  One of the main objectives of the Mars Exploration Program is to search for
evidence of past or current life on the planet. To achieve this, Mars
exploration has been focusing on regions that may have liquid or frozen water.
A set of critical areas may have seen cycles of ice thawing in the relatively
recent past in response to periodic changes in the obliquity of Mars. In this
work, we use convolutional neural networks to detect surface regions containing
"Brain Coral" terrain, a landform on Mars whose similarity in morphology and
scale to sorted stone circles on Earth suggests that it may have formed as a
consequence of freeze/thaw cycles. We use large images (~100-1000 megapixels)
from the Mars Reconnaissance Orbiter to search for these landforms at
resolutions close to a few tens of centimeters per pixel (~25--50 cm). Over
52,000 images (~28 TB) were searched (~5% of the Martian surface) where we
found detections in over 200 images. To expedite the processing we leverage a
classifier network (prior to segmentation) in the Fourier domain that can take
advantage of JPEG compression by leveraging blocks of coefficients from a
discrete cosine transform in lieu of decoding the entire image at the full
spatial resolution. The hybrid pipeline approach maintains ~93% accuracy while
cutting down on ~95% of the total processing time compared to running the
segmentation network at the full resolution on every image. The timely
processing of big data sets helps inform mission operations, geologic surveys
to prioritize candidate landing sites, avoid hazardous areas, or map the
spatial extent of certain terrain. The segmentation masks and source code are
available on Github for the community to explore and build upon.
