What does this equation mean?

For the giant planets, only low-degree harmonics are available, and the interpretation problem sharpens. Juno measured Jupiter’s even zonal harmonics $J_{2}$ through $J_{8}$ to high precision, and Wahl and colleagues found that models fit those moments best when the heavy-element core is not compact but dilute, expanded over a significant fraction of the planet’s radius, with total heavy-element content in the core region of roughly 7 to 25 Earth masses [ 17 ] . That range is wide for a reason the authors state plainly: the inferred structure is strongly affected by the chosen hydrogen-helium equation of state [ 17 ] . The gravity data are excellent; the translation into structure is only as good as the laboratory and computational physics behind it.