Kepler 186F lit up space nerds' imaginations four years ago when NASA announced it was the first potentially habitable, Earth-size planet confirmed beyond our solar system. The 500-light-year-away exoplanet is the first Earth-size planet identified beyond the Solar System, orbiting a star in its habitable zone. Scientists from NASA announced on April 17 that they have discovered the first-ever Earth-size planet apparently able to sustain life similar to humans outside the solar system.
For the first time, scientists have discovered an alien planet as large as Earth, within its host star's habitable zone, Earth's cousin, which may have just the liquid water and right conditions to support life within the habitable zone of its host star, the planets home planet. Using data from Kepler, astronomers from the University of California, Berkeley, and the University of Hawaii, estimate tens of billions of potentially habitable, Earth-size planets in our galaxy. In 2011, the institutions announced Kepler had observed five planets about Earth's size, all within the habitable zone.
The Kepler-186 system hosts Kepler-186f, the first confirmed Earth-size planet orbiting a distant star in the habitable zone--the range from a star at which liquid water can pool on an orbiting planet's surface. Before Kepler-186fs discovery, the record-holder for most Earth-like planets went to Kepler-62f, which is 40% larger than Earth's size and orbits within its star's habitable zone. The discovery confirmed the existence of planets as large as Earth within the star's habitable zone, and it signals a major step toward finding Earth-like worlds.
Kepler-186f, the planet orbits its star in its habitable zone -- meaning that its sun could be keeping it just the right temperature to allow liquid water on its surface. Although its host star is fainter than the sun is to Earth, and the planet is a bit larger than Earth, the placement of the alien world, along with its size, suggests that Kepler-186f may harbor water on its surface, scientists said. Kepler-186f has a diameter just 10 percent larger than our sun, so, like our planet, it is likely made up of rocks, iron, ice, and water - the kind of environment that we think is best for the evolution of life.
If you stood on the exoplanet's surface, the planet Kepler-186f would look roughly 30 percent larger than the planet looks from Earth, but Kepler-186f would get a little less light from its star than Earth does from the sun. If the planet Kepler-186f had a similar atmosphere to Earth, its sunrises and sunsets would have been enhanced than Earth's, Quintana said, because overall, the less blue light would come from its star. The planet Kepler-186f might be visible by the eye for short periods, like at sunset, and it would appear to be a bright star, like what Venus looks from Earth, Quintana said.
The star is as bright as it is during the highest point in its day, according to NASA, when standing on an exoplanet 500 light-years away, and would appear just as bright as the sun is right before sunset on our planet. The newly discovered planet, Kepler-186f was first discovered by NASA's Kepler Space Telescope and orbits around its host star. Scientists believe that Kepler-186f - the outermost of the five planets found orbiting the star Kepler-186 - is orbiting 32.5 million miles (52.4 million kilometers) away, theoretically inside a habitable zone for the red dwarf.
Kepler-186 hosts at least five planets, with four -- Kepler-186b, Kepler-186c, Kepler-186d, and Kepler-186e -- orbiting in very short periods of time and are extremely hot, and a fifth, called Kepler-186f, is at the center of the habitable zone of Kepler-186. The Kepler-186 system is also home to four inner planets, seen lined up in orbits around the host star, which is one-half the size and mass of the Sun. In this case, the name of a planet is just the star (Kepler-186, the 186th star found by NASA's Kepler Space Telescope to have a planet orbiting it), and the letter indicating how far away from the star a planet is (there is never an a, so the inner four planets of this system are b, c, d, and e).
NASA's Kepler space telescope discovered this one using a transit technique, together with four other planets orbiting far closer to Kepler-186, the red dwarf (all moderately larger than Earth). It orbits far closer to its host star than Earth, inside Mercury's orbit in our own Solar System. Even two years after Kepler 186F was announced, it still seems like a plausible candidate for being potentially habitable: it comfortably orbits at the outer edge of the sun's habitable zone, and given its measured radius, it seems probable that this exoplanet has a rocky composition compared with other planets of similar sizes.
As such, it highlights the diversity of habitable planets, expanding the definition beyond those that orbit stars like Earth. One goal of NASA's Kepler mission, launched March 7, 2009, as well as an important driving force behind its design, was to discover the transits of Earth-size planets in Earth-like orbits around sun-like stars -- the kinds of worlds one might expect to potentially be habitable, abodes of life as we know it. The discovery marks a milestone in the search for planets that are not only Earth-size but actually like the planet, said Doug Hudgins, NASA's project scientist on the Kepler mission in Washington.
For purposes of computing how frequently potentially habitable, Earth-like planets appear in the Milky Way, the team focused on stars from the final data set from Kepler's now-defunct space telescope, which are similar in age (ca. Around the time NASA's Kepler Space Telescope was retired, the international astronomers used the software to go back through data for a specific star--which had already been found to host four nearby planets--and discovered that it would miss one. Based on how many planets the Kepler mission found, scientists now estimate that the Milky Way may contain more planets than stars (the latest estimates suggest 100 billion to 400 billion stars).
Suppose Kepler 186f is a rocky planet with an inventory of volatiles roughly similar to Earth. In that case, it seems it might be habitable, provided that it has sufficient levels of geologic activity to support the carbonate-silicate cycle that acts as a planets thermostat, and unless there are any other obstacles to planet habitability associated with being located in a system with M-dwarfs.
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