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The following is an excerpt from The Sirens of Mars: Searching for Life on Another World by Sarah Stewart Johnson.

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The Sirens of Mars: Searching for Life on Another World

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Chapter 11: Form From a Formless Thing

Deep in the forests of western Bosnia is a village named Jezero. In many Slavic languages, “jezero” is the word for lake, and jezeros stretch all along the Adriatic. They fill the Julian Alps, dotting the spaces between low-lying meadows and frog-filled caves. There are sinkhole jezeros and karst jezeros, glacial jezeros and jezeros linked by a hundred waterfalls. But the jezero in the village of Jezero is green and quiet, almost mythic. It’s preternaturally still, rumored to be heavy with deuterium. The surface reflects the clouds like a piece of polished glass.

Small craters on Mars are named after small towns, and on the western edge of Isidis Planitia is a small crater named for this small Bosnian town. Early in Mars’s history, Jezero Crater also held a lake with water that reflected the sky. Two rushing rivers emptied into the cavity—one from the west and one from the north. The lake was deep, its crater floor plunging hundreds of meters down from the rim, which on one unexpected day billions of years ago suddenly fissured, unleashing a catastrophic torrent of water over the side.

Among the bevy of spacecraft that will soon launch toward Mars is a NASA rover that will land on the spill of lava that covers the floor of Jezero Crater. The mission’s breathtaking goal is to collect samples from Mars to be brought back to Earth at some later date, samples that not only may harbor signs of ancient life but also could give us an unprecedented look into the history of our solar system.

Here on Earth, our record of deep time has been forever lost. The seas have lifted into rain, and the rain has beaten the surface bare. Our planet has swallowed itself, plate by plate. Our original crust has almost completely disappeared; all but a few patches have been dragged back into the interior. The small blocks of rock that remain—in the cherts of Australia and the greenstone belts of Greenland—have been cooked, mostly beyond recognition. Our early days are irrecoverable.

If we are going to archive samples of Mars, now is the time. One day, potentially one day soon, there will not only be rovers and robots, there will be people exploring the planet.

Mars, however, is all past. It is as if time stands still. There are no plate tectonics, no large-scale recycling of rocks. The rivers have stopped; the temperatures have plummeted. On the scale of humanity, Mars has been constant. To be sure, there is weather, like the spectacular dust storms that come and go. Barchans of sand shift across the surface. The polar caps wax and wane. The planet’s spin axis arcs into a deep bow every hundred thousand years or so. Yet the land beneath remains.

The place we’re now visiting with spacecraft is almost the same world that it was three billion years ago. As a result, the right samples may even help us fill in the gaps in our own planet’s history. Right now it’s unclear what prebiotic chemistry dominated the early days of the rocky planets, or what dance of reactions made the first protocells. Perhaps life sprang from geothermal fields, with repeated cycles of wetting and drying helping to form complex mixtures of important molecules. Or perhaps not. The samples the rover collects might hold within them the echoes of the beginning of life, entombed deep in the planet’s ancient rocks.

The rover’s chassis is the same as Curiosity’s, but it will carry a different scientific suite, even a small helicopter to test the viability of airborne craft. The rover’s two-meter-long arm, laden with new coring tools and instruments, looks like an outstretched lawnmower, and is just as heavy. Over at least two years of operations, the turret will drill several samples of rock and place them carefully in sample tubes, each about the size of a penlight. The rover will then deposit the tubes in a little pile on the surface. The cache will remain there for many years, glinting in the sun, until a fetch rover comes and launches them into orbit—to be caught by a passing spacecraft and brought home.

Like the rocks we carried back from the moon, Mars rocks will be analyzed for decades to come. Once we have them in hand, we’ll have them forever. It’s been nearly fifty years since the last humans walked on the moon, yet the Apollo samples have been examined again and again, particularly as new tools and technologies have been developed. In that time, we’ve discovered astonishing, unexpected things, like the precise age of the moon and the fact that the rocks carry an indelible record of the history of solar activity.

If we are going to archive samples of Mars, now is the time. One day, potentially one day soon, there will not only be rovers and robots, there will be people exploring the planet. SpaceX is already calling for a million passengers, sent on a thousand spaceships. But unlike rovers, which we can bake and clean, humans will shed life left and right, sloughing off cells, littering the planet with biological material. The next decades are thus critically important for the search for life because the window to explore an untrammeled planet—a pristine record of the past—is closing.

Click here to download an additional chapter, Chapter 1: Into the Silent Sea, from Sarah Stewart Johnson’s The Sirens of Mars.

Excerpted from The Sirens of Mars by Sarah Stewart Johnson. Copyright © 2020 by Sarah Stewart Johnson. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.