Asteroid 3753 Cruithne

3753 Cruithne is an asteroid that has an orbital period of 364 days and a semi-major axis of 0.998 AU, very similar to Earth. Therefore, it has a 1:1 resonance with the Earth, even though it does not orbit the Earth - Cruithne is NOT a moon of Earth. 

Globedia (note: this website is in Spanish)

 



But unlike Earth, its orbit is much more eccentric with a perihelion of only 0.484 AU (between the orbits of Mercury and Venus) and an aphelio of 1.51 AU (at the orbit of Mars). As shown in the next graphic, it has a normal, elliptical orbit.



"Orbits of Cruithne and Earth". Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons -

However, when you compare the orbit of Cruithne with a stationary Earth, the orbit takes on a strange shape - it has a kidney bean shape relative to Earth. Again, this does not mean that it orbits the Earth and is another moon of Earth. What the kidney bean shape reveals is how the position of 3753 Cruithne compares to the Earth.

"Horseshoe orbit of Cruithne from the perspective of Earth". Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons -

 

Next time, I'll be posting about an even stranger orbital path relative to Earth - a horseshoe shape.