Scientists have discovered a reservoir of liquid water on Mars - deep in the rocky outer crust of the planet.
The findings come from a new analysis of data from Nasa’s Mars Insight Lander, which touched down on the planet back in 2018.
The lander carried a seismometer, which recorded four years’ of vibrations - Mars quakes - from deep inside the Red Planet.
Analysing those quakes - and exactly how the planet moves - revealed “seismic signals” of liquid water.
It’s possible to use it to refer to a non-planet region (bigger or smaller) in a more general sense, but I wouldn’t say that’s the most common usage.