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Earlier this week, the spacecraft, Kepler, discovered two exoplanets around the size of the earth – the first of their kind – orbiting a sun-like star. Named Kepler-20e and Kepler-20f, these exoplanets are a part of the star system, Kepler-20, which lies 950 light years away from Earth near the constellation, Lyra.
“This discovery demonstrates for the first time that Earth-size planets exist around other stars and that we are able to detect them,” says Dr. Francois Fressin, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
Launched in 2009, Kepler is a space telescope built and sent by NASA to detect Earth-like exoplanets (also known as extrasolar planets, which are planets that exist outside our solar system) orbiting stars in habitable zones. Its most recent, significant discovery occurred in early December, when it detected the Neptune-sized Kepler-22b, the first of its kind that has been seen orbiting in the “Goldilocks zone” and that might possibly have water and life.
Kepler took a step closer in accomplishing its mission when it detected Kepler-20, Kepler-20e, and Kepler-20f. Kepler-20 is similar to the sun, in that it is a G-type star. It is yellowish, though a bit smaller and cooler. The star contains five planets in total, all of which orbit it closer than Mercury orbits the sun. The three other planets are gas giants, which are about the size of Neptune, and each planet orbits alternating in size.
These newly discovered exoplanets are only Earth-like in their sizes and rocky composition. Kepler-20e orbits its star every 6.1 days, and its temperature is 1400° F. Its diameter, 6900 miles, is 0.87 times the diameter of the Earth’s. Kepler-20f has an orbit of 19.6 days. It has the temperature of 800° F, and it is 1.03 times Earth’s diameter, being 8,200 miles.
Because of their close orbits and high temperatures, these two exoplanets are not able to sustain water, let alone life. For them to have water and life, they have to lie in the “Goldilocks zone,” or the habitable zone, in which a planet cannot be too close or too far (hence, too hot or too cold) from the star it orbits.
Ever since its launch in 2009, Kepler has been detecting hundreds of exoplanets, many of which are not Earth-like, being hostile and sometimes lonely, not orbiting any stars. With its most recent detection of Kepler-22b and of Kepler-20′s two Earth-like planets, Kepler has reached a new landmark, not just in its journey, but in our knowledge of the various kinds of planets that exist in the observable universe.
“This could be an important milestone,” Dr. Fressin states. “I think 10 years, or maybe even 100 years, from now people will look back and ask when was the first Earth-sized planet found. It is very exciting.”