Contemplated but impossible to observe for centuries, the first planet beyond our solar system was discovered just over two decades ago. Using complementary space missions and ground-based observatories, scientists have ushered in a golden age of discovery of worlds in planetary systems far beyond our own.
As of July 2014, nearly 1,740 of these exoplanets – planets beyond our solar system – have been confirmed, with at least 450 of these in systems with more than one planet. Using these detections along with clever mathematical methods to estimate planets they cannot observe, scientists conclude that there could be as many as two planets for each of the roughly 200 billion stars in our galaxy alone. Of these, estimates range from about 10 billion to 40 billion that would be Earthlike and in the so-called habitable zone: the distance from a host star where water, and therefore life, could exist on the planet’s surface.
While not evidence of extraterrestrial life or intelligence, the current optimistic estimate of billions of habitable worlds in our galactic neighborhood has certainly enhanced scientific interest in the search for life beyond not only Earth, but the solar system.
Leading the search for new “Earths” is the Kepler space observatory. Launched in 2009, Kepler’s primary directive is to search for exoplanets that are Earth-size or smaller by observing the dimming of light caused by the planet orbiting in front of its host star. This method has unveiled a parade of the fabulous and strange. Sizes range from rocky bodies even smaller than Earth to supersized leviathans of gas or ice, many times the size of our largest planet, Jupiter. There is also an array of other alien bodies, including exotic “hot super Earths,” “mini-Neptunes” and free-floating orphan worlds, devoid of host-star or planetary neighbors. Further, we now know that stable exoplanetary systems can orbit two, three, four and even more host stars. Imagine waking up to a sunrise on one of these worlds!
Sometimes I wonder why, with all these potentially habitable worlds, our galaxy is not an obviously teeming metropolis of life and interstellar travel. In spite of this, we can still say with confidence that at least as far as planets go, we are certainly far from alone.
You can learn more about planets and the evolution of solar systems by visiting the astronomy, astrophysics and meteorite exhibits adjacent to the Astronomy & Astrophysics Research Lab at the N.C. Museum of Natural Sciences.
Rachel L. Smith is director of the Astronomy & Astrophysics Research Lab at the N.C. Museum of Natural Sciences and assistant professor in the Department of Physics & Astronomy at Appalachian State University.