The notion of a dark planet far from any star sounds like a story to me, perhaps a story of astronauts journeying to a giant planet somewhere between earth and the nearest star and finding moons with the frozen remnants of an alien outpost.
The new work was done using a method known as gravitational microlensing, which is more sensitive to planets farther out. It relies on the ability of the gravitational field of a massive object — in this case a planet and its star — to bend light and act as a magnifying lens, as predicted by Einstein’s general theory of relativity.
Astronomers from two groups — Microlensing Observations in Astrophysics, based in New Zealand and Japan, and the Optical Gravitational Lensing Experiment, based in Poland and Chile — monitor the light from a vast field of background stars, looking for brief blips of increased brightness caused by a planet and its host star passing in the foreground.
The group recorded 10 such events consistent with being caused by planet-size objects but did not detect the corresponding blips from these planets’ host stars, suggesting either that they did not belong to any star, having been ejected by gravitational pinball games earlier in their lives, or that they were very distant.