Few nighttime sights offer more drama than the full Moon rising over the horizon. Now imagine that instead of the Moon, a gas giant planet spanning three times more sky loomed over the molten landscape of a lava world. This alien vista exists in the newly discovered two-planet system of Kepler-36.
“These two worlds are having close encounters,” said Josh Carter, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics (CfA).
“They are the closest to each other of any planetary system we’ve found,” added co-author Eric Agol of the University of Washington.
Carter, Agol and their colleagues reported their discovery in the June 21 Science Express.
They spotted the planets in data from NASA’s Kepler spacecraft, which can detect a planet when it passes in front of—and briefly reduces the light coming from—its parent star.
The newfound system contains two planets circling a subgiant star much like the Sun except several billion years older. The inner world, Kepler-36b, is a rocky planet 1.5 times the size of Earth and weighing 4.5 times as much. It orbits about every 14 days at an average distance of less than 11 million miles.
The outer world, Kepler-36c, is a gaseous planet 3.7 times the size of Earth and weighing 8 times as much. This “hot Neptune” orbits once each 16 days at a distance of 12 million miles.
The two planets experience a conjunction every 97 days on average. At that time, they are separated by less than 5 Earth-Moon distances. Since Kepler-36c is much larger than the Moon, it presents a spectacular view in its neighbor’s sky. Such close approaches stir up tremendous gravitational tides that squeeze and stretch both planets.
Researchers are struggling to understand how these two very different worlds ended up in such close orbits. Within our solar system, rocky planets reside close to the Sun while the gas giants remain distant.
Although Kepler-36 is the first planetary system found to experience such close encounters, it undoubtedly won’t be the last.
“We’re wondering how many more like this are out there,” said Agol.
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I’VE BEEN REFLECTING ON LAST WEEK’S COLUMN, where we noted that NASA’s Voyagers are “the two most distant active representatives of humanity.” That may be true, in a strictly “material” sense, but in a more ethereal sense, humanity has been actively sending out information about itself for at least 100 years now. I’m referring, of course, to radio waves.
Since about the time that the sinking Titanic radioed its SOS in 1912, radio (and later, TV) has been powerful enough to leak its messages outward toward the stars. Everything from the Titanic’s call for help to “I Love Lucy” to last night’s news report has been traveling at the speed of light in all directions, reaching by now all the stars within a radius of 100 light-years from Earth.
Just to mention the most familiar stars (out of hundreds within that radius), the “news” of our existence got to the nearest star, Alpha Centauri, by 1916; passed the brightest star, Sirius, by 1921; and won’t reach the North Star, Polaris, until the year 2446. Radio-frequency energy travels at the same speed as light—186,000 miles per second. I guess that’s pretty fast or pretty slow, depending on how you look at it!
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