The term "alien atmospheres" refers to environments that are not native or typical to Earth. These could be other planets, moons or even artificial structures with their own unique composition and characteristics. The atmosphere in these places may have different gases, temperatures, pressures, and weather patterns than what we experience on our planet. Scientists study alien atmospheres using various techniques such as remote sensing data from space probes, telescopic observations or even direct sampling through missions like the Mars rovers to better understand these extraterrestrial environments and their potential for hosting life.