What colors are the planets of our solar system? And why are they so different?

The planets of the solar system are varied in their appearance. Mercury is slate gray while Venus is pearly white, Earth a vibrant blue and Mars a dark red. Even the gas giants are different, Neptune and Uranus opaque blue, while Jupiter and Saturn are mostly beige with bright red-brown belts. But why are these planets so different?

It starts at the beginning

It turns out that the stars and their planets form at the same time from a disk of gas and dust called a solar nebula. Most of the gas – mostly hydrogen and helium – was swallowed by our young star; no surprise given that the Sun contains between 99.8 and 99.9% of the total mass of the solar system.

At the same time, debris mixed with the nebula collided again and again, eventually accumulating into planetesimals and then protoplanets. Jupiter, Saturn, and even Neptune and Uranus were able to pull some of the nebula’s hydrogen and helium to swaddle their cores, causing them to grow to truly massive sizes.

Closer to the Sun, the heat was so intense that it vaporized anything that did not have a high melting point; only rocks remained. Iron, sulfur, aluminum, nickel and other metallic compounds circled the baby Sun for millions of years, colliding with each other, eventually coalescing into the inner planets. But these young planets were unable to attract as much gas to themselves as their larger sisters. Whatever they managed to do, they are unlikely to have lasted. Instead, the inner planets relied on liquids and gases collected during impacts and volcanic outgassing to form the atmospheres we see today.

All this to say that the first building blocks of each planet contribute to our colorful planetary array. But what exactly is on each planet in the solar system that determines its unique appearance?

A wild color system

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