The Big Picture: Sunrise on Mars.

scientificinquirer

February 29

CREDIT: Mathew.vargheese

The phenomenon of sunrise, a daily marvel on Earth, takes on a different character when observed from the surface of Mars. The science behind a Martian sunrise, while fundamentally governed by the same principles that dictate solar appearances on Earth, is nuanced by the distinct atmospheric and environmental conditions of the Red Planet.

Mars, the fourth planet from the Sun, experiences sunrise and sunset much like Earth due to its similar axial tilt of approximately 25 degrees, which is not vastly different from Earth's 23.5 degrees. This tilt is responsible for the seasonal variations on both planets. However, the duration of a day on Mars, known as a sol, is slightly longer, approximately 24 hours and 37 minutes. This means that observers on Mars witness sunrise just a bit later each Earth day if using Earth time to track the passage of time on Mars.

The science behind a Martian sunrise begins with the Sun's light traveling through the Martian atmosphere before reaching the surface. Mars' atmosphere is much thinner than Earth's, composed primarily of carbon dioxide, with traces of nitrogen and argon, and almost 1% of Earth's atmospheric pressure at sea level. This thin atmosphere has a significant impact on the appearance of sunrise on Mars.

One of the most striking differences is the color of the sky during a Martian sunrise. On Earth, the sky near the Sun typically appears reddish at sunrise due to Rayleigh scattering, where molecules in the Earth's atmosphere scatter shorter (blue) wavelengths of light more than longer (red) wavelengths. On Mars, however, the opposite occurs during sunrise. Martian dust, which is more prevalent in the atmosphere and larger than the molecules that cause Rayleigh scattering on Earth, scatters redder wavelengths of light. This scattering by the dust particles in the Martian atmosphere causes the sky around the Sun to appear bluish near the horizon during sunrise, a phenomenon observed by various Mars rovers.

Furthermore, the intensity and clarity of sunlight during a Martian sunrise are affected by periodic dust storms, which can envelop the planet and obscure the Sun. These storms alter the atmospheric conditions, sometimes significantly changing the appearance of sunrise and sunset.