The color of the sky on an exoplanet depends on many different factors such as the pressure, density and chemical composition of the exoplanet’s atmosphere.
The presence or absence of dust particles, clouds and vapor, the light coming from the local (parent) star – are also important.
The size of an exoplanet, its composition, color and even its biology (with lifeforms involved), can play an important role.
In other planetary systems, the constellation system in the sky differs much from that of Earth. The more distant the planet from the Sun is located, the less known constellations from Earth’s sky can be seen.
These differences are mainly due to which compounds or gases are scattering and absorbing the sunlight. Scattering is the major factor in most atmospheres and since molecules scatter short wavelengths best, and longer wavelengths the least well, this often results in blue skies. But large amounts of dust can lighten the sky or sometimes make it red.
High-pressure atmospheres would be much lighter than lower pressure ones and could appear completely white or yellow. Considering the large number of factors involved, it isn’t difficult to assume that exoplanet’s sky could be any color at all.
Therefore many colors are possible such as blue, cyan, green, yellow, red, purple, brown, orange or white.
A few years ago, a distant exoplanet GJ 3470b was discovered; it has blue skies but it is unlikely to host life as we know it or any life at all.
On extrasolar planets, the sky can have surprising colors. Perhaps one day we will be able to land on an exoplanet, where instead of blue sky that we’re accustomed to, we can admire a green, red sky or any other color.
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Color of the sky on celestial objects in our Solar System
On Earth, the sky is predominantly blue and becomes orange or red near the setting or rising Sun. Sometimes it is also orange or somewhat red at the time of the sun setting. The sky seen from Mercury and Moon- is black. The sky on Mars – which has much thinner atmosphere (than that of Earth) and the presence of iron oxide-rich dust particles – is rather more of a brown color or red.
On planets where the atmospheric pressure is many times higher than on Earth – white. In the case of high content of methane (Uranus, Neptune), the color of the sky is greenish.