CAPE CANAVERAL, Fla. -- Astronomers have discovered the earliest seeds of rocky planets forming in the gas around a baby sun-like star, providing a precious peek into the dawn of our own solar system.

A young sunlike star called HOPS 315 seems to host a swirling disk of gas giving rise to minerals that kick-start the planet formation process.

For the first time, international researchers have pinpointed the moment when planets began to form around a star beyond the ...