The tally grows like digits ticking up on the take-a-number display in a New York deli. 1,876 extrasolar planets as of Jan. 9th this year. 475 of them are multiple planetary systems or true solar systems around other stars. Most are huge, gaseous, beefier than Jupiter and searingly close to their host stars to be happy places for life.
Of the 1,876, just 28 lie within their stars' habitable zones where liquid water can pool and remain on the surface long enough to offer the potential habitat for life as we know it. Drilling down further, only 10 of the 28 are similar in size to Earth. Yet based on data returned by NASA's Kepler exoplanet mission, scientists estimate there could be more than 40 billion Earth-sized planets in the Milky Way alone.
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Astronomers constantly refine and build new equipment to track down ever-smaller planets with the hopes of finding more clement Earth-like worlds. Enter the Next-Generation Transit Survey (NGTS), a system of dozen wide-field 8-inch (20 cm) telescopes, designed to discover transiting exoplanets of Neptune-size and smaller around stars as faint as magnitude 13. Hosted by the European Southern Observatory (ESO), the project is based at Paranal Observatory in southern Chile, where the skies are exceptionally dry and clear.
NGTS is fully robotic and optimized to detect bright but relatively small and cool orange and red host stars. These stellar dwarfs are not only the most numerous stars in the universe, but they burn their nuclear fuel frugally, giving them very long lives. Those factors in turn increase the potential for habitability.
As a planet passes in front of its parent star it produces a slight dimming of its light that sensitive equipment attached to the telescopes will record. By studying the periodic brightening and fading of a star's light, astronomers can determine the size, mass and other characteristics of an orbiting alien planet.
NGTS will continuously monitor the brightness of hundreds of thousands of comparatively bright stars in the southern skies with an accuracy of one part in a thousand, a level never attained before with a ground-based survey.
It may also be possible to probe the atmospheres of the exoplanets. During the transit some of the star's light passes through the planet's atmosphere, if it has one, and leaves a tiny but detectable signature. To date we've uncovered basic atmosphere compositions of a few planets, but NGTS should provide many more potential targets.
