The sand dunes on Mars have a secret shimmer. Scientists using Europe's Mars Express spacecraft recently spotted something striking inside a giant crater on the Red Planet: fields of dark, almost metallic-looking waves that stretch for kilometers across ancient Martian ground.
The images, taken October 5, 2025 by the High Resolution Stereo Camera aboard Mars Express, reveal a vast dune field filling Kaiser Crater. This crater sits in Noachis Terra, one of the oldest regions on Mars. Scientists estimate the terrain here has been battered by falling space rocks for roughly 4 billion years.
Kaiser Crater measures about 180 kilometers (112 miles) across and plunges a couple of kilometers deep. That's wide enough to swallow most countries. The crater's southern rim creates a prominent ridge running through the center of the image.
The real star of the show, though, is the shimmering dune field coating much of the crater floor. These aren't tiny sand ripples. The dunes can tower more than 100 meters (330 feet) above the surrounding surface—about as tall as a 30-story building. Some stand alone, while others merge into continuous waves of sand stretching several kilometers.
So why do they look almost metallic? The shininess comes from bright frost deposits that gather on the dunes' south-facing slopes. The frost catches sunlight in a way that gives the sand an almost silver gleam.
Mars has two main types of these wind-sculpted dunes. Barchan dunes are curved and sickle-shaped—the most common dunes on Mars and also found in Earth's Sahara and Namib deserts. Transverse dunes run longer and more parallel, forming as barchans collect more and more sand over time. Both types form when winds blow from the same direction year after year, gradually piling sand into ridges.
The images captured by Mars Express have a ground resolution of about 17 meters per pixel, giving scientists a detailed view of this ancient landscape. The spacecraft has been orbiting Mars since 2003, but the planet never seems to run out of surprises.
For planetary scientists, these images offer clues about Mars's climate history and how wind has shaped its surface over billions of years. The dunes tell a story of patient, constant forces—wind and frost working together over millennia to carve patterns no human hand made.