Diamond Planets Unlikely to Support Life

October 30, 2013

Silicate-based planet on the left covered with oceans versus barren, carbon-based planet on the right.

Silicate-based planet on the left covered with oceans versus barren, carbon-based planet on the right. Credit: NASA/JPL-Caltech

A recent study predicts that if there is such thing as diamond planet, it would be unlikely that it has water – the prerequisite for life as we know it.

It is fascinating how many things had to coincide in order to life on Earth to exist. For example, the size of our star, the position of Earth in our solar system, Jupiter protecting us from life-ending asteroids etc. A new research funded by NASA explored another factor – amount of carbon in the whole solar system.

Carbon is the basic building block of life as we know it. Life on Earth is carbon based. Although there is a possibility for life forms based on another element, on other planets as well as on our own, for the time being we haven't discovered any. It is peculiar then that our star, the Sun, has such low percentage of carbon.

The research presented in American Astronomical Society Division of Planetary Sciences meeting in Denver, USA, created a computer model to find out what would the chances for life be in a solar system rich with carbon.

Firstly, this would make diamond planets possible. Diamond planet or carbon planet is a planet that would be rich in carbon. With enough pressure, kilometers thick layer of diamonds could be present on such planet, hence the name. Earth and other rocky planets in our system are made mostly of silicon-oxygen compounds, making diamonds relatively rare and valuable. In recent years, diamond planets haven't been confirmed, but there are indications that they really exist.

Secondly, in such carbon-rich system there would be a lack of icy comets and asteroids. These are theorized to have given the Earth its oceans in the early stages of our planet's formation. In our carbon-poor system these rocks originated past a boundary called the snow line. In theoretical models in question, this snow line is nonexistent.

"There's no snow beyond the snow line," said Torrence Johnson, NASA's Jet Propulsion Laboratory in Pasadena, USA. This is because too much carbon would bind the oxygen, preventing it from forming water.

"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," says Jonathan Lunine, of Cornell University, Ithaca, USA. He was a collaborator on this study. "All rocky planets aren't created equal," he said. "So-called diamond planets the size of Earth, if they exist, will look totally alien to us: lifeless, ocean-less desert worlds."

So, it is a bit of a stretch and all theory here, but if the water on Earth originates from comets and asteroids and if planets covered with diamonds exist, the study shows they would be void of life, despite being in habitable zone around their stars. While these planets aren't exactly on top of the list of places where you would look for alien life, it brings us another step closer to answering the question "are we alone in the universe".

By current observations, there are 300 billion stars in our galaxy alone. So, there must be at least another planet with life on it, right? Well, more than half of the stars we see are actually systems of two or more stars where planets, if they existed, would have orbit not stable enough for the planet to remain in habitable zone. Habitable zone is the zone around the star(s) where water remains liquid. Then come other factors in play, like Jupiter-like gas giants that would have gravitational pull strong enough to keep asteroids away from the planet. It also doesn't help that at the time it is very hard for us to detect rocky planets that are usually smaller than gas giants. 

The list goes on. Crossing carbon-rich systems off the list could help us in narrowing down the potential systems where we should look for alien life, even if the theory is yet unconfirmed.



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