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Start with the full category, then apply the exact boundary: The five layers in NASA’s five-major-layer overview, from the troposphere to the exosphere. Ozone layer and ionosphere are not separate entries in this five-layer list. You only need one qualifying answer. A longer name is not automatically rarer.
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ExosphereExosphere · 90 points · 9 characters
The exosphere is the outermost of NASA’s five main atmospheric layers.
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Exosphere90 points · Shortest accepted spelling: Exosphere
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- Apply the complete question boundary: The five layers in NASA’s five-major-layer overview, from the troposphere to the exosphere. Ozone layer and ionosphere are not separate entries in this five-layer list.
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Each entry belongs to the bounded set defined by the prompt. The named source supports the underlying facts; our editorial scoring is a separate layer.
Source: NASA · Earth’s atmosphere: a multi-layered cake ↗
Reference version: 2026-10-21. See our answer policy for how we handle aliases and omissions.