Cruithne: Earth’s Second Moon

Key Takeaways

  • Cruithne is a small asteroid that orbits the Sun and is often referred to as “Earth’s second moon.”
  • It was discovered in 1986 and is one of the few co-orbital objects ever discovered.
  • Cruithne’s low escape velocity means that one could potentially jump off the asteroid and float in space.


Cruithne, also known as 3753 Cruithne, is a small asteroid that has captured the fascination of astronomers and space enthusiasts alike. While it is often referred to as “Earth’s second moon,” it is important to clarify that Cruithne does not actually orbit the Earth. In this article, we will explore the intriguing characteristics of Cruithne, its discovery, and its relationship with Earth.

Discovery of Cruithne

Cruithne was discovered on October 10, 1986, by Duncan Waldron, an astronomer at the University of Arizona. Its name, Cruithne, is derived from the ancient Pictish people of Scotland, who were known for their astronomical observations. The discovery of Cruithne was significant as it was one of the first co-orbital objects ever found. Co-orbital objects are celestial bodies that share the same orbit around the Sun as another object, in this case, Earth.

The Unique Orbit of Cruithne

Cruithne’s orbit is what makes it particularly fascinating. While it does not orbit the Earth, its path around the Sun is such that it appears to have a horseshoe-shaped orbit relative to Earth. This means that from Earth’s perspective, Cruithne seems to move forward and backward in the sky over a long period of time. This peculiar orbit is a result of the gravitational interaction between Cruithne, Earth, and the Sun.

A Day on Cruithne

If one were to stand on the surface of Cruithne, they would experience a rather uneventful day. The asteroid’s rotation period is approximately 27 hours, which is slightly longer than a day on Earth. However, due to its small size and lack of significant geological features, there would not be much to see or explore. The surface of Cruithne is mostly covered in rocks and craters, similar to many other asteroids in our solar system.

Escape Velocity and Space Exploration

One interesting aspect of Cruithne is its low escape velocity. Escape velocity refers to the minimum speed an object needs to achieve in order to escape the gravitational pull of a celestial body. Cruithne’s low escape velocity means that if one were to jump off the asteroid’s surface, they would not be pulled back by its gravity and could potentially float in space. However, it is important to note that this would be a dangerous and ill-advised endeavor, as the lack of gravity and atmosphere in space poses significant risks to human life.

Scientific Research and Exploration Opportunities

Despite its relatively small size and distance from Earth, Cruithne has attracted the attention of scientists and researchers. Its unique orbit and co-orbital relationship with Earth provide valuable insights into the dynamics of celestial bodies in our solar system. Studying Cruithne can help scientists better understand the gravitational interactions between objects and refine our understanding of orbital mechanics. Additionally, the exploration of Cruithne could potentially serve as a testing ground for future space missions and technologies.


Cruithne, the small asteroid often referred to as “Earth’s second moon,” offers a fascinating glimpse into the complexities of our solar system. While it does not actually orbit the Earth, its horseshoe-shaped orbit relative to our planet has captured the imagination of astronomers and space enthusiasts. With its unique characteristics and potential for scientific research, Cruithne serves as a reminder of the vastness and intricacies of the universe we inhabit.

Written by Martin Cole

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