A small object, presumed to be a tiny asteroid, has been discovered in a distant orbit about the Earth, a highly unusual circumstance, since asteroids normally orbit the Sun. The new “mini-moon” has been given the asteroid designation 2020 CD3, but in view of its strange orbit, there is a chance that the object is an old lunar spacecraft or a small discarded rocket stage. Based on its brightness, 2020 CD3 is very small, no more than 1 to 2 meters (3 to 6 feet) in size. The discovery was made on February 15, 2020 by the NASA-funded Catalina Sky Survey, one of the most productive asteroid-searching programs currently in operation. Trajectory analyses indicate that 2020 CD3 has been orbiting Earth for at least a year and probably more, presumably after being captured by the Earth’s gravity from an orbit about the Sun. During its time near our planet, the object has completed at least three large looping orbits with periods of between 70 and 90 days. At the farthest point in these orbits, the object is about four times as far away as the Moon. Its final close approach to the Earth occurred on February 13th at a distance of about 41,000 km (25,000 miles) from Earth’s surface, above the height of the geosynchronous ring of satellites at 36,000 km (22,000 miles). It is currently about 110,000 km (68,000 miles) from the Earth, and now moving away just fast enough that it will escape the Earth’s gravitational influence in early March and return to an orbit about the Sun.
The trajectory of 2020 CD3 prior to June 2019 is highly uncertain. However, future observations over the next few weeks should help refine the orbit of 2020 CD3, confirm or further rule out the possibility of it being space junk, and allow for better characterization of its physical properties.
2020 CD3 is not the first apparent mini-moon. Back in 2006, a somewhat larger asteroid called 2006 RH120 was also found in a temporary orbit about the Earth. That object was captured in mid-2006, made a series of distant loops about our planet, and departed in mid-2007.