Giant super-earths made of diamond are possible

Dec 05, 2011 by Pam Frost Gorder
Iron, carbon, and oxygen subjected to intense temperatures and pressures form a pocket of iron oxide (bottom, center) and a darker pocket of diamond (bottom, right). Electron micrograph courtesy of Ohio State University.

(PhysOrg.com) -- A planet made of diamonds may sound lovely, but you wouldn't want to live there.

A new study suggests that some stars in the could harbor "carbon super-Earths" – giant terrestrial planets that contain up to 50 percent diamond.

But if they exist, those planets are likely devoid of life as we know it.

The finding comes from a laboratory experiment at Ohio State University, where researchers recreated the temperatures and pressures of Earth's lower mantle to study how form there.

The larger goal was to understand what happens to carbon inside planets in other solar systems, and whether solar systems that are rich in carbon could produce planets that are mostly made of diamond.

Wendy Panero, associate professor in the School of Earth Sciences at Ohio State, and doctoral student Cayman Unterborn used what they learned from the experiments to construct computer models of the minerals that form in planets composed with more carbon than Earth.

The result: "It's possible for planets that are as big as fifteen times the mass of the Earth to be half made of diamond," Unterborn said. He presented the study Tuesday at the American Geophysical Union meeting in San Francisco.

"Our results are striking, in that they suggest carbon-rich planets can form with a core and a mantle, just as Earth did," Panero added. "However, the cores would likely be very carbon-rich – much like steel – and the mantle would also be dominated by carbon, much in the form of diamond."

Earth's core is mostly iron, she explained, and the mantle mostly silica-based minerals, a result of the elements that were present in the dust cloud that formed into our solar system. Planets that form in carbon-rich solar systems would have to follow a different chemical recipe – with direct consequences for the potential for life.

Earth's hot interior results in geothermal energy, making our planet hospitable.

Diamonds transfer heat so readily, however, that a carbon super-Earth's interior would quickly freeze. That means no geothermal energy, no plate tectonics, and – ultimately – no magnetic field or atmosphere.

"We think a diamond planet must be a very cold, dark place," Panero said.

She and former graduate student Jason Kabbes subjected a tiny sample of iron, carbon, and oxygen to pressures of 65 gigapascals and temperatures of 2,400 Kelvin (close to 9.5 million pounds per square inch and 3,800 degrees Fahrenheit – conditions similar to the Earth's deep interior).

As they watched under the microscope, the oxygen bonded with the iron, creating iron oxide – a type of rust – and left behind pockets of pure carbon, which became diamond.

Based on the data from that test, the researchers made computer models of Earth's interior, and verified what geologists have long suspected – that a diamond-rich layer likely exists in Earth's lower mantle, just above the core.

That result wasn't surprising. But when they modeled what would happen when these results were applied to the composition of a carbon super-Earth, they found that the planet could become very large, with iron and carbon merged to form a kind of carbon steel in the core, and vast quantities of pure carbon in the mantle in the form of diamond.

The researchers discussed the implications for planetary science.

"To date, more than five hundred planets have been discovered outside of our , yet we know very little about their internal compositions," said Unterborn, who is an astronomer by training.

"We're looking at how volatile elements like hydrogen and interact inside the Earth, because when they bond with oxygen, you get atmospheres, you get oceans – you get life," Panero said. "The ultimate goal is to compile a suite of conditions that are necessary for an ocean to form on a planet."

This work contrasts with the recent discovery by an unrelated team of researchers who found a so-called "diamond planet" which is actually the remnant of a dead star in a binary system.

The Ohio State research suggests that true terrestrial diamond planets can form in our galaxy. Exactly how many such might be out there and their possible internal composition is an open question – one that Unterborn is pursuing with Ohio State astronomer Jennifer Johnson.

Explore further: Planets with oddball orbits like Mercury could host life

Related Stories

Carbonates make diamonds grow in the Earth's mantle

Apr 08, 2011

Diamonds that no-one ever sees can form deep in the Earth’s interior. This is due to the chemical conditions controlling the associated carbon cycle. Swiss researchers used laboratory experiments to show ...

Diamonds show depth extent of Earth's carbon cycle

Sep 15, 2011

Scientists have speculated for some time that the Earth's carbon cycle extends deep into the planet's interior, but until now there has been no direct evidence. The mantle–Earth's thickest layer –is ...

Under pressure: Ramp-compression smashes record

Nov 11, 2011

In the first university-based planetary science experiment at the National Ignition Facility (NIF), researchers have gradually compressed a diamond sample to a record pressure of 50 megabars (50 million times ...

Diamond is one tough cookie

Jan 26, 2010

(PhysOrg.com) -- Most people know that diamond is one of the hardest solids on Earth, so strong that it can easily cut through glass and steel. Surprisingly, very little is known about the strength of diamond ...

Exploring planets in distant space and deep interiors

Feb 14, 2009

In recent years researchers have found hundreds of new planets beyond our solar system, raising questions about the origins and properties of these exotic worlds—not to mention the possible presence of life. Speaking at ...

Recommended for you

The entropy of black holes

Sep 12, 2014

Yesterday I talked about black hole thermodynamics, specifically how you can write the laws of thermodynamics as laws about black holes. Central to the idea of thermodynamics is the property of entropy, which c ...

Modified theory of dark matter

Sep 12, 2014

Dark matter is an aspect of the universe we still don't fully understand. We have lots of evidence pointing to its existence (as I outlined in a series of posts a while back), and the best evidence we have point ...

Gaia discovers its first supernova

Sep 12, 2014

(Phys.org) —While scanning the sky to measure the positions and movements of stars in our Galaxy, Gaia has discovered its first stellar explosion in another galaxy far, far away.

User comments : 7

Adjust slider to filter visible comments by rank

Display comments: newest first

Nanobanano
3 / 5 (5) Dec 05, 2011
Diamonds transfer heat so readily, however, that a carbon super-Earth's interior would quickly freeze.


Yet another thing that can go catastrophically wrong with a planet.
antonima
not rated yet Dec 05, 2011
They had a planet like this in the game Escape Velocity - super-steel was one of the commodity goods for sale if I remember right x)
hyongx
3.7 / 5 (3) Dec 06, 2011
2000 years from now:

"Honey, I want the biggest diamond in the Universe!"

*sigh* "James, go fetch the space yacht. Make sure the planetary tractor beam is working. Go pick up that planet for me, would you."

"Oh you're just amazing, darling!!!"
Pirouette
1 / 5 (3) Dec 06, 2011
"To date, more than five hundred planets have been discovered outside of our solar system, yet we know very little about their internal compositions," said Unterborn, who is an astronomer by training."

Isn't it a bit premature to expect an ability to determine exact internal compositions of exoplanets discovered relatively recently at such distances through extrapolation and modeling? Even examining spectra cannot take the place of samples. Until probes are dispatched to said exoplanets, no definitive conclusion can be reached.
Callippo
3 / 5 (2) Dec 10, 2011
Hard life for extraterrestrial moles....
Cam_
2.3 / 5 (3) Dec 11, 2011
So later in the future would we be able to mine these diamonds? Could we obtain this Carbon-Steel?
Callippo
5 / 5 (1) Dec 11, 2011
We read these PopSci articles many years. Journalists know very well, the people are fascinated with these fairy tales. http://news.bbc.c...2919.stm