Rice University Assistant Professor Christopher Johns-Krull, one of the study's authors, said the finding sheds light on how Earth-like planets might form.

"Precisely how and when planets form is an open question," said Johns-Krull. "We believe the disk-shaped clouds of dust around newly formed stars condense, forming microscopic grains of sand that eventually go on to become pebbles, boulders and whole planets."

In previous studies, astronomers used infrared heat signals to identify microscopic dust particles around distant stars, but the method can't determine how big they become, and whether the particles orbit near the star or at a greater distance.

In the new study, Johns-Krull and co-authors in the United States, Germany and Uzbekistan used reflected light from the sand to confirm the Earth-like orbit of grainy particles around a pair of stars called KH-15D in the constellation Monoceros. The stars are about 2,400 light years from Earth in the Cone Nebula, and they are only about 3 million years old, compared to the sun's 4.5 billion years, the researchers said.

The study appears in the online edition of the journal Nature.