Astronomers have discovered a pair of neighboring planets with dissimilar densities orbiting very close to each other. The planets are too close to their star to be in the so-called "habitable zone," the region in a star system where liquid water might exist on the surface, but they have the closest orbits between two planets ever confirmed. The findings appear today in the journal Science.
The research team, led by Josh Carter, a Hubble fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and Eric Agol, a professor of astronomy at the University of Washington in Seattle, used data from NASA's Kepler space telescope, which measures dips in the brightness of more than 150,000 stars, to search for planets.
The inner planet, Kepler-36b, orbits its host star every 13.8 days, and the outer planet, Kepler-36c, every 16.2 days. On their closest approach, the neighboring duo comes within about 1.2 million miles (1.9 million kilometers) of each other. This is only five times the Earth-moon distance and about 20 times closer to each other than any two planets in our solar system.
Kepler-36b is a rocky world measuring 1.5 times the radius, and 4.5 times the mass, of Earth. Kepler-36c is a gaseous giant measuring 3.7 times the radius, and eight times the mass, of Earth. The planetary odd couple orbits a star slightly hotter, and a couple of billion years older, than our sun. The planets are located 1,200 light-years from Earth.
Image credit: Harvard-Smithsonian Center for Astrophysics
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