Field Guide to Meteors and Meteorites, O. Richard Norton and Lawrence A. Chitwood (2008)

If you want to touch something from outer space, simply form one of your hands into a fist. You will then be touching star-stuff, because every atom in every human was once heavenly. We eat star-cinders, breathe star-fumes and stand on the sky, because all terrestrial matter was once extra-terrestrial. This is because the fusional furnace of a star, unlike an ordinary furnace, creates complexity out of simplicity. Simple atoms like hydrogen and helium go in, complex atoms like oxygen and iron come out. I think that’s one of the important messages to take from this book: Up There is down here and always has been. O. Richard Norton is writing about stones that are special because they fall from the sky, but sometimes those stones are very hard to tell from ordinary stones, as the section called “Meteorwrongs” explains next to a photo of two very similar rocks:

One of these rocks is a meteorite. Note the rounded knobbly shapes in both that look like clusters of grapes. Mundrabilla (right) is an Australian iron meteorite. The knuckle-like knobs are large, randomly orientated iron-nickel crystals of taenite that stand out due to weathering. A pair of Moqui marbles (left) are concretions weathered out of Navajo Sandstone in the southwestern United States. The sand is glued together by the iron oxides, hematite and goethite. They are a terrestrial analogue to the hematite-cemented Martian blueberries seen from the Martian rover Opportunity in 2004. (“A Gallery of Meteorwrongs”, pg. 178)

Unless you’re an expert, distinguishing special sky-stones from ordinary earth-stones can be difficult. But are any stones really ordinary? I don’t think so. They all come ultimately from the belly of a star and they all raise this fascinating question: what is matter? The ultimate answer to that may be: Matter is mathematics. But maths is always present when you study matter and its behaviour, so there is a lot of maths in this book. In fact, the whole book is mathematical, because it’s all about chemistry, geology, petrography and various forms of physics: orbital mechanics, thermodynamics, optics and even acoustics:

The sound of a fireball is an altogether different experience. It is an eerie experience when a fireball begins its rapid journey across the sky. Trees and tall buildings cast long moving shadows… Seconds go by and not a sound is heard. Suddenly, without warning, the fireball explodes, scattering myriads of fragments that briefly maintain their courses among the stars. All of this happens in absolute silence. Seconds and minutes go by. The fireball vanishes. Still, silence. Then, when you least expect it, a tremendous series of explosions rock the silence. The fireball’s shock wave has finally arrived, announcing its presence by a series of ground-shaking sonic booms. These sounds are caused by pressure waves generated in the atmosphere by the hypersonic flight of the fireball. (chapter 3, “Meteoroids to Meteors: Lessons in Survival”, pg. 45)

Fireballs are rare, but meteors fall constantly and many people watch for them and photograph them, so this book is also about sky-stones you can see falling, not just about sky-stones you can pick up or stand on. After all, some never reach the ground. Huge numbers of meteors fall individually and unpredictably, but there are also periodic meteor-showers named after the constellations they seem to fall from, like the Aquarids, Leonids and Taurids, and associated with the debris-trail of comets. These can also be tracked using radar:

In the 1940s military radar operators noticed that meteors caused interruptions in high-frequency broadcasting reception, taking the form of whistles that rapidly dropped in pitch. Most individual meteoroids are too small to reflect radar waves back to the ground. Instead, radar waves sent from the ground were detected as they reflected off much larger targets, in this case, columns of ionized gas left in the wake of a meteor, formed when the particles evaporated passing through the Earth’s upper atmosphere. (ch. 1, “Interplanetary Dust and Meteors”, pg. 19)

In a way, radar was detecting the death-cries of the “Ancient Fragments of the Solar System” described in part one of this book: the asteroidal and cometary grit in the cosmic clockwork of the sun and planets. Bits of that grit have been falling to earth throughout man’s existence, but some sceptics, inspired by Newton’s apparent conquest of the heavens, decided it wasn’t there after all. When two scientists from Connecticut reported a meteorite fall in 1807, Thomas Jefferson famously said: “I would sooner believe that two Yankee professors would lie than that stones would fall from heaven.” He wasn’t just wrong, he was unimaginative too. Two hundred years later, we know better, but some knew better more than two millennia ago:

Diogenites are named for the fifth century B.C. Greek philosopher, Diogenes of Apollonia, considered to be the first person to suggest that meteorites actually came from beyond the Earth. They are called Plutonic since their origin appears to be plutonic rocks deep below the eucrite crust of the asteroid 4 Vesta. (ch. 5, “Primitive and Differentiated Meteorites: Asteroidal Achondrites”, pg. 122)

So fragments of asteroid existed on the earth before astronomers discovered the existence of asteroids. Fragments of Mars and the moon have been found on earth too, as Norton describes: big meteoric impacts there have blasted Mars- and moon-stuff free and some of it has fallen here. But Diogenes’ ancient insight about the origin of sky-stones didn’t influence their name: meteors are so-called because they were thought to be atmospheric phenomena. That is, a shooting star, or meteor, was seen as part of meteorology, not astronomy. When science learnt better, it created two more terms: meteoroid, meaning the physical object in space, and meteorite, meaning the physical object once it’s landed on the earth. You may have meteorites on your windowsills, because some of them are very small: IDPs, or Interplanetary/Interstellar Dust Particles, like the ones that stream from the tail of a comet as it approaches the sun. These drift to earth rather than drop, but they’re hard to tell from terrestrial dust. To study them more easily, scientists had to get away from the surface of the earth and Richard Norton describes how the “University of Washington’s Interplanetary Dust Laboratory” began to use “high flying aircraft” in the 1970s to collect this cometary dandruff (ch. 1, “Interplanetary Dust and Meteors”, pg. 9). Since then, the Stardust probe has actually collected samples from “the periodic Comet Wild 2 (pronounced ‘Vilt’)” and returned them to earth.

This is one part of astronomy that isn’t reliant on the ephemerality of photons, but photons can still tell us a lot about the chemistry of comets and asteroids, because light is influenced by the nature of the matter it bounces off or shines from:

In 1970, T.B. McCord and his coworkers at the Institute of Geophysics and Planetology, University of Hawaii, made astronomical history when they were the first to recognize similar characteristics between the spectra of 4 Vesta and a specific meteorite type. They compared the reflection spectra of the Nuevo Laredo achondrite with the reflection spectra of 4 Vesta. (ch. 2, “Meteorites: Fragments of Asteroids”, pg. 33)

Photons are important in other ways, as you’ll find in chapter 11, “From Hand Lens to Microscope”. Here astronomy meets petrography, or the study of patterns and colours in slices of rock under high magnification. The photographs in this chapter are some of the strangest and most beautiful in the book: “A calcium-rich clinopyroxene glows with bright second order interference colors” (pg. 218). But meteorites can be beautiful to the naked eye too, though sometimes they have to be cut open to become so. There’s gold and silver on page 171, for example, where you’ll see photographs of meteorites like:

Esquel, a main group pallasite. It was found in Argentina 1951 by a farmer while digging for a water tank. The meteorite shows beautiful yellowish green olivine (peridot) crystals… The Glorieta Mountain meteorite. When cut into a thin slab, polished and lighted from behind, this becomes one of the world’s most beautiful pallasites. (ch. 8, “Differentiated Meteorites: Stony-Irons”)

Pallasites aren’t named after the asteroid Pallas, but after the “German naturalist and explorer, Peter Simon Pallas”, who collected samples of a “1,600 lb meteorite found in 1749 near Krasnojarsk, Siberia” (pg. 168). Nearly two hundred years later, the Sikhote-Alin mountains in Siberia experienced a much bigger meteorite, seen as an “enormous fire-ball” on February 12, 1947, then collected as “thousands of beautifully sculpted iron meteorites… Today, Sikhote-Alin meteorites are highly prized in public and private collections throughout the world” (pg. 47). They’re black, not colourful, but the “flow-patterns” and regmaglypts – depressions like thumb-prints – caused by heat make them like attractive modernist sculpture. That Siberian fireball is described in in chapter 3, “Meteoroids to Meteors: Lessons in Survival”, which is about what happens to meteoroids as they plunge through the atmosphere. They heat up and sometimes break up, but they aren’t always sizzling when they hit the ground:

The temperature at 50,000-ft [15-km] altitude is about -50°F [-45°C]. This low temperature aids in rapidly chilling the falling rock. Long before hitting the ground the meteorite’s surface temperature has been reduced to between lukewarm and stone cold. The meteorite may even be coated with a thin layer of ice. In fact, some meteorites have been found minutes after landing, resting on top of a snow bank – without melting the snow. (pg. 45)

But sometimes meteorites are found millennia after landing, so the effects of water and weather are an important topic for meteorite-hunters. So are the effects of magnetism: you can use metal-detectors to hunt for meteorites, as Norton describes in chapter 10, “In the Field”. This is a field-guide, after all, but “field” can mean African desert, Swedish pine-forest and Arctic or Antarctic ice-sheet:

In the continental United States, the best hunting ground is in the southwestern part of the Mojave desert of southern California, where vegetation is relatively sparse and the climate is dry. Look for an old surface, one that has been exposed for a long time. Old dry lakes can be a good place to search. Many meteorites have been found in Rosamond, Muroc, and Lucerne dry lakes. (pg. 183)

The American meteorite-hunter Steve Arnold found his record-breaking “1,400 lb Brenham orientated pallasite” another way: “he dug it up from a depth of seven-and-a-half feet, locating it with the help of a high-tech metal detector” in 2005 (pg. 187). “Brenham orientated” is a reference to the way the meteorite was shaped by “ablation”, or the “removal and loss of… material by heating and vaporization” during its fall to earth (“Glossary”, pg. 267). But meteoroids aren’t just shaped by their encounter with the earth: they can also shape the earth, both geologically and biologically. The earth bears the scars of many past impacts, some of them cataclysmic in scale and epoch-making in their effects. Would man the mammal now rule the earth and watch the sky if it hadn’t been for the asteroid that wiped out the dinosaurs 65 million years ago? Or would an advanced, intelligent species of reptile be collecting and analysing meteorites now?

Questions like that aren’t just of historic interest: stones that fall from the sky are of huge practical importance, because big ones can wipe out not just cities and civilizations, but entire species, including Homo sapiens. The sky gave birth to all life on earth, because without the chemicals created there, life wouldn’t exist here. Life may even have begun there, but the sky has regularly committed infanticide too and man’s name is definitely on the hit-list. Sooner or later another giant sky-stone will hit the earth and cause megadeaths or worse, unless we spot it en route and stop it. That’s another message to take from this book: some meteoroids are beauties and some are beasts. All of them are interesting. This book explains how, what, where, and why, all the way from aphelia and bolides to xenoliths and the Zodiacal light.