Martian meteorite Teghaza 001 preserves crust at least 4.1 billion years old

Meteorites knocked off Mars by impacts give researchers Martian rock they can analyse in the laboratory. That record has a bias, though. Most Martian meteorites are geologically young, while the planet's surface is dominated by ancient rocks, so the samples on Earth are a poor match for the terrain that orbiters and rovers survey.

In a 2026 paper in Science, Yang Liu and colleagues at the California Institute of Technology, the Jet Propulsion Laboratory and the University of California, Los Angeles describe a meteorite that helps to close that gap. Named Teghaza 001, or Teg 001, it is an igneous rock, one that crystallised from molten material, and it cooled slowly. The authors report that it formed at least 4.1 billion years ago. That figure is a lower limit rather than a precise date.

Teg 001 stands apart from other Martian meteorites in three ways, according to the study: its composition, its mineralogy (the particular minerals it contains) and its texture (how those mineral grains are arranged). The authors determine that it is a sample of Mars' ancient crust, the planet's outer rocky shell.

The rock also points to what lay beneath. The authors trace it to a mantle source, the region of the interior below the crust where the melt originated, that is geochemically distinct and has what they call a primordial composition. In other words, the source appears to have kept a make-up little changed since early in the planet's history.

The meteorite carries a record of water as well. It contains aqueously altered minerals, meaning minerals that were changed by reactions with water. The team measured oxygen isotopes, versions of the oxygen atom that differ in mass, both in the rock as a whole and in individual minerals. Taken together, the authors report, these results show that Teg 001 reacted with fluids enriched in oxygen-18, a heavier and rarer form of oxygen, before an impact ejected it into space.

The study's summary leaves several questions open. It does not state how the age was determined, when the reactions with fluid took place beyond their coming before ejection, or where on Mars the rock originated. And Teg 001 is a single sample. However unusual it is, one rock from an ancient crust cannot by itself show how typical its composition was across early Mars.