What is the key diagnostic tool for confirming a planet is terrestrial via data analysis?

Density, which is derived by dividing mass by volume

Confirming whether a distant celestial body is truly terrestrial—meaning its structure is dominated by silicates and metals rather than lighter gases—relies heavily on meticulous data analysis involving two primary measurements: radius (from transit) and mass (from gravitational tug). The crucial step involves calculating the density by dividing the measured mass by the volume derived from the radius. If this calculated density aligns closely with known values for Earth or Mars, scientists can be highly confident that the body possesses the characteristic rocky and metallic composition inherent to terrestrial worlds, moving beyond mere detection to definite classification.