Five Billion Years of Solitude by Lee Billings Read Free Book Online

be elusive as long as scientists only had one living world to study—our own. Drake didn’t believe they would remain intractable forever.
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    B ack in 1960, I thought that the possibility of detecting extrasolar planets in my lifetime was very, very low, though Otto Struve had already given us ideas about how it might someday be done,” Drake had told me back in his living room. “I thought our only hope of detecting evidence of other planets was to receive radio signals from any intelligent creatures on them. We’re seeing a similar pessimism play out now with characterization of planets around other stars. The techniques are there before us.”
    Already, planet hunters had found a handful of worlds that in theirmost basic details didn’t appear too dissimilar from Earth. Those planets, their numbers growing every year, could potentially be much like our own. But the methods used to find them relied on closely observing a planet’s bright, beacon-like star, not the dim planet itself; the gravitational pull of a planet on its star, or the shadow a planet cast toward Earth as it transited across its star’s face, generally only revealed such things as a world’s mass, size, and orbital properties. Without actually seeing these worlds—that is, collecting and analyzing photons reflected off their atmospheres and surfaces—scientists would be unable to determine whether any potentially habitable, potentially Earth-like planet was actually either of those things. They would be stuck where Drake had been fifty years before, hoping against all odds for a message from the stars to come streaming from the sky, filled with information on the flora, fauna, and environment of a place far, far away.
    During the nineteenth century, a series of incremental discoveries led to the breakthrough that enabled the bulk of modern astronomy: light emitted, absorbed, or reflected by matter changes its colors in a way that captures the matter’s chemical signature. Splitting up light into a spectrum to reveal those colors—a technique called spectroscopy—reveals those signatures, allowing astronomers to remotely measure the chemical composition of galaxies, stars, and planets. If they could somehow take a promising exoplanet’s picture by gathering enough of its reflected photons, researchers could use the resulting spectrum to investigate that world’s atmospheric chemistry. They could search for indicators of habitability, such as water vapor and carbon dioxide, as well as signs of life, like the free oxygen that filled and tinted our own planet’s skies. They could look for the glint of a parent star’s light shining off the smooth, flat surface of a planet’s oceans or seas, or even subtle changes in the color of land that would hint at photosynthetic plants. Astronomers using observations from satellites and interplanetary spacecraft had already performed all these measurements for the Earth, confirming that our living planet could, in theory, be studied from across the vast distances of interstellar space.Even if any extraterrestrials didn’t advertise their presence to the universe at large, techniques like spectroscopy offered hope that we could still find and study their home worlds.
    In the last decades of the twentieth century, as exoplanetology became a legitimate scientific field, planet hunters devised several ways to take planetary snapshots across the light-years. All involved one or more custom-built space telescopes designed to nullify a target star’s glare and reveal its retinue of planets. At a likely cost of several billion dollars, a single space telescope could be built capable of delivering images of worlds around nearby stars, each planet manifesting as a dot a few pixels wide—minuscule, but more than enough for atmospheric spectroscopy. If money were no object, a fleet of telescopes could be assembled in space or on the far side of the Moon to act as one giant instrument,