Planet or brown dwarf star around the star, CHXR 73?

What’s a Planet?

“I found a planet!” Caltech astronomer Mike Brown remembers exclaiming during a phone call he made to his wife early in 2005. Little did he know that he’d have to eat his words just 18 months later. Brown had found an outer–solar system object heavier than Pluto, so it seemed reasonable to call the object the tenth planet.

But last August, the International Astronomical Union approved the first formal definition of a planet since the Greeks coined the term some 2,000 years ago. Pluto, got the boot, and Brown’s proposed tenth planet, a body now called Eris, was disqualified.

The group of astronomers decided to call Pluto and Eris “dwarf planets”—a class that the scientists say is separate from the solar system’s eight official planets. That decision remains controversial, although many astronomers say that there’s merit in the demotion.

The gap in mass suggests that nature has two distinct ways to make an object that will orbit a star, Jayawardhana notes. One mechanism, the traditional planet-formation scenario, may dominate at low masses, while another, which tends to make brown dwarfs, may dominate at high masses.