties of Mars’
ice deposits. It is well known that Mars has extensive polar ice caps
the size of Greenland. Included in these large polar caps are the north
and south polar layered deposits (NPLD and SPLD, respectively), that are
composed of kilometers-thick deposits of water ice. In addition, surveys
by Conway et al. (2012) and Sori et al. (2019) identified craters in the
surrounding terrains that contain “outlying” deposits of ice, which
may or may not have formed concurrently with the polar caps. There are
many differences between the NPLD and SPLD, including higher dust
content and sequestered CO2 within the SPLD, a younger surface age of
the NPLD, and properties in some locations of the SPLD that causes a
‘fog-like’ scattering in radar observations. These differences between
the NPLD and SPLD may or may not be shared in these outlying deposits,
and may provide clues to the climate conditions under which the PLDs and
outlier deposits formed. We have analyzed a total of 517 SHARAD radar
tracks across 24 ice deposits within craters. For the northern
population, we detected subsurface layers in 3 out of 4 crater deposits.
In the southern population, we detected subsurface layers in 4 of the 20
crater deposits. Of the 4 southern crater deposits that exhibited
subsurface layers, 3 were contiguous with the SPLD. We also found
deposits with radargrams that contain fog, and one that contains a low
reflectance zone. After examining the subsurface radar observations, we
determined that the northern outlier deposits share many common
characteristics with the NPLD, and thus may have a shared depositional
history or at least were emplaced under similar environmental
conditions. The southern outlying crater deposits exhibit a variety of
subsurface characteristics, and likely represent 2 or more populations
that may have differing depositional histories.