One night in April, 2019, the skies above La Palmera, a village in northern Costa Rica, started to glow as a motorcycle-sized meteorite broke apart and scattered chunks of hot space rock over the rain forest below. It was just one of thousands of meteorites that hit the Earth every year, but this particular one, later dubbed Aguas Zarcas, caused a frenzy among experts. To the untrained eye, its fragments look like unassuming gray rock. But packed inside are a menagerie of organic molecules and space dust that predate the birth of our solar system.
Aguas Zarcas is among the most pristine examples ever discovered of a class of meteorites known as carbonaceous chondrites. It’s a deeply unsexy name, but these ancient space rocks are like time machines that provide windows into the universe as it existed billions of years ago. They’re unique geological records that detail the formation of amino acids in space, which some scientists believe may have been the abiotic grist that kick-started the evolution of life on Earth. They’re a rarity among rarities, prized by collectors and scientists, and are often worth more than their equivalent weight in gold.
Carbonaceous chondrites play a starring role in Meteorite, a new book by the University of Bristol cosmochemist Tim Gregory. But these bizarre extraterrestrial visitors are just one of a seemingly endless variety of weird and wonderful space rocks, and Gregory’s passion for his subject drips from every page. Meteorite is a mix of science and history that’s filled with anecdotes of close calls and happy accidents. Gregory strikes a good balance between hard science and the hard-to-believe, but he promises everything between the covers is true.
WIRED caught up with Gregory at home in Nottingham, England, to learn more about the book and why the best place to find a meteorite is at the end of the Earth. The following interview has been lightly edited for clarity and length.
WIRED: You work as a ‘cosmochemist.’ What is cosmochemistry, and how did you get into it?
Gregory: I’ve always loved rocks, and I’ve always loved space, as well. I discovered a couple of years into my undergraduate degree that there’s a discipline that combines both of them—rocks and space—and that’s cosmochemistry. It uses the same tools as geochemistry, but it just happens to be on rocks from outer space instead of the Earth.
What makes space rocks different from Earth rocks?
There are a few things that distinguish meteorites from Earth rocks. The most obvious one is their age. Almost all meteorites we’ve discovered come from asteroids, and they cooled down very quickly after they formed. The Earth has an internal heat engine through the decay of radioactive isotopes that is still powering volcanic and tectonic processes. So the Earth is still geologically active, whereas the geological processes on these asteroids was very short-lived. So the rocks that come from these places, the meteorites, haven’t changed much at all in the last four and a half billion years. They’re far older than the oldest Earth rocks.
How can you tell a meteorite from any other rock on Earth unless you see it fall to the ground?
Meteorites look exactly like Earth rocks, so we have to go into the chemistry and look at their isotope composition. There are very subtle chemical differences that sort of prove their extraterrestrial origin. They come from fundamentally different worlds, which inherited a slightly different blend of chemicals when they formed. With the meteorites, there’s no way that you can find that sort of chemical fingerprint on Earth unless it came from another world.
Where do scientists find their meteorites?
We’ve got about 60,000 meteorites in the worldwide collection, and most of them came from Antarctica. There are a few reasons for that. The first one is really obvious: Generally, meteorites are really dark when they land on the surface, and ice is white. So they stand out like a sore thumb on the ice sheet.