Exoplanets With Too Much Carbon Are Most Likely Waterless
October 26, 2013

Carbon-Rich Exoplanets May Lack Surface Water

redOrbit Staff & Wire Reports - Your Universe Online

Diamond planets and other worlds that are rich in carbon might be waterless, NASA researchers explained earlier this month at the 45th meeting of the American Astronomical Society Division of Planetary Sciences in Denver.

Torrence Johnson, a Senior Research Scientist at the Jet Propulsion Laboratory (JPL) in Pasadena, California, and his colleagues explain that since our sun is a carbon-poor star, the Earth is a planet that is made up primarily of silicates, not carbon.

Conversely, stars with more carbon than the sun are believed to create planets that are high in carbon content, perhaps even containing layers of diamond. By modeling the ingredients in these carbon-based systems, Johnson’s team has concluded that they likely lack the icy water reservoirs believed to supply worlds with oceans.

“The building blocks that went into making our oceans are the icy asteroids and comets,” explained Johnson, who spent decades studying the planets in our solar system as a member of the Galileo, Voyager and Cassini teams. “If we keep track of these building blocks, we find that planets around carbon-rich stars come up dry.”

The research team said that the extra carbon contained in developing star systems would capture oxygen, preventing the element from forming water. Cornell University professor Jonathan Lunine called it “ironic” that an over-abundance of carbon, which he refers to as “the main element of life,” could prevent water, “the solvent essential to life as we know it,” from forming.

Among the questions surrounding exoplanets (planets located beyond our own solar system) is whether or not they are habitable. As they attempt to answer that query, NASA scientists initially attempt to determine whether or not they are located at such a distance from their parent star that water can form on the surface – a region known as the “habitable zone.” The Kepler mission has discovered several worlds that have met this criteria.

However, even these so-called “Goldilocks” planets (so dubbed because they exist in a zone that is “just right” for the formation of surface water) could lack adequate amounts of water to actually wet the surface. To further examine that possibility, Johnson and his colleagues created planetary simulations based on measurements of our sun’s carbon-to-oxygen ratio.

“These models accurately predict how much water was locked up in the form of ice early in the history of our solar system, billions of years ago, before making its way to Earth,” NASA explained. “Comets and/or the parent bodies of asteroids are thought to have been the main water suppliers, though researchers still debate their roles.”

“Either way, the objects are said to have begun their journey from far beyond Earth, past a boundary called the ‘snow line,’ before impacting Earth and depositing water deep in the planet and on its surface,” the US space agency added. “When the researchers applied the planetary models to the carbon-rich stars, the water disappeared. ‘There's no snow beyond the snow line,’ said Johnson.”