Math Help - Gravitation - Find eccentricity of new orbit?

1. Gravitation - Find eccentricity of new orbit?

A planet is in a circular orbit about a massive star. The star undergoes a spherically symmetric explosion in which one per cent of its mass is suddenly ejected to a distance well beyond that of the planet's orbit. Find the eccentricity of the new orbit of the planet assuming that the planet is unaffected by the explosion.

$e = 0.01$