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.
