Earth’s quasi-moon Kamo’oalewa is not made of cheese
That our planet has a moon is generally accepted, though one popular conception of its composition is doubtful. What isn’t so well known is that Terra has a number of quasi-moons: small objects that remain close to the plant while they orbit the sun. Despite being nearby, quasi-moons are difficult to observe, and so little is known about their origin or composition.
One such Terran quasi-moon is Kamo’oalewa, an asteroid whose orbit transitions between quasi-satellite and horseshoe orbital states. The name Kamo’oalewa derives from a Hawaiian word referring to an oscillating celestial object.
Given its orbit, it is thought that Kamo’oalewa originated in the Terra-Moon system as a fragment of the Moon, possibly as ejected debris from a meteor impact on its surface, or otherwise the gravitational breakup of a larger body during a close encounter. Thanks to Tucson-based planetary astronomer Benjamin Sharkey and others using the Large Binocular Telescope and Lowell Discovery Telescope in Arizona, we now learn that Kamo’oalewa has a red reflectance spectrum very similar to that of minerals on the Moon’s surface.
Sharkey and his colleagues show that the spectrum of Kamo’oalewa suggests a silicate composition, but with a reddening beyond that usual for asteroids in the inner solar system. The best compositional match is with lunar silicates.
The latest finding does not, however, confirm the lunar origin hypothesis. Kamo’oalewa could, for example, come from an as-yet undiscovered quasi-stable population of Terra’s so-called Trojan asteroids orbiting near the L4 and L5 Lagrange points between planet and sun.