Sunsets On Mars Are Blue

On Earth, the sky is blue during the day and turns orange and yellow at sunset. On Mars, the exact reverse is happening. The "Red Planet" of Mars has a reddish-orange midday sky and a blue evening sky.

Only 1% of Earth's atmospheric pressure exists on Mars, where the "air" is composed of carbon dioxide and iron-rich dust, which scatters low-frequency red light and gives the sky its reddish hue. The Curiosity, Spirit, and Opportunity rovers have captured images of the blue sunset light that is visible when the red light is scattered away from the line of sight during sunsets on Mars.

According to Mark Lemmon of Texas A&M University, College Station, a member of the Curiosity rover mission's science team, "the colors arise from the fact that the very fine dust is the correct size so that blue light penetrates the atmosphere slightly more efficiently." "Blue light stays nearer to the Sun's direction than other colors of light do when it reflects off the dust. The rest of the sky is yellow to orange because red and yellow light scatters throughout the atmosphere rather than being absorbed or remaining near the Sun."