Did life begin on carbon planets in the early universe?

Carbon planets, quite unlike Earth, made of graphite, carbides and diamond, may have been the first to form and become the cradle of life in the universe, a study by Harvard University astronomers speculates.

“This work shows that even stars with a tiny fraction of the carbon in our solar system can host planets,” says lead author and graduate student Natalie Mashian.

“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.”

The early universe consisted mostly of hydrogen and helium, and lacked chemical elements like carbon and oxygen necessary for life as we know it. 

Only after the first stars exploded as supernovae and seeded the second generation did planet formation and life become possible, scientists have thought.

Mashian and Avi Loeb of the Harvard-Smithsonian Center for Astrophysics examined a particular class of old stars known as carbon-enhanced metal-poor stars, or CEMP stars.

These contain only 0.00001 as much iron as the Sun, and so must have formed before interstellar space had become seeded with heavy elements.

“These stars are fossils from the young universe,” says Loeb. “By studying them, we can look at how planets, and possibly life in the universe, got started.”

Although lacking in iron and other heavy elements compared to our Sun, CEMP stars have more carbon than would be expected given their age. 

This would influence the formation of planets made up carbon dust grains clumped together, possible with atmospheres of carbon monoxide and methane.

The next step for Mashian and Loeb is to try to prove these bodies exist.

They say we could find these jet black planets, by observing them transit across their CEMP stars.

“We’ll never know if they exist unless we look,” says Mashian.

This research has been accepted for publication in the Monthly Notices of the Royal Astronomical Society and is available online.