Planets rich in carbon -- the main element in life -- may lack the oceans of water necessary to kick-start life's creation, NASA-funded research suggests.

Planetary systems rich in carbon are likely to lack the icy water reservoirs thought to supply planets with oceans, as happened with Earth, scientists suggest.

"The building blocks that went into making our oceans are the icy asteroids and comets," Torrence Johnson of NASA's Jet Propulsion Laboratory in Pasadena, Calif, said.

"If we keep track of these building blocks, we find that planets around carbon-rich stars come up dry," he said.

The sun is a carbon-poor star, and as a result Earth is made up largely of silicates, not carbon.

Stars with much more carbon than the sun are predicted to make planets chock full of carbon, scientists said, and the extra carbon in a planetary system developing around such stars would snag most of the available oxygen, preventing it from forming water, Johnson and his colleagues said.

"It's ironic that if carbon, the main element of life, becomes too abundant, it will steal away the oxygen that would have made water, the solvent essential to life as we know it," researcher Jonathan Lunine of Cornell University said.