Solar systems like our own may be forming around dim stars scattered all over the Milky Way. It’s possible that some of these systems could harbor planets with water and even life.
The likelihood of such a possibility has increased with the discovery of a disk of gas and dust orbiting a star only about 15 times more massive than Earth’s planetary neighbor, Jupiter. Such stars carry the undignified name “brown dwarfs,” because they never grow big enough to shine like a sun. But they could warm planets that form out of the encircling disk of stardust the way Earth and its neighbor planets formed around the sun.
“Such mini-solar systems are an exciting possibility, one that hasn’t been explored extensively because this is the first evidence for the building blocks of planets around such a small object,” says astronomer Kevin Luhman. He led a group of colleagues at the Harvard-Smithsonian Center for Astrophysics, who found OTS 44, a brown dwarf about 3,000 trillion miles away in the southern constellation Chamaeleon.
Brown dwarfs are objects 15-70 times more massive than Jupiter, which is 318 times as massive as Earth. OTS 44 is the smallest, coolest one ever detected with a preplanetary disk. It’s not all that much bigger than a planet itself. Brown dwarfs don’t shine like stars because they are not hot enough. But, at 3,600 degrees, this dwarf is large enough to comfortably warm planets that condense out of its disk.
Due to this brown dwarf’s small size and relatively cool temperature, any new, habitable planet would need to be much closer than the distance between Earth and its white hot sun, 93 million miles. Luhman estimates that liquid water and life could exist on a world 1 million to 4 million miles from OTS 44. The disk is wide enough to accommodate a planet at that distance.
Without starlike nuclear reactions to keep it going, the dwarf will gradually become cooler and dimmer. Any new planets would, at first, be too hot to sustain life, as we know it. But as time passed, these worlds would grow cooler and more hospitable. Given enough time in this zone, life might arise.
“It’s an intriguing possibility, but purely speculative,” Luhman admits. “However, finding a circumstellar disk around such a small brown dwarf certainly widens the possibilities for planet formation.”