New research shows life in the early Universe might have been born on "carbon planets," a finding that strengthens the argument that life, including intelligent life, does indeed exist somewhere out there.

A Harvard University study argues life might have evolved on carbon planets made up of graphite, carbides and diamond despite the absence of carbon and oxygen that are necessary to create life as we know it. In contrast, the Earth consists of silicate rocks and an iron core plus abundant water.

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The study said the primordial Universe consisted mainly of hydrogen and helium. Only after the first stars exploded into supernovae and seeded the second generation with carbon and oxygen did planet formation and life become possible.

The study noted that young planetary systems lacking heavy chemical elements but relatively rich in carbon could form worlds made of graphite, carbides and diamond rather than Earth-like silicate rocks.

The research suggests the first potentially habitable worlds to form might have been very different but were hospitable to life. It noted that astronomers might find these "diamond planets" by searching for a rare class of stars known as "Carbon-Enhanced Metal-Poor" stars or CEMP stars.

"This work shows that even stars with a tiny fraction of the carbon in our solar system can host planets," said Natalie Mashian, study lead author and Harvard University graduate student.

"We have good reason to believe that alien life will be carbon-based, like life on Earth, so this also bodes well for the possibility of life in the early Universe," she adds.

CEMP stars contain only one hundred-thousandth as much iron as our Sun, meaning they formed before interstellar space was widely seeded with heavy elements. These very old stars have more carbon than might be expected given their age.

This abundance of carbon would influence planet formation since fluffy carbon dust grains can clump together to form tar-black worlds. These carbon planets would be difficult to tell apart from more Earth-like planets when viewed from the Earth or from near Earth orbits.

The masses and physical sizes of these carbon planets would be similar to the Earth's. Astronomers will have to examine the atmospheres of carbon planets for signs of their true nature. Gases like carbon monoxide and methane will likely encase these bizarre worlds.

"These stars are fossils from the young universe," said Avi Loeb of the Harvard-Smithsonian Center for Astrophysics and Mashian's Ph.D advisor.

"By studying them, we can look at how planets, and possibly life in the universe, got started."

Mashian and Loeb insist a dedicated search for planets around CEMP stars can be done using the transit technique.

"This is a practical method for finding out how early planets may have formed in the infant universe," says Loeb. "We'll never know if they exist unless we look," said Mashian.

Tagscarbon planets, diamond planets, Harvard University, Carbon-Enhanced Metal-Poor stars, CEMP stars