Kepler Spacecraft Discovers ‘Invisible Planet’
NASA’s Kepler spacecraft has spotted a planet that alternately runs late and early in its orbit because a second, “invisible” world is tugging on it. This is the first definite detection of a previously unknown planet using this method. No other technique could have found the unseen companion.
“It’s like having someone play a prank on you by ringing your doorbell and running away. You know someone was there, even if you don’t see them when you get outside,” she added.
Both the seen and unseen worlds orbit the Sun-like star Kepler-19, which is located 650 light-years from Earth in the constellation Lyra. The 12th-magnitude star is well placed for viewing by backyard telescopes on September evenings.
The first planet, Kepler-19b, transits its star every 9 days and 7 hours. It orbits the star at a distance of 8.4 million miles, where it is heated to a temperature of about 900 degrees Fahrenheit. Kepler-19b has a diameter of 18,000 miles, making it slightly more than twice the size of Earth. It may resemble a “mini-Neptune,” (image of Neptune above) however its mass and composition remain unknown.
If Kepler-19b were alone, each transit would follow the next like clockwork. Instead, the transits come up to five minutes early or five minutes late. Such transit timing variations show that another world’s gravity is pulling on Kepler-19b, alternately speeding it up or slowing it down.
Historically, the planet Neptune was discovered similarly. Astronomers tracking Uranus noticed that its orbit didn’t match predictions. They realized that a more distant planet might be nudging Uranus and calculated the expected location of the unseen world. Telescopes soon observed Neptune near its predicted position.
“This method holds great promise for finding planets that can’t be found otherwise,” stated Harvard astronomer and co-author David Charbonneau.
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