A planet revolves about the sun in an elliptical orbit of semi-major axis $2\times {10}^{12} \mathrm{m}$. The areal velocity of the planet when it is nearest to the sun is $4.4\times {10}^{16} {\mathrm{m}}^2 {\mathrm{s}}^{-1}$. If the least distance between the planet and the sun is $1.8\times {10}^{12} \mathrm{m}$, then the minimum speed of the planet is