Earth's stratosphere is above Earth's protective atmosphere, having conditions that are dry and cold, have intense ultraviolet solar radiation, and vacuum-like air pressure. These factors make the stratosphere a great stand-in for the surface of Mars. Why would scientists want to introduce bacteria into Earth's stratosphere?

What a great way to see how bacteria exposed to Martian-like conditions will survive. By testing how well these bacteria do in the stratosphere we can gain insight into several things. 1) the likelihood that any bacteria still survives on Mars 2) how well bacteria introduced to Mars could survive and if there are existential risks to doing so and 3) how bacteria introduced to harsh conditions react more broadly, even on earth.