NASA’s Kepler mission to discover exoplanets has recently reported over 1,000 planets beyond our solar system. Of these, only 10 are Earth-sized planets orbiting in its parent star’s habitable zone. Within this selection, Kepler-22b is the smallest of these 10 planets. On December 5, 2011, NASA’s Kepler mission confirmed Kepler-22b to be the mission’s first potentially habitable planet discovered. This is because it orbits in its sun’s habitable zone, the area around a star where liquid water can exist.
A diagram of Kepler-22b’s orbit compared to the inner solar system. Source: Wikipedia
The planet is from the constellation Cygnus, a whopping 600 light-years from Earth. So any goals of reaching this planet are, unfortunately, extremely unrealistic. Compared to Earth, it’s radius is roughly 2.4 times the size of our planet. Despite its relatively similar size to Earth, the composition of the planet (solid, liquid, gas) is still unknown. The orbit of the planet is estimated to be around 290 days, not that different from Earth. Kepler-22, the host star, is a bit smaller and cooler than our sun, but it is of the same classification as the Sun, a G-Type star. According to NASA scientist Doug Hudgins, “This is a major milestone in discovering Earth’s twin”.
Artists rendering of Kepler-22b. Source: Wikipedia
Planets are discovered with the Kepler spacecraft by studying stars and looking for transits of planets. That is, when a planet crosses in front of its parent star, in this case Kepler-22. Kepler requires three separate transits of a planet before it can be verified as a possible planet. 22b’s first transit came only three days after the mission began, and the final transit came in the holiday season of 2010. Further research is then done by ground based telescopes and the Spitzer Space Telescope.
Overall, the amount of exoplanets discovered as of December 2011 had increased by 200 (140%) since February of the same year and more planets are being discovered all the time. Who knows how many planets have been found since.
