The Sun and the planet Jupiter are the heaviest objects in the solar system. But there’s a huge gap in their masses – the Sun is more than a thousand times heavier.

There’s a class of objects between those masses. Known as brown dwarfs, they’re much heavier than Jupiter, but no more than seven or eight percent of the Sun’s mass.

A brown dwarf probably forms in the same way as a star – from the collapse of a cloud of gas and dust. The heat of that collapse makes the brown dwarf shine. But a brown dwarf isn’t massive enough to “fuse” hydrogen atoms in its core to make helium – the power source of most true stars. It may briefly fuse a heavy form of hydrogen, but that doesn’t produce nearly as much energy. So brown dwarfs are also known as “failed stars.”

The surface of a brown dwarf can be so cool that clouds can form in its upper layers, making it look like a giant planet, such as Jupiter. And despite the name, brown dwarfs aren’t really brown. Their color can range from dull orange or red to dark purple to black – a result of the surface temperature and chemistry.

The closest brown dwarfs form a binary known as Luhman 16. The system is six and a half light-years away – closer than only two star systems. Even so, it took a special space telescope to discover the pair – faint “missing links” between true stars and giant planets.

Script by Damond Benningfield