A new picture of Earth’s ‘mini moon’

For centuries, people believed that the Moon was Earth’s only natural satellite. While this remains true for permanent moons, such as ours, astronomers have discovered in recent years that Earth occasionally acquires tiny temporary companions known as mini moons. These small asteroids are briefly captured by Earth's gravity, orbit the planet for a limited time, and eventually escape back into orbit around the Sun.

I have written other articles featuring mini-moons, but last week, China captured images of an asteroid, which has also been referred to as a mini moon, that has been orbiting Earth. The spacecraft known as Tianwen-2 photographed the object and was ultimately designed to collect and return samples of this object to Earth for scientific study. According to an article by Scientific American, the object is called Kamo’oalewa and orbits our planet as close as 9 million miles and is far away as approximately 25 million miles.

Mini moons should not be confused with quasi-moons, which are sometimes incorrectly described as Earth's second moon. A quasi-moon follows an orbit around the Sun rather than around Earth but remains near our planet for long periods because its orbit is synchronized with our planet’s orbit.

A mini moon is a small asteroid that becomes temporarily trapped by Earth's gravitational pull. Unlike Earth's Moon, which has orbited our planet for billions of years, a mini moon remains in orbit for only a few weeks, months, or, in rare cases, several years. Most mini moons are only a few feet to several miles in diameter, making them extremely faint and difficult to observe with even powerful telescopes.

Although the asteroid appears to circle Earth from our perspective, it is never actually captured by Earth's gravity and therefore is not a true moon. Scientists suspect that Kamoʻoalewa may not be an ordinary asteroid. Spectral observations indicate that it may resemble lunar rocks, leading to the intriguing possibility that it is a fragment blasted off Earth's Moon by a large impact millions of years ago. If samples confirm this hypothesis, it will represent the first known asteroid that originated from the Moon.

Launched on May 28, 2025, China’s Tianwen-2 has been traveling to Kamo’oalewa, a journey that has spanned over 620 million miles. The rock is about 66 feet in diameter, and it rotates on its axis every 28 minutes. It was discovered in 2016, and Tianwen-2 was launched to retrieve samples.

Tianwen-2’s equipment will allow it to recover samples from the asteroid in three ways. One is to use a “touch-and-go” method, or an “anchor-and-attach” method where the spacecraft will physically attach itself to the space rock and then start collecting samples of the surface and subsurface. It could also use a “hovering” method as a robotic arm will deploy from the spacecraft as it hovers above the asteroid and scoop up some of the surface material.

Once the samples from the asteroid are obtained, they are expected to be transported to Earth around late 2027, where scientists will study them in laboratories using more sophisticated instruments for analysis. After releasing its Earth return capsule, the spacecraft will use Earth's gravity to redirect itself toward the main-belt comet 311P/PanSTARRS and projected to rendezvous with it in January 2035. During its mission, Tianwen-2 is expected to investigate why some objects in the asteroid belt occasionally produce tails of dust like comets. Scientists hope these observations will improve understanding of how water, ice, and other volatile materials are distributed throughout the solar system.

If Tianwen-2 confirms that Kamoʻoalewa originated from the Moon, it would provide scientists with a unique sample of lunar material launched naturally into space by an ancient impact. Such a discovery would improve understanding of the Moon's geological history and the violent collisions that shaped the early Earth-Moon system.

However, if Kamoʻoalewa proves to be an ordinary asteroid, the mission will still provide invaluable information about the composition of near-Earth objects and the processes that formed the solar system more than 4.5 billion years ago.

In terms of our local weather, the very dry weather pattern continues across the Inland Northwest. For 2026, total precipitation at Cliff Harris’s station in Coeur d’Alene has been 9.01 inches compared to a normal of about 14.30 inches. Other locations around Coeur d’Alene have received over 10 inches of moisture for the year. Although this total is about 63% of normal, it’s still higher than last year’s figure to date of 8.26 inches.

Unless there is an isolated afternoon or evening thunderstorm, very little, if any, rainfall is expected through the end of next week, probably later. As I’ve mentioned earlier, it’s also possible that we could see an increase of moisture from south later in August or September due to a stronger sub-tropical jet stream. The moisture will be needed as over 70% of the western U.S. is in drought.

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Contact Randy Mann at [email protected].