Astronomers say 1% to 3% of white dwarves have evidence of asteroids and rocky planets orbiting around them. This suggests that in the distant past they used to be like our own solar system.

White dwarves are what stars like the Sun become at the end of their lives. Their surface consists mostly of hydrogen and helium with a small addition of heavier elements like calcium.

The observation by an international team via NASA’s Spitzer Space Telescope revealed that some of the dwarves are polluted by a gradual rain of orbiting dust, reports the British Royal Astronomical Society. It radiates in the infrared range of the spectrum, which can be picked up by the telescope.

The team believes the dust is produced by asteroids similar to the dwarf planet Ceres in the Sun’s asteroid belt that was ripped apart by tidal forces. To come close enough to the star for it to happen, they must be perturbed from regular orbits by some external force. The force is likely to be the gravitation of bigger planets not observed by the instruments the scientists have now.

At least one to three small stars are contaminated in this way, the data suggests. A white dwarf is the final destination of the main sequence of star evolution, and the Sun will eventually become one. This is good news for those eager to find Earth-like planets around other stars. There can be as many as five million in our own galaxy.