Flying over the frigid northern reaches of Mars, the orbiting Mars Express satellite captured images of the 50-mile wide Korolev crater filled with ice.

Korolev is an especially alluring sight, not just because it's a well-preserved impact crater but because it's loaded with ice over a mile deep year round.

Launched 15 years ago by the European Space Agency (ESA), Mars Express often focuses on glaciers and ice in the Martian polar regions.

The Korolev crater's ice is resistant to melting during the warmer summer seasons because the massive plain of ice creates a "cold trap," ESA explains. When air travels above the crater, it cools and sinks over the ice, building a sort of cool "shield" over the ice.

The Mars Orbiter looking down upon the Korolev crater. Image: esa

So even as the seasons change, Korolev remains brimming with ice. Most Martian craters, even in cooler regions, don't remain full year-round.

As Mars Express zips over the desert planet, it takes photos of different strips of land, and then transmits the pictures back to Earth.

ESA scientists then combine the images together to build a coherent picture of different Martian landforms, dried-up lakes, and masses of frozen water.

These Korolev images above are composites of five different photos, each taken during a separate orbit across Mars.

Korolev is named for a giant in space history: rocket scientist Sergei Korolev.

Korolev headed the Soviet space program and famously beat the Americans into space. The Soviets, under Korolev's leadership, sent both the first human and satellite into space.

"He’s a key figure in space history — though he died much too early," space historian Robert Pearlman said.

Mars Express continues to actively scour the red Martian terrain and transmit truly brilliant extraterrestrial images back to Earth.