The white dwarf stars, in a star cluster, are being "polluted" by debris from asteroid-like objects falling onto them, suggesting rocky planet assembly is common in such clusters, Jay Farihi of the University of Cambridge said.
Seeing evidence of asteroids points to the possibility of Earth-sized planets in the same system, as asteroids are the building blocks of major planets, the researchers said.
Using spectroscopic observations from the Hubble space telescope, the researchers identified silicon in the atmospheres of the two white dwarfs, spacetelescope.org reported Thursday.
"We have identified chemical evidence for the building blocks of rocky planets," Farihi said. "When these stars were born, they built planets, and there's a good chance that they currently retain some of them.
"The signs of rocky debris we are seeing are evidence of this -- it is at least as rocky as the most primitive terrestrial bodies in our Solar System."
Hubble also detected low levels of carbon, another sign of the rocky nature of the debris because astronomers say they expect carbon levels should be very low in rocky, Earth-like material.
"Based on the silicon-to-carbon ratio in our study, for example, we can actually say that this material is basically Earth-like," Farihi said.