Antarctica (17 page)

The biggest clue to a meteorite, though, would be its fusion crust, the molten outside layer formed as it tore through the atmosphere in a blaze of heat and light. Fusion crusts are usually very dark brown and uniform, somewhere between glossy and matt, as though someone had painted a layer of dark chocolate on the outside. At its simplest, the rocks around us were mainly pale, and we were looking for something dark.

But time was running out. We only had sixty minutes assigned ground time and if we didn't radio in to Mactown soon to confirm that we were lifting off, we would trigger an automatic Search and Rescue Mission. And then, when it was almost too late, when Barry and I were still peering rather hopelessly at rocks with John a tiny multi-coloured figure in the distance, we suddenly saw him beckoning. ‘Come here,' his voice floated over the ice. ‘I've found one!' We ran to meet him, skidding and sliding on the glassy blue surface. ‘There it is,' he beamed, gesturing at a small brown stone, ‘the oldest rock you'll ever see.'

About an inch or so in diameter, John's find was an ordinary chondrite, typical in every way. One end had been sheared off, revealing medium-sized crystals and a few small chondrules. The unbroken side was smooth and rounded, like a pebble in a stream. And, yes, there was the dark chocolate coating, too. It was textbook. We took turns lying flat on the ice, having our picture taken beside a genuine rock from space.

Being there at the find really is a thrill. But in meteorite terms ours was still ‘ordinary'. Researchers now have thousands of these chondrites to prod and grind and test. They make up the vast body of meteorite finds the world over.

Rarer are the achondrites, the ones without little solidified blobs of pre-planetary putty. These must have come from bigger bodies, asteroids large enough to get some internal heat going. Some asteroids are large enough to begin to separate out into an internal iron core and lighter crust, which is why we can find meteorites on Earth made entirely of iron, or with other strange compositions. The truth is, everyone secretly wants to find the special ones, the achondrites. Because although most of these come, like the ordinary chondrites, from the asteroid belt, a handful come from somewhere else entirely.

 

18 January 1982, Allan Hills Main Icefield

If it weren't so close to the end of the season, John Schutt might have delayed the trip. The sky was already grey by breakfast time and it was getting greyer. John wasn't worried about a snowstorm. This was the high desert where snow almost never fell. But if the clouds descended low enough, they could lose all the shadows. That's OK on the blue ice patches, but in between, where everything was white, no shadows meant no surface definition. And that meant the wind-sculpted sastrugi became all but invisible, making it perilously easy to overturn a skidoo. Worse, in these days before satellites could pinpoint you wherever you went, if you couldn't pick out your own tracks in the snow you might never get home.

But there was a new arrival in camp, Ian Whillans, who had come in from Mactown just two days before. Ian wasn't an expert on meteorites, but he knew a lot about ice and he wanted to check out the meteorite sites for himself. While the rest of the team stuck around camp, John had offered to take Ian out to the Middle Western Icefield a few kilometres away.

Anyway, John knew the terrain better than most. As the two of them fired up their skidoos and roared out of camp, he kept a watchful eye on the descending clouds as well as on the ice around him. Nobody knew if there were meteorites to find but up here where there were no earthly outcrops to distract you, anything dark had to have come from space. So they'd look around, take a few pictures, and maybe—if they were lucky—find a few rocks.

When they reached the ice field, the two companions spread out. Almost immediately, off in the distance, John saw Ian stop and wave his arms. Beginner's luck. Ian had clearly found his first ever meteorite. But when John went over to check it out he was baffled by what he saw. Though he'd seen a few hundred meteorites by then, he'd never seen anything like this. The rock, which was about the size of a golf ball, had a weird fusion crust that seemed to be some kind of frothy green glass. Part of it had sheared off and inside were chunky angular fragments of a white mineral called feldspar, making a sharp contrast with the dull grey background.

John opened his collection kit and pulled out an aluminium strip. He punched the number—1422—into the counter and held it over the meteorite while Ian took what is now one of the programme's most famous pictures. Then he carefully bagged it and wrote this in his notebook:

 

#1422—Strange meteorite. Thin, tan-green fusion crust, ∼50%, with possible ablation features. Interior is dark grey with numerous white to grey brecchia (?) fragments. Somewhat equi-dimensional at ∼3 cm.
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In retrospect, everyone involved said they should have known immediately where this new meteorite had come from. To a trained eye, John's description had all the right clues. But though there was mild interest back in camp at this strange specimen, it went into the pot with all the rest and was promptly forgotten.

Even when the meteorite finally reached Houston several months later, it wasn't the first one to be processed. Perhaps John should have put a few more exclamation marks in his description. Knowing what he knows now, he would also probably not have stinted on the capital letters. But back then, the curators didn't turn to meteorite #1422 until they had already processed four others. So it became ALH81005, the fifth to be processed from the Allan Hills region, from finds made in the season beginning in 1981.

But when the researchers at NASA's Johnson Space Center (JSC) took a closer look at the meteorite, they began to understand the significance of this physically small but scientifically giant find. And the bevy of researchers who clamoured for tiny fragments to test confirmed these suspicions. Those white chunks that John had so faithfully recorded turned out to be anorthite, the chalky mineral that makes up most of the lunar highlands. ALH81005 hadn't come from the asteroid belt or anywhere near. It had come from our very own Moon.
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This was nearly fifteen years after the Apollo programme had brought back abundant quantities of Moon rocks. Any geologists worth their salt knew that large parts of the lunar surface were made up of fragmented white anorthite in a pale grey background. Why did none of the experts who had already seen the sample manage to identify it?

The main reason for this collective snow blindness is that it simply shouldn't have been possible. According to the wisdom of the day, meteorites could only come from asteroids. The energy needed to break off a piece of another planet and blast it into the sky should have pulverised the rock. And even if a fragment did survive long enough to escape its home planet's gravity, it would be just one small speck in the infinite blackness of space. Small chance that it should fall on to the Earth, and infinitesimal chance that anyone should find it. But that reckoned without the concentrating power of the Antarctic ice. Just as we had gone to the Moon, so the Moon had now come to us. And if chunks of the Moon could be chipped off and survive long enough to arrive on the surface of the Earth, perhaps pieces of other planets could come to us, too.

 

The first to appear was the Chassignite, a four-pound lump of extra-terrestrial rock that landed in Chassigny, France, at 8 a.m. on 3 October 1815, just months after the Battle of Waterloo. It was followed on 25 August 1865, at 9 a.m., by another peculiar meteorite that fell near Shergotty in India. Like the Chassignite, this one was hefty, weighing in at ten pounds. Also, like the Chassignite it looked different from the normal run of meteorites. It had no chondrules. Its crystals were more like those from earthly rocks that had melted in the heart of volcanoes. It also turned out to be disturbingly young. Meteorites from the asteroid belt all date back to the first days of the Solar System, and they are uniformly 4.5 billion years old. This new meteorite, dubbed a Shergottite, measured its age in the mere hundreds of millions of years.

And at 9 a.m. on 28 June 1911, a shower of at least forty stones fell near the village of El Nakhla El Baharia, twenty-five miles east of Alexandria in Egypt. One of the stones reportedly killed an unlucky dog. By the late twentieth century, it was clear that this ‘Nakhlite' bore striking similarities to the Shergottite. It was born in lava, and, though older than the Shergottites, by meteorite standards it was still extremely young.

These three meteorites collectively gave birth to a new category of alien stones, affectionately known as SNCs (pronounced ‘snicks') for Shergottite, Nakhlite and Chassignite. Over the years, more SNCs showed up and by 1980 nine had been found, including three in Antarctica, but nobody knew what they were. They existed on the fringe of meteorite research, in an undefined category of their own. And yet, certain researchers had begun to murmur about the SNCs. If they were volcanic, and they were young, they had to have come from a body big enough to have internal heat and violent eruptions. And that meant a planet. An alien planet.

But nobody spoke too loudly because this, of course, was impossible. Or so it seemed until sample ALH81005 hit the big time. If a meteorite could come to us from the Moon, what were the chances—whisper it—of rocks also coming to us from Mars? In 1983 something happened to turn the whispers into a roar.

EET79001 was clearly a SNC. The ANSMET posse had found it near a scattering of Earth rocks called Elephant Moraine in 1979, and the rock was peculiar enough that the curators at Johnson Space Center had unwrapped it first. It weighed a hefty eighteen pounds and, like the other SNCs, was made from cooled solidified lava. But when researchers sawed through, they found some odd dark blobs that stood out starkly against the pale grey background. Whatever had smashed this rock off its first home had also compressed it with a shock wave of energy. As the rock relaxed, parts of it had melted, creating these glassy blobs along tiny fracture lines. And while they were still liquid, the blobs had dissolved a little of the atmosphere around them. Tiny bubbles, trapped inside these dark receptacles, might yield a vital clue about where the rock had been born.

Encouraged by the new lunar finding, in 1983 researchers re-melted, collected, measured, and held their collective breath. And the results as these minuscule whiffs of gas were released from their glassy prison were unequivocal. They looked nothing like the composition of our own earthly atmosphere, but exactly like the elements that remote satellites and robot space missions had already measured on Mars.
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The SNCs were definitely Martian.
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Though the world had, by this time, sent several space missions to our nearest planetary neighbour, and there were many more to come, a sample return was (and still is) a very distant prospect. We can measure the planet remotely, but it will be a long time before we can bring a piece of it back. But the Antarctic ice had shown us something that we would otherwise scarcely have believed. Earthbound people, many of them, had already held a piece of the Red Planet in their hands.

This was exciting news indeed, and yet all the SNCs hailed from relatively recently in Mars' history, from the days when the planet itself was in late middle age, cold and drear and almost certainly lifeless. That's not particularly surprising. Mars bears an impressive belt of volcanoes including Olympus Mons, the largest in the Solar System, which is three times the height of Mount Everest and stretches for more than 600 km. Much of the Martian surface has been repeatedly swamped with outpourings from these melting mountains, leaving older surfaces deeply buried. Small wonder, then, that the SNCs were all so young, and that none of them reached back to the wet Noachian Epoch, when water was apparently abundant on the Martian surface, and the planet might even have supported life.
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But imagine this, for a moment. If an asteroid happened to hit one of the rare remaining older surfaces; if its strike were glancing enough that it didn't pulverise the surface, but forceful enough that it ejected a chunk of rock with an escape velocity of 12,000 mph; if that chunk, flung out into space, wandered aimlessly for a million years or two before feeling the gravitational tug of a nearby planet; if it tore through the atmosphere of that planet in a blaze of glory and landed on one of the planet's frozen ice caps; if the chunk was buried in snow, squeezed, shoved and harried until it re-emerged, blinking, into the strangely blue daylight; and if, tens of thousands of years later a few local bipeds happened upon it, might it contain signs of alien life? If so, it would surely become one of the most exciting pieces of real estate in the entire Solar System.

 

27 December 1984, Allan Hills

It had already been a great day. The ANSMET team had been searching the far western ice field, back and forth, in the bright sunshine. After lunch, with a good haul already in the bag, they rewarded themselves with a jaunt. Along the top of the nearby escarpment was a fairyland of ice towers and wind scoops and giant sastrugi. There were huge wind-sculpted pinnacles up to 10 m high and crevasses filled with hard snow, pounded and packed in by the winds. When the light was just right, the pinnacles could shine as if they were on fire. It was a magical place for a little rest and relaxation.

The team swooped along the crest of the escarpment for a while, catching the glimmer and mood, before it was time to head back down, get back to work, do a few more passes before the end of the day. On the way down they hit patches of bare ice among the pinnacles. Instinctively the six of them spread out on their skidoos, eyes suddenly peeled. And there, on a gentle slope, lying on a small patch of ice, was a chocolate-brown squarish chunk of rock, about the size of a grapefruit. It was an achondrite, with no little round chondrules to mark it out as part of the Solar System's early builder's rubble. It had been born from melted rock, in a volcano. Maybe it was just a trick of the light, but it had a greenish tinge. The team photographed it, bagged it and threw it in the backpack.