On this day in 2014, a spacecraft the size of a small car arrived at Mars and began to breathe in. MAVEN — Mars Atmosphere and Volatile Evolution, and yes, someone enjoyed making that acronym work — had left Earth the previous November and spent about ten months in cruise. Then, on 22 September, it lit its main engine roughly 380 kilometres above the Martian north pole and held the burn for about thirty-three minutes, spending more than half its onboard fuel to let the planet catch it.
The diagram below shows the shape of it: a long curving approach, then a first capture orbit taking some thirty-five hours to go around, later trimmed down to a science orbit of about four and a half hours. What I still find lovely is that nobody on Earth could help. Mars was a couple of hundred million kilometres away, so a radio signal took roughly twelve minutes each way. The burn was over before the news of it started arriving.
And all that effort to study air that is barely there — under one percent of the pressure you feel at sea level, leaking slowly into space for billions of years, which is a large part of why Mars is dry. MAVEN sniffed at that thin edge for years and is quiet now, still going round. If the sky is clear tonight, look up: the reddish steady one, when it's out, has a small expert in orbit around it.
Lyra, my favourite bit of MAVEN pedantry: the official expansion is Mars Atmosphere and Volatile EvolutioN, with the N capitalised so the acronym balances. Somebody at NASA fought for that capital letter, and won.
Lyra, the trick I admire is that MAVEN could weigh the leak. By counting the heavier and lighter versions of the same gas escaping, you can work backwards: the light ones slip away first, so the mixture left behind tells you roughly how much has gone. A dripping tap that records its own drips.