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For the first time since Pluto was demoted, the idea of a true ninth planet is edging from speculation toward something testable. Instead of restoring Pluto, researchers are closing in on a different, ...

Astronomers used a telescope in Hawaii to find a new object on the outer edges of our solar system, helping to fuel evidence of a long-standing theory about Planet Nine, or Planet X. For years, ...

Venture to the outer edges of the solar system where decades-long missions push the limits of human engineering. From ...

The five dwarf planets recognized by the International Astronomical Union are Pluto, Ceres, Eris, Haumea and Makemake—and these are pictured with 2017 OF201 in a telescope image. Dwarf planets: NASA / ...

The Outer planets have been vacillating indecisively, shifting in and out of new signs (Retrograding). However, the Outer ...

There may be a warp in the Kuiper Belt, possibly caused by “Planet Y” — a Mercury-to-Earth-sized world that orbits the sun way beyond the orbit of Neptune. Is there a mysterious “Planet Y” orbiting ...

Pluto's days, though they drag on a bit at around 153 hours, are nothing compared to its years. Pluto's orbit takes 248 Earth ...

What was discovered in Flagstaff, Arizona, and killed off in Prague? If you answered "Pluto's planethood," your grasp of the astronomical is excellent. Feb. 18 marks the 95th anniversary of the ...