Fractional nucleus mass erosion of interstellar comet 2I/2019 Q4 (Borisov) as a function of time with different power-law indices n in the nongravitational force function (discriminated by line styles, see the legend). The corresponding 1σ uncertainty regions, propagated from the formal errors in the nongravitational parameters, are shaded as gray zones. Here we assume κ = 1 for the collimation efficiency coefficient, i.e., perfectly collimated mass loss of the nucleus. The vertical dotted gray line is the perihelion epoch of the comet.