Solution (source code)

= Solution

<Kepler's third law> for negligible planet <mass> gives $a_P/a_E=(P_P/P_E)^{2/3}$. Therefore $a_P=1.5\times10^8(248)^{2/3}\simeq5.92\times10^9\,\mathrm{km}$. The furthest point is <apoapsis>, so
$$
\boxed{r_{\max}=a_P(1+e)\simeq7.40\times10^9\,\mathrm{km}.}
$$
The supplied orbital period and <eccentricity> are sufficient; no present-day ephemeris is needed.