Asked by David Honey
The colour of a planet is decided by what the surface and atmosphere are made of and how light reflects and interacts with a planet’s atmosphere. Mercury, for example, has virtually no atmosphere, so the grey colour we see comes from light reflected directly from its surface. Jupiter has an atmosphere containing hydrogen and helium, with small amounts of water, ice crystals, ammonia crystals and other elements. These create the clouds of white, orange, brown and red.
While the planets formed at the same time (and planetary formation is a complicated process), lighter elements were blown outward by strong solar winds, allowing each planet to be chemically different from the next.
Answered by Sophie Allan from the National Space Centre
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