4.4 billion-year-old meteorite NWA 7533 is straight outta Mars

The meteorite NWA 7533, cut to reveal the interior structure. The light and dark spots are harder rocks (clasts) embedded in a body fused from small grains at high tempertures.

Luc Labenne

No space probe has ever returned a sample from Mars. However, we have had a few Martian rocks delivered to Earth in the form of meteorites, which were dislodged by impacts and set adrift between worlds before crashing here. While studying Mars rocks in situ would be idea, the type of equipment we have on Earth is often impractical to ship aboard spacecraft and land on another planet. In that sense, meteorites provide a complementary way to study Mars, providing data that may be otherwise difficult to obtain.

The latest bit of Mars to undergo study on Earth is meteorite Northwest Africa (NWA) 7533. The chemical abundances and mineral types indicate that it originated on Mars, as it is comparable to rocks analyzed by the Spirit rover. What makes this specimen exciting is its age: radioactive analysis of zircons (silicon compounds containing uranium) revealed that the meteorite is about 4.4 billion years old. That means it formed roughly 100 million years after Mars was born, making it the oldest sample of the red planet yet collected, representative of the earliest period in the planet's history.

Of the thousands of known meteorites on Earth, scientists have confirmed that over 100 originated on Mars. This determination came from a variety of methods, including gasses trapped in the meteorites that have a composition similar to the Martian atmosphere. Additionally, radioactive dating determined that these rocks were much younger than meteorites that originated from asteroids.