The NASA Mars rover "Perseverance" has captured a strange and rare "blue sunset" over the horizon of the Red Planet. The American space agency noted that the spacecraft obtained the image on its 842nd Martian day, on July 4, using its navigation camera located on top of the vehicle's mast that assists with driving.
As the red sky began to turn darker, the adventurous robot turned its left navigation camera towards the hazy horizon. In a single shot, it captured the stunning sunset, where the sky of the Red Planet glowed in a beautifully cool and strange blue color. The image from "Perseverance" shows the sunset on the Martian horizon glowing in a cool and strange bluish-green hue. This image sheds more light on the physics behind the bizarre sunset, the physics of light scattering on the Red Planet, and how it contrasts with a similar phenomenon on Earth.
On Earth, when different wavelengths of sunlight enter the atmosphere, they scatter by small particles including gases like oxygen, nitrogen, carbon dioxide, and water vapor, along with other particles. During peak daytime, when the side of the planet is closer to the sun, blue light – which travels in shorter waves – scatters away widely, making the sky appear blue during this time. However, during sunrise and sunset, sunlight travels a longer distance in the atmosphere. This leads to the scattering of shorter wavelength light, including purple and blue, leaving only orange and red light to reach the eyes.
Mars's atmosphere is known to be extremely thin (about 1% of Earth's atmosphere), and the Red Planet is also 50% farther from the sun than Earth. Sunlight interacts with large iron-rich dust particles on the Martian surface, compared to oxygen, nitrogen, and carbon dioxide on Earth. This dust scatters the low-frequency red light during the day, giving Mars its distinctive red sky. At sunset, when the light has a longer distance to travel, the red light dissipates, painting the sky in a cool blue color.
