Kepler solar system explorer

A central mass at the origin, four inner Solar System planets at their real semi-major axes and eccentricities (Mercury through Mars), plus a fifth user- controllable test orbit. All five bodies obey the same inverse-square law in $GM = 1$ units where $a = 1$ corresponds to Earth's orbit (1 yr). The inset shows Kepler's third law: every body lands on the dashed $\log(T^2) = \log(a^3)$ line, regardless of eccentricity. Adjust the test orbit's $(a, e)$ and time-speed; the test point's location on the inset moves with the slider.