NASA's Spitzer Space Telescope revealed a system of seven Earth-size planets around a cold small star. This system is called TRAPPIST-1. Three of these planets are located in the habitable zone, the area around the main star where a rocky planet is most likely to have liquid water. Most of these planets orbit their sun closer than Mucery orbits our sun and they all are so close together if you where standing on one of the planets you could see at least three other planets. Astronomers are thinking that the planets are tidally locked to their sun which means that the same side of the planet is always facing the sun.
NASA's Kepler mission confirmed the first near-Earth-size planet in the “habitable zone” around a sun very similar to our star. There are other planets that are in the habitable zone but they are all 40 percent larger than earth. They called this planet Kepler-186f and predict that the planet is very rocky. Also this planet is very close to the size of earth. "Finding a habitable zone planet comparable to Earth in size is a major step forward" said Elisa Q. Kepler-186f orbits its star once every 130-days and receives one-third the energy from its star that Earth gets from the sun, placing it nearer the outer edge of the habitable zone.
Kepler-10c was discovered in 2011 by NASA's Kepler space telescope. The planet has a diameter slightly more than double that of Earth's. Its size made astronomers think it was a smaller version of the gassy planet Neptune, which is four times the diameter of Earth. Xavier D. found out that Kepler-10c is actually seventeen times as heavy as Earth almost the same mass as Neptune. They are thinking this planet is a very dense, rocky world. Kepler-10c was put in the category of "mega-Earth", because it couldn't be in a class called super-earth because super-earths are bigger than earth but much lighter than Neptune. It is probably made from the same materials as Earth with water, silicates and iron. But in different proportions, says Xavier D.
APA citations
APA:Northon, K. (2017, February 22). NASA Telescope Reveals Record-Breaking Exoplanet Discovery. Retrieved April 19, 2017, from https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around/
APA:Culler, J. (2015, March 24). Kepler Finds 1st Earth-Size Planet In 'Habitable Zone' of Another Star. Retrieved April 19, 2017, from https://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star
APA:Heaviest Earth-like planet makes its presence felt. (2014). New Scientist, 222(2972), 17.