Air and People
What the Exodus set out for in the first place: a world where a person steps out of the airlock without a pressure suit. A probe measures the air in its first minute of flight, and the game tells you plainly what you would have to wear.
Why measure the air
The Exodus was flying to a planet where a person could live. Your copy stopped being a person long ago, but the question stayed, and every planet and moon on the "Object" screen has a "Habitability" button. It tells you what a person would have to wear to step outside.
To answer, you need to know what there is to breathe. The flag "has an atmosphere" only says that something hangs above the ground.
A minute over the world
The air is measured by the probe. You don't have to do anything for it: the first minute of flight over a world whose air nobody has measured yet is the analysis. A bar runs on the "Atmosphere" panel on the right, and when it fills, the main gases and the answer appear there. Either a ship or your own station over that world can send the probe.
Crash the probe or leave the flight early, and the minute is lost: the next probe starts from zero. Over a vacuum there is nothing to measure, and the answer is there at once.
Measured air is a fact of the world. Whoever arrives second sees the composition at once and doesn't have to spend a minute over that world.
What is in the air
The composition follows from the world itself: from its warmth, its gravity, its water and whatever grows on it. A cold world keeps some gases in its sky, a hot one others, and a gas giant has a mix of its own. Free oxygen doesn't linger in the air by itself: somebody has to breathe it out.
The ladder of protection
The answer is one rung of six: no protection, mask, suit, pressure suit, dome, uninhabitable. Below it stand five gauges: pressure, oxygen, poisons, ground temperature and gravity. The worst of them picks the rung: a world with splendid air and frost off the scale still calls for a pressure suit.
Each gauge shows the band "where no protection is needed" and the world's mark. You can see both how much was missing and what exactly.
What the instrument doesn't know
Over a living world there is the line "biology — unknown". Whether you can breathe, the instrument will say; what alien life would do to a person, it won't. That is the honest limit of any measurement, and the game doesn't hide it.
What the answer gives you
Nothing but knowledge: the rung opens no orders and costs nothing. But it answers the very question the whole expedition started with. Worlds where you can step out in ordinary clothes are few, and whoever finds one will be the first to know.