Today's Reading
INTRODUCTION: A MESSAGE FROM OUR PALE BLUE DOT
Red puffy clouds fill an orange sky, high above the purple moss that dots the few exposed islands on the horizon. Waves break on the small stretches of shore, glittering in the red light from the sun overhead. You wait for the sunset and the darkness of night, but they never come. To experience nightfall, you have to travel for days to the far side of this distant planet, a place of eternal dusk. Even farther on, the dim light recedes, turning the landscape into a never-ending night.
The conditions greeting you on the night side of the planet are staggeringly different. The beam from your flashlight only penetrates the pitch-black of your immediate surroundings. It allows just a narrow glimpse into an unfamiliar world populated by life-forms you've never before encountered. In the gloom, you can just make out tiny bright specks of light, a biofluorescent glow that paints a slightly green sheen on the eerily alien landscape.
But the organisms here are perfectly adapted to the perpetual night. Having always lived in total darkness, they do not require the sun's light for energy or to assess their environment. By sensing heat and sound, they perceive the world as clearly as humans do with sight. Like creatures in the deepest, darkest parts of Earth's oceans, they are strangely familiar and yet not at all.
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Are we alone in the cosmos? The question should have an obvious answer: yes or no. But once you try to find life somewhere else, you realize it is not so straightforward. Welcome to the world of science, which always starts with a (deceptively simple) question.
We live in an incredible epoch of exploration. We are discovering not merely new continents, like the explorers of old, but whole new worlds circling other stars. Since the first extrasolar planet was discovered in 1995, astronomers have found more than five thousand others in our cosmic neighborhood. Astonishingly, that means about one new world discovered for every other day since we built the first instrument sensitive enough to detect them. And we have only spotted the ones that are easy to find—the tip of the iceberg.
Planets are so common that they circle most stars. And our galaxy, the Milky Way, hosts about two hundred billion stars. This staggering number indicates that there are billions and billions of new worlds to explore in our galaxy alone. The imaginary planet I described above could be one of them, half dipped in constant sunlight and half in never-ending darkness.
We are not discovering these new worlds in ships, not even ones designed to sail through space, because these exoplanets are trillions of miles away. Those vast distances make the search much harder. But light and matter interact, which gives us a way to explore these new worlds on our cosmic shore—even though we cannot reach them yet. Just as the stamps in a passport tell you what countries a traveler has visited, light contains information about where it has been on its journey. Signs of life are written in a planet's light—if you know how to read it.
Look up at the sky tonight and count the stars that you see. For thousands of years, humans have scanned the heavens and wondered if we are alone in the cosmos, but with limited means to explore an answer. What has changed is that now we know most of these stars have companions—they harbor planets too dim for you to spot. Could there be someone watching our Earth right now, also wondering if they are alone or not? For the very first time, we have the technology to investigate.
What should we be looking for in our search for extraterrestrial life? One astronomer half-joked that we might look for large groups of animals, like pink flamingos, on other planets, though they'd have to stand still long enough for us to spot them. Color is an important tool in our search for life, but luckily, searching for colorful flamingos on other planets is not our only option. Looking a little closer we find that our planet harbors an astonishing diversity of life that changes our air and the color of our world, from bone-dry deserts to the frozen ice fields of glaciers to the hot sulfur springs of Yellowstone National Park.
Although the forms of alien life will likely differ, these organisms provide clues for our search: a mixture of the familiar rules of physics and the laws of evolution should produce organisms that could be entirely unlike those we recognize but perfectly adapted to their worlds.
Today, solving the puzzle of these new worlds requires using a wide range of tools like cultivating colorful biota in our biology lab, melting and tracing the glow from tiny lava worlds in our geology lab, developing strings of code on my computer, and reaching back into the long history of Earth's evolution for clues on what to search for. With Earth as our laboratory, we can test new ideas and counter challenges with data, inspired curiosity, and vision. This interaction between radiant photons, swirling gas, clouds, and dynamic surfaces driven by the strings of code within my computer creates a symphony of possible worlds—some vibrant with a vast diversity of life, others desolate and barren.
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