A Cosmic Contradiction
On December 3, 1980, a fireball streaked across the sky over what was then South Yemen, ending by carving a small impact pit near a Soviet military base. The single stone recovered, weighing about 2 kilograms, was named the Kaidun meteorite. At first glance, it was a space rock, but analysis revealed a composition so bizarre it challenges our understanding of solar system formation.
Kaidun is a breccia, a rock composed of broken fragments of other rocks cemented together its structure contains a record of the early solar system. It contains clasts, or fragments, of at least three major classes of meteorites that form under wildly different conditions. There are carbonaceous chondrites like CI and CM types, which are containing water-altered minerals and suggest a "wet" origin in the outer asteroid belt. Alongside these are enstatite chondrites (EH and EL types), which are extremely "dry," having formed in the hot, oxygen-poor inner solar system. It also contains fragments of achondrites, materials from differentiated parent bodies that once had crusts and mantles. This collection of mutually exclusive rock types, all fused into one object, makes Kaidun a geological impossibility.
The Phobos Hypothesis
How could such a diverse collection of materials end up in one place? The leading, though still debated, explanation points to Phobos, the larger of Mars's two moons. Phobos is thought to be a captured asteroid or a pile of rubble that coalesced in Mars' orbit. Over billions of years, its surface has been bombarded by impacts from across the solar system.
This constant cosmic peppering would have collected debris from the asteroid belt and even from Mars itself, ejected during major impacts. Proponents of the theory suggest that the fragments collected on Phobos's surface were fused together by the energy of these impacts, creating a composite rock. A later, significant impact could have then blasted a piece of this jumbled surface material off Phobos, sending it on a trajectory to Earth. The presence of two very rare, alkali-rich clasts in Kaidun supports this idea, as they point to a parent body near a large, differentiated planet like Mars.
The meteorite also contains at least 60 different minerals, several of which were new to science when discovered within it. These include florenskyite (FeTiP) and andreyivanovite (FeCrP), phosphide minerals that show complex formation processes in unique space environments. While the Phobos origin remains a hypothesis, the Kaidun meteorite provides a physical sample of materials assembled from across the solar system, a collection unlike any other on Earth.