
The world Kepler-19c, seen in the foreground of this artist’s conception, was discovered solely through its gravitational influence on the companion world Kepler-19b (the dot crossing the star’s face). Kepler-19b is slightly more than twice the diameter of Earth, and is probably a “mini-Neptune.” Nothing is known about Kepler-19c, other than that it exists.
http://www.space.com/12879-stealth-alien-planet-kepler-transit-timing-variation.html
http://kepler.nasa.gov/news/nasakeplernews/index.cfm?fuseaction=ShowNews&NewsID=148
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NASA's Kepler space telescope detected both alien planets, which are known as Kepler-19b and Kepler-19c. Kepler spotted 19b as it passed in front of, or transited, its host star. Researchers then inferred the existence of 19c after observing that 19b's transits periodically came a little later or earlier than expected. The gravity of 19c tugs on 19b, changing its orbit.
The discovery of Kepler-19c marks the first time this method — known as transit timing variation, or TTV — has robustly found an exoplanet, researchers said. But it almost certainly won't be the last.
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This is the first time an exosolar planet has been discovered by the observed effects on a known planet. The planet detected would not have been detected otherwise because it does not transit the star from our view.
Both worlds orbit the Sun-like star Kepler-19, which is located 650 light-years from Earth in the constellation Lyra. The first planet 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. Kepler-19b, transits its star every 9 days and 7 hours.