N₂ molecular density for flybys T5, T27, T30, and T87. The top data points, fitted with plain lines, are the averaged molecular density of ¹⁴N ¹⁴N stacked over four data points. The bottom data points, fitted with dashed lines, are for ¹⁴N ¹⁵N molecular density. In blue and red are the fitted lines using equation 3 at high and low altitude, respectively, for ¹⁴N¹⁴N (plain) and ¹⁴N¹⁵N (dashed). The vertical lines are the altitudes below which ¹⁴N¹⁴N (plain) and ¹⁴N¹⁵N (dashed) data point cannot be fitted anymore by the blue curve.