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...for astronomer Scott Sheppard of the Carnegie Institution for Science in Washington DC, it was a much quieter affair. "It wasn't like there was a eureka moment," he says. "The evidence just built up slowly." He's a master of understatement. Ever since he and his collaborator Chad Trujillo of Northern Arizona University, first published their suspicions about the unseen planet in 2014, the evidence has only continued to grow. Yet when asked how convinced he is that the new world, which he calls Planet X (though many other astronomers call it Planet 9), is really out there, Sheppard will only...

The paper ... noted that a number of large, very remote objects share a similar orbital angle. That's suspicious if you're an astronomer expecting to see a random distribution of objects. The key orbital feature is known, rather obtusely, as the “argument of perihelion.” We're not shy of complicated orbital concepts (we try to toss around the phrase "obliquity of the ecliptic" whenever possible), but this one is not very easy to explain. "The argument of perihelion is the angle at which an object comes to perihelion with respect to the ecliptic plane," Sheppard said in an e-mail. Mike Brown,...

Asteroid 62412. Credit: Scott Sheppard Comets are often called “dirty snowballs” by astronomers. However, various investigative missions, such as Giotto and Deep Impact, revealed them to be blackened, cratered, and fractured. No ice fields, reflective crust, or watery clouds were observed. Indeed, the latest pictures from the Rosetta mission of 67P/Churyumov-Gerasimenko indicate that it is a mountain of rock in space. According to a recent press release, the Gemini Observatory’s image of asteroid 62412, located between Mars and Jupiter, is the first time that one of the Hygiea family of asteroids has exhibited a tail, and is only the...

Small objects could be rounded worlds, based on likely sizes, experts say. Three relatively bright space rocks recently found in Pluto's neighborhood may be new members of the dwarf planet family, astronomers say. The objects were discovered in a little studied section of the Kuiper belt, a region of the solar system that starts beyond the orbit of Neptune and extends 5.1 billion miles (8.2 billion kilometers) from the sun. Astronomer Scott Sheppard, of the Carnegie Institute of Washington, and colleagues found the bodies using the 1.3-meter Warsaw University Telescope at Las Campanas in Chile. The region of the Kuiper...