for Earth-sized planets in an unlikely place– the atmospheres of a pair of
burned-out stars called white dwarfs.
These dead stars are located 150 light-years from Earth in a relatively young
star cluster, Hyades, in the constellation Taurus. The star cluster is only 625
million years old. The white dwarfs are being polluted by asteroid-like debris
falling onto them.
Hubble’s Cosmic Origins Spectrograph observed
silicon and only low levels of carbon in the white dwarfs’ atmospheres. Silicon
is a major ingredient of the rocky material that constitutes Earth and other
solid planets in our solar system. Carbon, which helps determine properties and
origin of planetary debris, generally is depleted or absent in rocky,
“We have identified chemical evidence for the building blocks of rocky
planets,” said Jay Farihi of the University of Cambridge in England. He is
lead author of a new study appearing in the Monthly Notices of the Royal
Astronomical Society. “When these stars were born, they built planets, and
there’s a good chance they currently retain some of them. The material we are
seeing is evidence of this. The debris is at least as rocky as the most
primitive terrestrial bodies in our solar system.”
This discovery suggests rocky planet assembly is common around stars, and it
offers insight into what will happen in our own solar system when our sun burns
out 5 billion years from now.
Farihi’s research suggests asteroids less than 100 miles (160 kilometers) wide
probably were torn apart by the white dwarfs’ strong gravitational forces.
Asteroids are thought to consist of the same materials that form terrestrial
planets, and seeing evidence of asteroids points to the possibility of
Earth-sized planets in the same system.
The pulverized material may have been pulled into a ring around the stars and
eventually funneled onto the dead stars. The silicon may have come from
asteroids that were shredded by the white dwarfs’ gravity when they veered too
close to the dead stars.