Fiery rose and peach sunset skies are a unique advantage of our home on Earth. But what colors appear when the sun sets on other planets in the solar system?
The answer depends on the planet. On Mars the sun comes and goes with a blue glow. According to NASA, the sunset sky on Uranus changes from blue to turquoise. And on Titan, one of Saturn’s moons, the sky changes from yellow to orange to brown while the sun falls below the horizon.
Sunset colors are not uniform because these hues are largely a product of the atmosphere of every planet and how the particles they contain scatter sunlight, said Kurt Ehler, a professor of mathematics at Truckee Community College in Reno, Nevada, and lead author of a paper by 201
Connected: Do other planets have eclipses?
“It’s difficult,” Ehler told Live Science. “Everyone had a preconceived notion that the mechanism [for sunsets] is a replica of what we see on earth. “But that is not the case.
On Earth, the atmosphere consists of tiny gas molecules, mainly nitrogen and oxygen, which are more effective when scattered – that is, when absorbed and re-emitted in a different direction – short-wave light such as blue and violet than longer red wavelengths. The selective type of scattering caused by small molecules is called Rayleigh scattering. There is one blue sky At noon, but at sunset and sunrise, when the sunlight has to move on, more blue light is scattered away. It is the longer red and yellow wavelengths that reach our line of sight and produce the vibrant shades of red that we see.
Any planet whose atmosphere is dominated by gas will follow a similar pattern of longer-wave colors that become more dominant at sunset, Ehler said. For example, on Uranus, the gas particles of hydrogen, helium and methane scatter the shorter blue and green wavelengths in its atmosphere, while according to NASA they absorb longer red wavelengths (but for the most part do not re-emit). This creates a bright blue sky that turns turquoise at sunset when blue light is scattered relative to the longer greenish wavelengths.
If the atmosphere of a planet is dominated by something other than gases, everything about how the sunset appears will be different. Take the blue Mars sunset. “The density of the atmospheric gas is only about 1/80 of what it is here,” said Ehler about Mars. “The scatter is dominated by larger dust particles.”
In a 2014 study using data from the Mars Rover Spirit, Ehler and his colleagues found that Martian dust scatters light very differently than gas molecules. “The reason for [the] blue sunset is the pattern in which light is scattered by them [dust] Particles, “he said.
Like molecules here on Earth, gas molecules scatter light in all directions. In contrast, dust mainly scatters the light in one direction – the forward direction, Ehler said. In addition, dust particles scatter red light at much larger angles than blue light. Since the blue light is not scattered very far, it becomes more concentrated, so that “the blue light is about six times as intense as the red light” on Mars, Ehler said.
Connected: How much would you weigh on other planets?
When you look at the sunset on Mars, you actually see that “the sun disk is white because the light does not change color when it passes through the Martian atmosphere,” said Ehler. “There is a bluish glow around the sun. And further out, the sky looks reddish. There you see red lights that are scattered at larger angles.”
As for the other planets and moons, it is almost impossible to predict what the sunset will be like without a thorough understanding of its atmospheric composition. If these celestial bodies have a gaseous atmosphere, you would expect to see longer wavelengths of light at sunset, Ehler said.
“Where [the] The atmosphere is dominated by other substances, I cannot tell you, “said Ehler. Different types and size distributions of dust scatter the light in a unique way. In other words, if you think a sunset on earth is” out of this world , “Think again – it really is an exclusive feature specifically for planets with a gaseous atmosphere.
Originally published on Live Science.