EARTH-sized planets that could harbour life are floating freely between the stars, according to new research.
These wandering worlds are known as "free floating", "rogue" or "orphan" planets and have just been detected for the first time.
They cross the Milky Way without companion planets or even a star - and there are probably billions out there.
These worlds are likely to be shrouded in darkness, but this doesn't mean organisms couldn't survive on the "rogue planets".
Heat from the planet's formation and decaying radioactive elements in the rock would still make them habitable.
Life could also survive around hydrothermal vents, which are holes in a planet's crust.
Planets that have no stars were only identified as a new class in 2011 - but they tended to be gas giants rather than rocky worlds like Mars and Earth.
Now Polish astronomers have carried out a second survey of the Milky Way's vast central "bulge" that was six times larger than any other study.
This indicated the existence of free floating rocky planets the size of Earth - and "super-Earths" that would be two to ten times as big.
Some scientists have suggested they could have lakes, oceans and hydrothermal vents like those on Earth where life thrives.
Prof Andrzej Udalski and colleagues used a technique called "gravitational micro-lensing" where light gets bent as it passes close to a large object - such as an "orphan planet".
The planet's gravity warps the space around it - making the area act like a giant magnifying glass.
If this "magnifying glass" passes in front of a star that is already being watched by a telescope on Earth the star will brighten for a short period of time.
First author Przemek Mroz, a PhD student in Prof Udalski's lab at Warsaw University Observatory, said: "We detected a few possible ultrashort-timescale events - less than half a day - which may indicate the existence of Earth-mass and super-Earth-mass free-floating planets, as predicted by planet-formation theories."
"Future space-based missions - like WFIRST and Euclid - will enable the exploration of these short events in more detail."
Euclid is a European Space Agency telescope due to be launched in 2020 to investigate the "dark universe".
The Wide Field Infrared Survey Telescope (WFIRST) is expected to be launched by NASA in 2025 to study the atmosphere of exoplanets - worlds beyond our solar system.
Thousands have been detected in the past two decades - but very few have been deemed potential candidates for life.
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The study published in Nature said theories have predicted free-floating planets that were ejected from their parent systems billions of years ago
Previous research has suggested they may be warm enough to support life due to the greenhouse effect of large amounts of hydrogen in their very thick atmospheres.
Free-floating Earth-sized planets could have habitable surface temperatures because without a star they don't have a mechanism to remove the atomic hydrogen from their atmosphere - effectively turning it into a greenhouse gas.
Scientists also suspect they could harbour life thanks to the heat produced by the decay of radioactive elements in their interior.
Some experts believe a rogue star system could smash into our planet and wipe out humanity.
Others believe a rogue planet is lurking at the edge of our solar system.