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Four worlds 133 light-years away orbiting a young star. (Jason Wang/Northwestern University) ********************************************************* A new video shared on YouTube is one of the most amazing things we've ever seen in planetary science. The video shows four dots of light moving in partial concentric circles around a black disk at their center. What you're actually looking at is a planetary system. The four dots are exoplanets, with the black disk obscuring their star, 133.3 light-years away from Earth. The partial circles are their orbital motions, a time-lapse compiled from 12 years of observations. The star is HR8799, and in 2008 its...

1. The Earthiest Kepler-78b is most similar to Earth in mass, diameter and composition; it could be made of rock with an iron core. But it’s no Earth analog, whizzing around its star in 8.5 hours, with temperatures exceeding 2,000° Celsius (SN Online: 10/30/13). 2. The wettest HR 8799c’s atmosphere lacks methane, which could signal life, but does have water and carbon monoxide (SN: 4/6/13, p. 5). Water has also been found in the atmospheres of WASP-17b, HD209458b, WASP-12b, WASP-19b and XO-1b. 3. The rogue Planetary candidate PSO J318.5-22 has no parent star. The object is roughly six times the...