Sarah Stewart Johnson

The precision of the map allowed Maria to read the planet’s history like a type of braille. As hinted by the initial data, the northern hemisphere proved to be the smoothest surface that had ever been observed in the solar system. Most of the terrain seemed to tilt slightly to the north, suggesting that a planetwide drainage system may have once emptied there, into a great northern ocean. Inscribed onto the surface was even a possible shoreline, Deuteronilus, which could be traced for thousands of kilometers. The coast ran along nearly the same elevation, with variations that could be explained by the ground rebounding, exhaling as the weight of a sea of long-gone water evaporated. With each new detail Maria plotted, another aspect of Mars’s history came to life. 
     Mars Global Surveyor changed what it meant to see a planet. If the old map of Mars was a simple picture, the new map was a portrait. It went beyond what our eyes could take in, capturing data on contours, on composition, on forces we could not see—not just topography but things like magnetic signals and mineral compositions measured out beyond the visible wavelengths. There were subtleties to be seen—we just had to get there, and when we got there, we had to know how to look.

Excerpt(s) from The Sirens of Mars: Searching for Life on Another World by Sarah Stewart Johnson, copyright © 2020 by Sarah Stewart Johnson. Used by permission of Crown Books, an imprint of Random House, a division of Penguin Random House LLC. All rights reserved.

ALH84001 was a glimpse into a future brimming with possibility. What if life on Mars was completely different from life on Earth? Every organism we knew, down at the molecular level, was just the same: DNA-based, with DNA coding for RNA, RNA coding for amino acids, amino acids coming together in proteins, and proteins building cells. What if those tiny Martian cells were built on an entirely different biochemistry? Perhaps the answers were inside a meteorite. Perhaps the rock would reveal the underlying constitutional nature of life—perhaps even evidence of a separate genesis. Or, if those cells bore fundamental similarities to life on Earth, it might suggest universal laws of biology, just as there were universal laws of physics and chemistry. In these ways, when ALH84001 fell to Earth, it had landed us on the brink of discoveries so profound that they promised to transform the very nature of science.

Excerpt(s) from The Sirens of Mars: Searching for Life on Another World by Sarah Stewart Johnson, copyright © 2020 by Sarah Stewart Johnson. Used by permission of Crown Books, an imprint of Random House, a division of Penguin Random House LLC. All rights reserved.

Before the end of the mission, Mars Global Surveyor also took the first photograph of Earth from another planet. [...] I remember staring at that picture on my computer. I had searched for it, dragging the image to cover the screen, making it as large as I could. Earth seemed impossibly distant, but it was still recognizable. It was a crescent, more than half dark. The moon was next to us, with the same shadow. 
     As I peered at the pixels, trying to resolve the tiny squares of blue and green and white, I thought about where I was in the picture. In the frame, so much had been captured, and obscured. I was there somewhere, going about my life the day it was taken. I wondered if I’d been cooking a white-bean soup or sleeping in a rumpled bed when the shutter clicked, or gazing through the heavy glass window of the library at the rain outside. Perhaps I was sitting under a magnolia tree, or rushing across a crowded city street, midway through an infinitesimal step. Perhaps I was lost in thought somewhere, wondering if I had what it took to be a scientist, wondering who would show me the way. 

Excerpt(s) from The Sirens of Mars: Searching for Life on Another World by Sarah Stewart Johnson, copyright © 2020 by Sarah Stewart Johnson. Used by permission of Crown Books, an imprint of Random House, a division of Penguin Random House LLC. All rights reserved.