FIELDS detected the natural, low-frequency radio waves as the probe moved through the Venusian atmosphere; the radio data, subsequently, has allowed scientists to calculate the thickness of the planet’s electrically charged upper atmosphere.

NASA scientists, who published their findings in the journal Geophysical Research Letters, say this latest detection shows that Venus’ upper atmosphere—or its ionosphere—is indeed thinning.

This thinning, the scientists say, is happening in accordance with the Sun going through its “solar minimum” period; that is, the period of its 11-year-long surface activity cycle in which it has the fewest sunspots.