import numpy as npimport matplotlibpyplot as plt# Constants SI unitsG = 66743e-11 # gravitational constantm_s = 19885e30 # mass of Sunm_m = 7342e22 # mass of Moonm_mer = 3301e23 # mass of

The error "invalid index to scalar variable" occurs because the variable r0_mer is defined as a scalar value instead of an array.

To fix the error, we need to change the definition of r0_mer from a scalar value to an array.

Replace this line:

r0_mer = 2.44e6    # radius of Mercury

with this line:

r0_mer = np.array([2.44e6, 0])    # radius of Mercury

This will create a 2D array for the initial position of Mercury, with the x-coordinate being 2.44e6 and the y-coordinate being 0