Planetary Atmospheres

Ten worlds in our solar system carry a substantial atmosphere, and humanity has measured every one of them — by dropping probes into four, landing weather stations on one, and flying radio signals through the rest. Each of the ten gets one slot: the measured pressure, temperature, composition, and the missions that did the measuring. From Venus's crushing 92 bars at 737 K to Triton's whisper of nitrogen at 38 K above frozen geysers — a span of nearly seven million times in pressure, all of it measured.

The dex

One slot = one solar-system body with a global atmosphere at a measured pressure of at least 10 microbars: Venus, Earth, Mars, Jupiter, Saturn, Titan, Uranus, Neptune, Triton, and Pluto. That threshold is frozen — the roster grows only if a new atmosphere is actually measured somewhere, never by loosening the rule. Five of the ten have been measured from inside: Venera 4 fell through Venus's clouds in 1967, Viking landed a barometer on Mars in 1976, the Galileo probe rode into Jupiter in 1995, Huygens parachuted through Titan in 2005, and Cassini ended its life sampling Saturn's atmosphere directly in 2017.

Provenance

Slot values come from the NASA NSSDC Planetary Fact Sheets — NASA's canonical compilation of measured planetary values — and, for the moons, straight from the mission results: the Huygens descent profile for Titan and the Voyager 2 occultation for Triton. Every slot names its measuring missions.

What's in a slot

• Identity — body name, type (planet, moon, dwarf planet), and what it orbits
• The atmosphere — surface pressure and temperature (for the gas giants, which have no surface, values at the standard 1-bar reference level), scale height, and mean molecular weight
• Composition — the measured gas mix by volume, with the dominant gas called out
• The record — which missions measured it, and the first spacecraft to measure it from inside, where one has

What you will not find: model atmospheres. Global-circulation-model output and "reference atmosphere" fits are simulations, and the dex holds measured reality only. Where a published value is a range, the slot carries the range — not an invented midpoint.