The red planet Mars seems to be turning blue. The latest image from the European Space Agency's (ESA) Mars Express spacecraft shows what appears to be two deep blue patches on the planet's surface.

The photograph is part of a series of "blue" images taken on the red planet, which include a blue-tinted sunset and blue auroras.

According to the space agency, the blue spots are in actuality layers of dark, volcanic rock being blown by Martian wind. The ESA explained the blue color is an "optical illusion caused by the image processing."

"The blue-hued patches lying within the ragged craters are actually dark sediments that have built up over time," the ESA said.

The latest photograph was taken when the Mars Express passed over Mars' Arabia Terra region, which is known for numerous craters of various sizes. These features on the planet's surface can become eroded over a long period of time.

The ESA said winds on the red planet can reach speeds of up to 62 miles per hour. Winds at these speeds can create massive dust storms that can last for days or weeks. They can also contribute to the erosion of features on the Martian surface over the course of millions of years, sending materials to different parts of the planet.

NASA, together with the European Space Agency and other international space agencies, released images of blue aurorae on Mars.

The phenomenon was first captured on film by the ESA's Mars Express satellite in 2005, and was confirmed by NASA's Maven mission earlier this year.

Through laboratory experiments and analysis of data collected by spacecraft on Mars, NASA scientists were able to identify the blue hue as the "most intense color" of a Martian aurora.

On Earth, an aurora occurs when energy particles from the sun collide with the magnetic field of the planet. These particles are then pulled toward the Earth's poles, where they interact with the upper part of the atmosphere.

The particles from the sun stimulate the neutral particles found in the atmosphere, creating a glow of colors. Red and greens are known to represent charged atomic oxygen, whereas blues and purples denote molecular nitrogen, according to NASA.

NASA's Curiosity rover was also able to record the sunset on the Martian surface when it took a photograph of the planet's blue-tinted sky.