Using the Keck I telescope on Mauna Kea in Hawaii, Beth Klein of UCLA and colleagues did spectroscopic observations of two white dwarfs. One candidate, called PG1225-079, has an atmosphere containing magnesium, iron and nickel in ratios that resemble Earth's chemical recipe.
The other target, HS2253+8023, contains more than 85 percent oxygen, magnesium, silicon and iron. These would have only condensed around a body that was born at high temperatures, very close to the star, such as Earth was 4.5 billion years ago.
The researchers report that they now know of four heavily polluted white dwarfs that swallowed objects which formed within a close warm zone around their star, analogous to the inner planetary region of our solar system.
"It is clear that extrasolar planetary systems produce rocky bodies that are compositionally similar to terrestrial planets in our own solar system. Earth-like planets apparently do form elsewhere in the galaxy," Klein's group write in their Astrophysical Journal paper.