Create a grid using the function meshgrid (x, y), where x and y are coordinates of points in the solar system. Name this grid as grid_mat. By choosing the origin of the grid to be the Earth, specify the coordinates of Moon and Mars. Make sure that the Moon is between Earth and Mars. Assume the orbits of Moon and Mars to be circular.
grid_mat = sqrt((X-a).^2 + (Y-b).^2) ;