The phrase "tenuous atmosphere" refers to a situation where there is only a small or weak sense of calm or harmony. It suggests that the atmosphere is fragile and could easily become tense or strained. Full definition
The mission would include a lander spending 35 days on the moon's surface to sample and screen material for traces of life; an orbiter spending three months taking measurements to unravel the basic structure of the planet; and the orbiter crashing into the moon, gathering data on Europa's tenuous atmosphere on the way down. (newscientist.com)
Friction with Mars's tenuous atmosphere slowed the spacecraft as it descended but created temperatures up to 3,800 degrees Fahrenheit. (discovermagazine.com)
Finally, the orbiter would crash into the moon, but would gather and transmit data on the composition of Europa's tenuous atmosphere on the way down, identifying any life - related gases such as carbon dioxide and oxygen. (newscientist.com)