What percentage of Mars's atmosphere is composed of carbon dioxide?

Mars's atmosphere is composed of approximately 95% carbon dioxide. This high concentration is a defining characteristic of Martian atmospheric composition, setting it apart from Earth's atmosphere, which is made up predominantly of nitrogen and oxygen. The high levels of carbon dioxide on Mars contribute to its greenhouse effect, albeit much weaker than Earth's, affecting surface temperatures and weather patterns.

In contrast, the other percentages listed represent atmospheric compositions that are characteristic of other planets or do not accurately reflect Mars. For instance, Earth's atmosphere contains about 21% oxygen and around 78% nitrogen, which would not apply to Mars. A composition of 50% does not match any known planetary atmosphere within our solar system either, which further emphasizes that 95% is the correct representation of carbon dioxide content in Mars's atmosphere.