Because the orbital period of the Earth is exactly 365.25 days, get Mercury's orbital period by multiplying the figure you just obtained for Mercury by 365.25: Porb ("Mercury") = days. The answer is commensurate with what you would expect from a planet of negligible mass compared to the Earth: about 88 days. As with the other planets, the orbit of Mercury is not perfectly circular but rather elliptical, with its major axis pointing almost directly towards the Sun. The eccentricity of Mercury's orbit varies between 0.09 and 0.13 over an orbit of about 87.9 days. That means that if Mercury were located at a point on its orbit where the distance from the Earth was equal to its average distance from the Earth (about 59 million km), then it would experience extreme temperatures: close to 500°C near the Sun and -180°C near the Earth. The reason why Mercury has such extreme temperatures is because it orbits so close to the Sun. If Mercury were as far away as the Earth then it would experience temperatures similar to those on Earth, since it is only the proximity to the Sun that makes the difference. It takes Mercury approximately 24 hours to complete one orbit around the Sun.