This year was a big one for exoplanets. Astronomers added a slew of candidates to the thousands-long list of potential exoplanets and confirmed fifteen off that list to be the real thing. But we still haven’t found Earth's twin, which is still the elusive holy grail of exoplanet hunters. But that might not be the case this time next year. Will 2013 be the year of a twin Earth?
We’ve been looking for another Earth for a long time. Before scientists knew that stars were distant suns playing host to their own planetary systems, they looked for similarities with our planetary neighbors. Victorian scientists referred to Venus as Earth twin for its similar size and distance from the Sun. Of course, Venus is roasting hot, rotates backwards, and has a day as long as its year--the planets are fraternal twins at best.
The Earth’s-twin search took on a new dimension in 1995 when astronomers started finding distant sun-like stars with planetary systems. The first exoplanets they found were so-called hot Jupiters. These failed stars turned massive planets are easy to see as they transit their host stars. The star’s light dims when the planets passes between it and a telescope; this is how NASA’s Kepler space telescope has found so many exoplanet candidates.
As detection methods and instruments improved, smaller planets came into view. Astronomers started finding rocky terrestrial bodies. Some are similar in size to the Earth, some have water, and others are in the right orbit to have liquid water exist on the surface. But still, we haven’t found a twin. Even the most Earth-like planets are either too big or orbit too close to their stars to have right conditions for life as we know it on Earth.
Exoplanet hunting astronomers are hoping their luck will change in 2013. So far, just 100 of the 2,300 candidate planets Kepler has found have been confirmed as true exoplanets. Astronomers hope to confirm another 80 percent of the current list of candidates as real planets, hopefully finding a twin Earth in the mix.