Given that it’s one of humanity’s oldest tools, you might assume we know all there is to know about fire. And sure, we know a lot: As hot air near the base of a flame rises, gravity pulls in colder, denser air to replace it. It’s this cycling of air that provides fresh oxygen and gives flames their characteristic teardrop shapes.
But in a microgravity environment, like the one astronauts experience while in orbit, all bets are off. Here, hot air still expands outward — but it doesn’t move upward, because there is no “upward.” Instead, fires in space are fed only by the random oxygen molecules that stumble into them by chance.
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It’s a process called molecular diffusion, and it produces spherical flames that are different from their Earthly counterparts in more ways than one. Not only do ...
