The eccentricity of an orbit can be calculated using the formula:
eccentricity = (ra - rp) / (ra + rp)
Given that rp = 0.27ra, we can substitute this value in the formula:
eccentricity = (ra - 0.27ra) / (ra + 0.27ra)
eccentricity = (0.73ra) / (1.27ra)
eccentricity ≈ 0.57
Therefore, the correct answer is 0.57.