The radius of the Martian orbit around the Sun is about $4$ times the radius of the orbit of Mercury. The Martian year is $687$ Earth days. What is the length of $1$ year on Mercury?

$A$ planet of mass $m$ moves around the sun of mass $M$ in an elliptical orbit. The maximum and minimum distances of the planet from the sun are $r_1$ and $r_2$ respectively. The time period of the planet is proportional to ..........

$A$ planet revolving in an elliptical orbit has:
$(A)$ a constant velocity of revolution.
$(B)$ the least velocity when it is nearest to the sun.
$(C)$ its areal velocity is directly proportional to its velocity.
$(D)$ areal velocity is inversely proportional to its velocity.
$(E)$ a trajectory such that the areal velocity is constant.
Choose the correct answer from the options given below:

$A$ planet is revolving around the sun in an elliptical path as shown in the figure. Which of the following is the correct option?

India's Mangalyaan was sent to Mars by launching it into a transfer orbit $EOM$ around the Sun. It leaves the Earth at $E$ and meets Mars at $M$. If the semi-major axis of Earth's orbit is $a_e = 1.5 \times 10^{11} \, m$ and that of Mars' orbit is $a_m = 2.28 \times 10^{11} \, m$, using Kepler's laws, estimate the time taken for Mangalyaan to reach Mars from Earth in days.

State and prove Kepler's second law (Law of Areas) of planetary motion.