Question 1009: Follow that planet!

X is an asteroid which is in normal elliptic orbit the Sun. Its period of revolution around the Sun, approximately 364 days at present, is almost equal to that of the Earth. Because of this, X and Earth appear to "follow" each other in their paths around the Sun. This is why X is sometimes incorrectly called "Earth's second moon". X's distance from the Sun and orbital speed vary a lot more than the Earth's, so from the Earth's point of view X actually follows a kidney bean-shaped horseshoe orbit ahead of the Earth, taking slightly less than one year to complete a circuit of the "bean".



ID X

Answer: The asteroid 3753 Cruithne