The variety of rocks from Mars 🔴

These Martian meteorites document Mars’ history and composition, long before we occupy Mars or engineer a sample return.

Here is my growing collection, with a cm cube at the bottom for scale. These are some of the largest samples, more exotic and rare than pure diamond on Earth.

Starting at top center and going clockwise from 12:

• 12: The 2kg main mass of DaG 1037, a volcanic Martian rock (called shergottite) that looks like the red Mars rocks seen in surface photos. It is even more rare as it contains trapped air bubbles that are a perfect match to the Martian atmosphere measured by the Viking spacecraft. “The composition of this particular specimen includes basalt, cooled lava rich with iron and magnesium, indicating that there was active volcanism on Mars 474 million years ago. The early Martian atmosphere was much thicker, warmer and wetter than it is today, possibly even capable of sustaining life. Most Martian meteorites are believed to be from one asteroid impact/source crater (see 6 and 7 below for rare exceptions). The only way the surface rock could have been ejected into space from the surface of Mars, would be as a result of a huge asteroid impact on the planet’s surface; the energy required to reach escape velocity is so enormous that normal meteorite impacts or volcanic explosions would not provide enough energy release. Such a huge asteroid impact would have had a catastrophic effect on the Martian environment and may be the cause of the loss of the Martian atmosphere and the disappearance of its surface water and possibly life. So, these few meteorites from Mars may provide mute testament to the destruction of the Martian environment and extinction of its life forms." — from: flic.kr/p/Dyq6AX

• 1: Amgala 001, a recent find from 2022, it’s an olivine-phyric shergottite, with a highly textured knobby exterior. The interior is greenish gray in color with darker olivine phenocrysts. The formation ages of meteorites can come from their cosmic-ray exposure (CRE), measured from the nuclear products of interactions of the meteorite in space with energetic cosmic ray particles. This one is particularly young, having crystallized only 180 million years ago, suggesting that volcanic activity was still present on Mars at that time. Volcanic flows are the youngest part of a planet, and this one happened to be hit by a meteor impact, ejecting the youthful Mars. Closeup photos: flic.kr/p/2q3Zobm

• 3: A beautiful green Martian rock — Wan Zawatin 002 — the largest central slice of what we believe to be the largest Poikilitic/Lherzolitic Shergottite ever found. “Lherzolitic shergottites are related to the basaltic shergottites, but their coarse grain sizes mark them as plutonic rocks.” (p.131 of McSween’s Meteorites and Their Parent Bodies) meaning they solidified at great depth on Mars, not from volcanic flows to the surface. Photos: flic.kr/p/2nEw1zF

• 6: The oldest, rarest and most valuable Martian, a whole NWA 7034, nicknamed “Black Beauty” by Dr. Carl Agee, Director of the Institute of Meteoritics, who discovered its marvels: it contains the oldest Martian minerals ever dated (formed 4.48 billion years ago, one of the oldest rocks studied in the history of geology) and it contains ~ 20x more water than any other Martian samples previously encountered (perhaps formed under an early Martian ocean). It was given a new subtype "Martian (polymict breccia)" in the Met Bull. Moreover, in July 2022, it was determined that Black Beauty most likely originated from the Karratha Crater, a relic of the early crustal processes on Mars, and approximately 10 million years ago, the asteroid impact which formed the crater also ejected a large volume of Mars rock into space, some of which perturbed into an Earth-crossing orbit — and it took the long route, a journey of ~15,000 orbits around the Sun before penetrating Earth’s atmosphere. It is a time capsule from early Mars, just 80 million years after the planets started forming! More: flic.kr/p/2oqM8bZ

• 7: A Mighty Green Martian, a 2.4 billion-year-old rock from the early Amazonian period of Mars, the oldest known shergottite. “Analysis of NWA 7635 has helped determine that during its 4.5 billion-year history, Mars had a single volcano that erupted continuously for more than 2 billion years! Mars is known for the most magnificent volcanoes in the Solar System. Olympus Mons is nearly 17 miles high with a footprint the size of Arizona. That’s almost triple the height of Earth’s tallest volcano, Mauna Kea. Martian volcanoes can grow to such enormous proportions because, unlike Earth, Mars doesn’t have plate tectonics that constantly shuffle the surface. So, a volcano, like the one that birthed NWA 7635, can plume for billions of years.” — flic.kr/p/2jjvCLC

• 9: The largest cross-sectional slice of the NWA 7397 main mass. It is a Martian Shergottite (poikilitic), the result of a significant impact on a volcanic magma chamber on Mars. The large salmon-hued oikocrysts (crystals that contain other crystals) are composed of low calcium pyroxene, which enclose crystals of olivine and chromite. flic.kr/p/2iSegSZ

• 11: Greenish-black with a glassy patina, NWA 14269 is an aphyric, diabasic shergottite with melt pockets of ‘swirly’ vesicular glass. The meteorites from Mars exhibit precise elemental and isotopic compositions similar to rocks and atmosphere gases analyzed by spacecraft on Mars, starting with the Viking lander in 1976. Compared to other meteorites, the Martians have younger formation ages, unique oxygen isotopic composition (consistent for Mars and not for Earth), and the presence of aqueous weathering products. flic.kr/p/2mXAG8b

It’s quite moving to hold a piece of Mars in your hands and reflect on its incredible interplanetary journey. A large asteroid impacted Mars long ago and dislodged a rock from the Martian surface with enough energy to escape the atmosphere and gravity well of Mars. Most Martian material remains in roughly a Martian orbit (for most impact angles). But in these examples, the rock orbited the sun for millions of years in an elliptical orbit, and by luck, landed on Earth. Only 0.5% of meteorites are from Mars.

More from McSween’s book Meteorites and Their Parent Bodies, my most recent read on the subject:

Basaltic shergottites “are relatively fine grained and apparently formed as volcanic flows or shallow intrusions on their parent body. Their elongated pyroxene crystals commonly have preferred orientations, probably aligned by magma flow.” (131)

“Shergottite magmas contain at least a small amount of water.” (131)

“Lherzolitic shergottites are related to the basaltic shergottites, but their coarse grain sizes mark them as plutonic rocks.” (131)

“The SNC parent body must be a geologically complex body, characterized by multiple periods of igneous activity. Isotopic data indicate it was differentiated 4.5 billion years ago, and the mantle thus formed had a nonchondritic composition. This source region was remelted approximately 1.3 billion years ago and again more recently to produce shergottite magmas.” (136)

Mg/Si and Al/Si “element ratios illustrate that the peculiar compositions of SNC meteorites are also seen in rocks and soils analyzed by the Viking landers and the Mars Pathfinder rover.” (178)

“Trapped gasses in the EET79001 Antarctic shergottite link the SNC meteorites to Mars. Pockets and veins of shock melt in this meteorite formed by impact, which also implanted atmospheric gasses in the liquid before it solidified as glass. The abundance of carbon dioxide, nitrogen, and various nonradiogenic isotopes of gaseous argon, neon, krypton, and xenon in the glass are identical to those measured in the Martian atmosphere by Viking spacecraft.” (179)

“The ancient highlands of Mars were once scoured by torrents of running water, producing branching networks of valleys and huge outflow channels like that onto which the Mars Pathfinder spacecraft landed. Today, however, liquid water is not stable anywhere on the Martian surface.

Models of the bulk composition of Mars based on the SNC meteorites curiously indicate a planet with a low water abundance but high concentrations of other volatile elements. This might be explained by reaction of water and metallic iron in accreted materials, stripping the oxygen from water to form iron oxide with the resultant loss of hydrogen from the planet. The interior of Mars would thus be dry and highly oxidized. Partial melting of the Martian mantle produced the magmas that crystallized to form SNC meteorites. These magmas were rich in oxidized iron but poor in water. Consequently, the amount of water outgassed from the Martian interior over time has probably been modest. Expressed as a global ocean of uniform depth, the outgassed water on Mars may amount to no more than a few hundred meters, compared to 2.7 km for the Earth.” (274)