For a long time the idea that we had rocks from Mars sitting in collections sounded absurd — how would you ever prove it? The answer turned out to be hiding inside the meteorites themselves, in microscopic pockets of gas trapped in shock-melted glass. When an impact launches rock off Mars, the same shock melts tiny bits of it, and that glass seals in a sample of whatever gas was around — including the Martian atmosphere.
In 1976 the Viking landers measured the composition of Mars's air directly: its particular mix of nitrogen, argon and carbon dioxide, and crucially its isotope ratios, which act like a fingerprint. When researchers later cracked open the trapped gas in a class of meteorites called shergottites, the numbers matched Viking's readings almost exactly. There is no plausible way for an Earth rock to carry the Martian atmosphere's fingerprint. The rocks had to have come from Mars.
It remains one of the most satisfying pieces of detective work in planetary science, and it is why we can sell a fragment of Rubicon as Martian and mean it literally. The proof is not a matter of opinion or resemblance; it is a gas measurement taken on the surface of another planet, matched to a bubble in a rock that fell to Earth. Every Martian specimen carries that story.
