Meteorite Amgala 001 – Western Sahara

Amgala 001 is a meteorite that was found in December 2022 in the area of Saguia el Hamra, Western Sahara, near the town of Meharrize. Thetotal mass of the fragments found is approximately 35 kilograms, with the largest piece found weighing 5.2 kilograms.

Origin

The Amgala 001 meteorite was brought to Earth after a powerful impact that blasted rocks from the surface of Mars into space. This process begins when an asteroid or comet hits the surface of Mars with enough energy to cause a massive explosion. Such an impact creates a crater and releases a large amount of energy that rips apart the surface rocks and shoots them into space.

These ejected fragments, which are now outside Mars' gravity, move through space like meteoroids. If their trajectory crosses Earth's orbit, they can be captured by Earth's gravity and enter the atmosphere as meteors. If they survive their passage through the atmosphere and hit the Earth's surface, they become meteorites.

Characteristics

Amgala 001 has a weathered brown surface with a bumpy appearance, while the interior is greenish grey with visible darker olivine phenocrysts and is characterised by a high degree of shock metamorphosis and a low degree of weathering. Its chemical composition and the isotopic composition of the gases inside are very similar to those of the Martian atmosphere, as confirmed by measurements from the Viking missions to Mars.

Classification

This meteorite is classified as a Shergottite, a type of meteorite originating from Mars. About three-quarters of all Martian meteorites are classified as shergottites. These meteorites get their name from the Shergotty meteorite that landed in Sherghati, India in 1865. Shergottites are igneous rocks with mafic to ultramafic lithology.

Mafic rocks are characterized by high magnesium and iron content and contain dark minerals such as pyroxenes, olivines and amphiboles. These rocks are usually dark in colour, which is due to their high iron and magnesium content. Typical examples of mafic rocks are basalts, or basalts, and gabbro.

Ultramafic rocks are even higher in magnesium and iron than mafic rocks and contain very little silicon. These rocks are extremely dark to black because they contain a high proportion of dark minerals such as olivine and pyroxene. Peridotites and dunites, also known as olivinites, are common examples of ultramafic rocks.

Both of these categories of rocks are mostly formed in areas of the Earth's mantle and lower crust where partial melting and differentiation of magma occurs. The study of these rocks provides valuable information on the composition and processes involved in the Earth's mantle and in the formation of igneous rocks. Due to their specific composition and structure, shergottites are a key material for understanding geological processes not only on Earth but also on Mars.

Age

Shergottites crystallised around 180 million years ago. This relatively young age is surprising given that most of the Martian surface appears to be much older. Moreover, it is also surprising given the smaller size of Mars, which would suggest faster cooling and older surface formations.

This discrepancy between expected and actual ages is known as the "shergottite age paradox." Some scientists believe that these meteorites may actually be much older than current dating methods are able to detect. This paradox remains unresolved and is the subject of active research and debate among scientists.