Maximum eccentricities reached by a Kepler-10b-like planet after 10⁶ yr, for different initial semimajor axes. We place planet b with a high initial eccentricity (e₁ = 0.5, purple horizontal line at 0.75) and inclination (i₁ = 28.°6), to artificially speed up the diffusion to large e₁. The outer planets have eccentricities and inclinations drawn from a Rayleigh distribution with ﹩{\sigma }_{e}={\sigma }_{i}=0.1﹩ (rms values of 0.14) and have the same spacing and masses as in Figure 5. The remaining orbital elements (f, ω, Ω) are drawn randomly. The integrations include relativistic precession and nondissipative tidal bulges, and we indicate the maximum eccentricities allowed by relativistic precession (Equation (11)) and tidal bulges (Equation (14)). For reference, we indicate the threshold to become a USP planet of ﹩{a}_{1}(1-{e}_{1}^{2})\lt 0.02\,\mathrm{au}﹩. The integration timestep is 0.1 day.