NASA has three new top candidates for planets that might be habitable. According to the space agency,the Kepler telescope has discovered three new planets that are just the right distance from their parent stars to be temperate enough to sustain life.
The scientists have not yet determined the masses of the planets, but they all appear to be just slightly larger than Earth. Their moderate size, combined with their optimal distances from the sun, open up the possibility that they just might hold two rocky surfaces and liquid water — two key prerequisites for life as we know it. The three planets are as follows:
Kepler-69c: About 2,000 light years away, it is 70% larger than Earth and orbits a star that closely resembles the Sun. The researchers estimate that this planet completes one orbit around its sun every 242 days, somewhat more like Venus than Earth. Its orbit places it on the inner edge of the habitable zone, meaning that it is probably a bit too warm for our comfort, albeit not too warm to sustain some kind of life.
Kepler-62e: Orbiting the star Kepler-62, this planet is a relatively closer 1,200 light-years from Earth. It is also closer in size, dwarfing Earth by only 60%. A Kepler-62e year is 122 days. According to William Borucki, Kepler science principal investigator, this planet might be a rocky world like Earth or, alternately, a “water world” whose surface is one vast ocean. Either way, it would be quite habitable.
Kepler-62f: This planet also orbits Kepler-62. It is the smallest of the three, being only 40% larger than Earth. And its orbit is perhaps the most comparable to Earth: Projections are that it completes one rotation around its sun every 267 days.
Kepler, a space-based telescope that simultaneously observes more than 150,000 stars in the Milky Way, is the first NASA mission whose instruments are refined enough to catch views of Earth-sized exoplanets—e.g., planets located in other star systems. Since its deployment into orbit around Earth in 2009, it has enabled scientists to find more than 2,740 exoplanets. Of those 2,740 candidates, NASA astronomers have verified 122 as bona fide exoplanets.
A number of those confirmed planets are gas giants, similar to our solar system’s Jupiter, ruling them out for habitability. To meet the criteria, a planet must be terrestrial and must resemble Earth in size, generally lying within one-half to twice Earth’s mass. This comparably smaller size makes them much harder to spot.
Whatever the planets’ size, gas giant or small terrestrial planet, Kepler cannot provide actual views of the planets themselves. The glare of their stars drowns most of them out, and the telescope instead registers the tiny dips in a star’s light that a planet causes when it passes in front of it. Scientists analyze the data on the light curves to figure out if it really is the result of a planet.
More direct views of these other worlds might not be too far away, though. Researchers at NASA’s Palomar Observatory, near San Diego, California, are experimenting with new “adaptive optics” telescopic systems that would theoretically filter out the light radiating from a star so that the researchers can see any planets that orbit it.
The new system went online in June 2012, and researchers hope that it might be able to produce views of super-sized gas giant planets. If it succeeds, more powerful models that can hone in on smaller Earth-like planets such as the Kepler planets could conceivably follow.
The Kepler mission is expected to continue at least through 2016. Other NASA missions may pick up where it leaves off after that and, like the adaptive optics systems, could make possible more detailed views of the newly discovered planets. Among these are the Transiting Exoplanet Survey Satellite (TESS) mission, which is scheduled to launch in 2017. It will scan sectors of the nearby Milky Way for approximately 2 million stars, and it might be able to locate small planets even closer to Earth than the Kepler planets.
There is also the James Webb Space Telescope (JWST), which NASA is building with collaboration from 16 partner countries, including France, who will launch the completed JWST into orbit atop an Ariane rocket system. Its high-resolution cameras could, researchers hope, pick up details of habitable exoplanets, in addition to investigating the farthest limits of the visible universe and the formation of the earliest galaxies.
Of course, there is no telling how many more exoplanets might await discovery in the Milky Way’s more remote corners, much less in other galaxies. The Milky Way alone could be home to some 100 billion to 400 billion exoplanets, if astronomers’ projects are accurate, and many billions more galaxies lie beyond.