This was
your sky.

The Dotted Dunes of Mars

As spring arrives in Mars's northern hemisphere, dark spots appear on the dunes near the poles. These spots are areas where thin ice thaws first, revealing the darker sand beneath. The dark sand absorbs more sunlight, accelerating the thawing process. By summer, these spots expand, and the entire dunes become dark and thawed, as carbon dioxide and water ice sublime directly into gas.