Astronomers find planets so close they 'see' each other in night sky

Unbelievable but true: Astronomers have discovered two planets so close to each other each can be seen in the other's night sky, just like a moon. Researchers said the two planets are just 1.9 million km of each other, according to an article posted on Space.com. "This is unprecedented.... They are as different in density as Earth and Saturn (the highest and lowest density planets in our solar system), yet they are (20) times closer than any pair of planets in our solar system," Space.com quoted co-lead author Eric Agol of the University of Washington as saying. He was referring to planets Kepler-36b and c, which are 1,200 light-years from Earth and which researchers described as an unprecedented find. The researchers published their results June 21 in the journal Science. Space.com said Kepler-36b appears to be a rocky "super-Earth" 4.5 times as massive as our planet, while Kepler-36c is a gaseous, Neptune-size world about eight times as massive as Earth. Both planets meet up every 97 days in a conjunction that would make each "dramatically visible in the other's sky," it added. At their closest approach, the two planets are separated by five times the distance between the Earth and the moon. Researchers admitted it may be hard to explain using current theories how such different bodies ended up in such similar orbits. “These two worlds are having close encounters,” said co-lead author Josh Carter, of the Harvard-Smithsonian Center for Astrophysics. 'Planet-rise' Every 97 days, Kepler-36b and c experience a conjunction that brings them within 1.9 million km of each other, or about five times the Earth-Moon distance. "Planet c would appear roughly 2.5 times the size of the full moon when viewed from the surface of planet b. Conversely, planet b would appear about the size of the full moon on planet c," Carter said. He speculated planet c may appear slightly more purple that Neptune, due to absorption of red and yellow by sodium and potassium. "There could also be a slight brown tint owing to hazes of photo-disassociated methane," he said. Such dramatic vistas could well be around for many years to come, for the orbits of Kepler-36b and c appear unlikely to change anytime soon, Space.com quoted the researchers as saying. "We are addressing this in a follow-up paper, but the short answer is that yes, these do appear to be stable on a long timescale," Agol said. Kepler-36 system The two planets in the Kepler-36 system, located in the constellation Cygnus (The Swan), were detected by NASA's Kepler Space Telescope. Since its March 2009 launch, Kepler has flagged more than 2,300 potential alien planets though only a small fraction have been confirmed to date. But researchers said both planets are likely too hot to support life as we know it, with Kepler-36b probably sporting lava flows on its surface. They said both planets orbit roughly three times closer to their host star, known as Kepler-36a, than Mercury does to our Sun. Also, they said Kepler-36a is likely a bit hotter than our star. Researchers believe Kepler-36c, about 3.7 times wider than Earth, likely has a rocky core surrounded by a substantial atmosphere filled with hydrogen and helium. They believe Kepler-36b is just 1.5 times wider than our planet. "Iron likely constitutes about 30 percent of its mass, water around 15 percent and atmospheric hydrogen and helium less than 1 percent," Space.com quoted researchers as saying. Despite their different size and makeup, both planets travel on similar paths around their star. Kepler-36c orbits once every 16 days, at an average distance of 19 million km. Kepler-36b orbits each 14 days and sits about 18 million km from the star. Researchers believe Kepler-36b probably formed relatively close to the star, while Kepler-36c likely took shape farther out. Refinements Researchers said the Kepler-36 system may force some refinements in the way astronomers theorize large-scale migrations that can bring initially far-flung planets much closer together. "These models rely on assumptions that will likely have to be 'tweaked' or refined to account for both b and c's proximity and compositional differences. The existence of Kepler-36 may help clarify or invalidate these assumptions," Carter said. — LBG, GMA News