Two planets are rotating around a star in elliptical orbits. The orbit of planet $1$ has semi$-$major axis a$1=0\mathrm{.}29$ astronomical units $($AU$).$ Its period is T$1=6\mathrm{.}7$ years. The orbit of planet $2$ has semi$-$major axis a$2=0\mathrm{.}66$ AU$.$ Express the period of planet $2,$ T$2,$ in terms of T$1,$ a$1$ and a$2.$