This is a piece of Mars, the planet. It came to me via a meteorite, Dar Al Gani 476, some 60,000 years after it plopped itself down in the Libyan Sahara, to later be discovered on May 1, 1998. This particular piece is about the size of your thumbnail, assuming you’re not some kinda freak with abnormally sized thumbnails. It weighs in at a hefty .240 grams.
It was evicted from Mars with significant force some 1.1 million years ago, as a completely different, and much larger meteorite slammed into Mars with enough force to blast chunks of the planet clear into space, out of Mars’ orbit, and into orbit around the Sun, where they chilled out for a while, until a few of them eventually ran smack into Earth. DAG 476 was the 13th meteorite from Mars to be found, giving it the nickname “Lucky 13”. It was the first to be found after ALH84001 was made famous in all that brouhaha about whether or not it contained traces of life, which unfortunately, it probably doesn’t.
DAG 476 is an achondrite, belonging to a class of meteorites known as the SNC group, which stands for Shergottites, Nakhlites, Chassignites, of which all members originate from Mars. DAG 476 is of the Shergottite variety, which got its name from the Shergotty fall in 1865 in India. It’s the most common sub-group of martian meteorites, having characteristics which suggest they solidified at, or near the surface of Mars out of magma from deep beneath the surface. They don’t all come from the same place on Mars though, which means this has happened many times. The composition of DAG 476 matches up perfectly with 4 other martian meteorites, DAG 489, DAG 670, DAG 735 and DAG 836, suggesting that all five were probably from the same body that broke up upon entry into our atmosphere. There are about 30 different distinct meteorites known to be from Mars in total, if you count the multiples as one. As a consequence of lying there on Earth for 60,000 years, the original fusion crust generated on entry into the atmosphere has long since eroded away, with veins of carbonate running through the occasional crack due to weathering. I think those are the light greyish parts at the top, running down the left side, but I’m pulling that straight out of my ass, without any confidence whatsoever.
It’s kind of astonishing how much Science can tell us about this rock. It crystallized originally to form a rock about 474 million years ago, which is actually quite young, by meteoritic standards, just a meter or two below the surface of Mars. They can tell how deep it was buried by the rate at which it cooled, which affects the crystallization process. There are shock features within, that point to it experiencing enormous shock, as it was blasted free of its homeworld, into space. Incidentally, the age of 474 million years would also imply that there was volcanic activity on Mars less than half a billion years ago. Geologically speaking, that’s pretty recent. The alignment of the olivine, and pyroxene crystals within it indicate that it formed in an extruded lava flow. I guess that means they’re stretched in one direction. If Mars was geologically active 474 million years ago, there’s probably at least *some* activity today. Perhaps not full fledged eruptions with lava flows, but it’s fairly likely that there is something. When it was floating around in space, it was being bombarded by high energy cosmic rays, which are capable of smashing the atoms they collide with into smithereens, or being absorbed by them, turning into new, radioactive elements, like Helium-3, and Argon-38. By measuring the relative quantities of these gasses, it can be determined how long it was in space. When this rock landed on Earth, Man was just getting the knack of making stone tools.
How do we know it’s from Mars? Well, back in the 1970s, one of the things the Viking landers did was sample the atmosphere on Mars, characterizing the relative abundances of gasses in the air. It also sampled the soil, to determine the chemistry. Inside this meteorite are wee little microscopic bubbles of trapped gasses that have been locked up in there ever since this rock formed, trapped inside of crystal cages. Wouldn’t you know it, when sampled, those bubbles turn out to have the exact same proportion of gasses as the Martian atmosphere did, when measured by the Viking landers. The composition of the rock itself is very similar to the composition of rocks on Mars. In a neat scientific coincidence, one of the Mars meteorites, known as EETA79001, discovered in Antarctica in 1979, was found to be highly similar in composition to a rock nicknamed “Bounce” that was studied on Mars, by the Opportunity Rover. The data seems to indicate that Bounce itself is from elsewhere on Mars. It was also ejected in an impact, but not with enough energy to get launched into orbit around the Sun. It’s conceivable that Bounce is even from the same event as EETA79001, it’s at least likely to be from the same place on Mars. What are the odds of finding pieces ejected from the *same* meteorite impact on two different planets? It boggles the mind.
This is my single most treasured possession. What could possibly beat a piece of another planet? I can point to it in the sky, and say “Yup, I’ve got a piece of that.” It’s tens of millions of miles away, and it’s on my bookshelf. It’s the only place in this solar system where we can seriously see ourselves living one day, in our craziest dreams and hilariously bad movies, perhaps not even in bubbles, or space suits. It’s the only place remotely similar to Earth. And it was generous enough to send a souvenier all the way here, to inspire us to dream big, so that one day, if we’re good little human beings, and we don’t kill ourselves first, we can go to Mars, and steal all that precious, precious land. The best part? There aren’t even any natives to oppress/subjugate/relocate/eliminate! No guilt, and we get all the casinos to ourselves!