Diamond Oceans Possible on Uranus, Neptune

- Like ice on water, solid diamond floats on liquid diamond.

- The finding explains possible liquid diamond oceans on other planets.

- Diamond oceans may cause off-kilter planetary tilts.

Oceans of liquid diamond, filled with solid diamond icebergs, could be floating on Neptune and Uranus, according to a recent article in the journal Nature Physics.

The research, based on the first detailed measurements of the melting point of diamond, found diamond behaves like water during freezing and melting, with solid forms floating atop liquid forms. The surprising revelation gives scientists a new understanding about diamonds and some of the most distant planets in our solar system.

"Diamond is a relatively common material on Earth, but its melting point has never been measured," said J. H. Eggert of Lawrence Livermore National Laboratory in Livermore, California. "You can't just raise the temperature and have it melt, you have to also go to high pressures, which makes it very difficult to measure the temperature."

Other groups, notably scientists from Sandia National Laboratories, successfully melted diamond years ago, but they were unable to measure the pressure and temperature at which the diamond melted.

Diamond is an incredibly hard material. That alone makes it difficult to melt. But diamond has another quality that makes it even harder to measure its melting point. Diamond doesn't like to stay diamond when it gets hot. When diamond is heated to extreme temperatures it physically changes, from diamond to graphite.

The graphite, and not the diamond, then melts into a liquid. The trick for the scientists was to heat the diamond up while simultaneously stopping it from transforming into graphite.

Eggert and his colleagues took a small, natural, clear diamond, about a tenth of a carat by weight and half a millimeter thick, and blasted it with lasers at ultrahigh pressures like those found on gas giants like Neptune and Uranus.

The scientists liquefied the diamond at pressures 40 million times greater than what a person feels when standing at sea level on Earth. From there they slowly reduced the temperature and pressure.

When the pressure dropped to about 11 million times the atmospheric pressure at sea level on Earth and the temperature dropped to about 50,000 degrees, solid chunks of diamond began to appear. The pressure kept dropping, but the temperature of the diamond remained the same, with more and more chunks of diamond forming.

Then the diamond did something unexpected. The chunks of diamond didn't sink. They floated. Microscopic diamond ice burgs floated in a tiny sea of liquid diamond. The diamond was behaving like water.

With most materials, the solid state is more dense than the liquid state. Water is an exception to that rule; when water freezes, the resulting ice is actually less dense than the surrounding water, which is why the ice floats and fish can survive a Minnesota winter.

An ocean of diamond could help explain the orientation of Uranus' and Neptune's magnetic field as well, said Eggert. Roughly speaking, the Earth's magnetic poles match up with the geographic poles. The magnetic and geographic poles on Uranus and Neptune do not match up; in fact, they can be up to 60 degrees off of the north-south axis.

If Earth's magnetic field were that far off it would place the magnetic north pole in Texas instead of off a Canadian island. A swirling ocean of liquid diamond could be responsible for the discrepancy.

Up to 10 percent of Uranus and Neptune is estimated to be made from carbon. A huge ocean of liquid diamond in the right place could deflect or tilt the magnetic field out of alignment with the rotation of the planet.

The idea that there are oceans of liquid diamond on Neptune and Uranus is not a new idea, said Tom Duffy, a planetary scientist at Princeton University.

The new Nature Physics article makes diamond oceans "look more and more plausible," said Duffy.

More research on the composition of Neptune and Uranus is needed before a truly definitive conclusion can be made, however, and this kind of research is very difficult to conduct.

Scientists can either send spacecraft to these planets, or they can try to simulate the conditions on Earth. Both options require years of preparation, expensive equipment, and are subject to some of the toughest environments in the universe.

When scientists melted diamond under high temperatures and pressure and then resolidified, the solid diamond chunks floated on top of liquid diamond.

March 13, 2013, marks 20 years since the W. M. Keck Observatory began taking observations of the cosmos. Located in arguably one of the most extreme and beautiful places on the planet -- atop Mauna Kea, Hawai'i, 13,803 ft (4,207 m) above sea level -- the twin Keck domes have observed everything from asteroids, planets, exoplanets to dying stars, distant galaxies and nebulae. Seen in this photograph, the Keck I and Keck II telescopes dazzle the skies with their adaptive optics lasers -- a system that helps cancel out the turbulence of the Earth's atmosphere, bringing science some of the clearest views attainable by a ground-based observatory.

To celebrate the last two decades of incredible science, Discovery News has assembled some of the most impressive imagery to come from Keck.

Starting very close to home, the Keck II captured this infrared image of asteroid 2005 YU55 as it flew past Earth on Nov. 8, 2011.

Deeper into the solar system, the Keck NIRC2 near-infrared camera captured this beautiful observation of the oddball Uranus on July 11-12, 2004. The planet's north pole is at 4 o'clock.

This is a mosaic false-color image of thermal heat emission from Saturn and its rings on Feb. 4, 2004, captured by the Keck I telescope at 17.65 micron wavelengths.

A nice image of Saturn with Keck I telescope with the near infrared camera (NIRC) on Nov. 6, 1998. This is a composite of images taken in Z and J bands (1.05 and 1.3 microns), with the color scaling adjusted so it looks like Saturn is supposed to look to the naked eye.

This is Saturn's giant moon Titan -- a composite of three infrared bands captured by the Near Infrared Camera-2 on the 10-meter Keck II telescope. It was taken by astronomer Antonin Bouchez on June 7, 2011.

Another multicolored look at Titan -- a near-infrared color composite image taken with the Keck II adaptive optics system. Titan's surface appears red, while haze layers at progressively higher altitudes in the atmosphere appear green and blue.

This image of Neptune and its largest Tritan was captured by Caltech astronomer Mike Brown in September 2011. It shows the wind-whipped clouds, thought to exceed 1,200 miles per hour along the equator.

A color composite image of Jupiter in the near infrared and its moon Io. The callout at right shows a closeup of the two red spots through a filter which looks deep in the cloud layer to see thermal radiation.

HR 8799: Three exoplanets orbiting a young star 140 light years away are captured using Keck Observatory's near-infrared adaptive optics. This was the first direct observation by a ground-based observatory of worlds orbiting another star (2008).

Now to the extremes -- an image of Stephan's Quintet, a small compact group of galaxies.

The Egg Nebula: This Protoplanetary nebula is reflecting light from a dying star that is shedding its outer layers in the final stages of its life.

This is WR 104, a dying star. Known as a Wolf Rayet star, this massive stellar object will end its life in the most dramatic way -- possibly as a gamma-ray burst. The spiral is caused by gases blasting from the star as it orbits with another massive star.

Narrow-field image of the center of the Milky Way. The arrow marks the location of radio source Sge A*, a supermassive black hole at the center of our galaxy.

A high resolution mid-infrared picture taken of the center of our Milky Way reveals details about dust swirling into the black hole that dominates the region.

A false-color image of a spiral galaxy in the constellation Camelopardalis.

A scintillating square-shaped nebula nestled in the vast sea of stars. Combining infrared data from the Hale Telescope at Palomar Observatory and the Keck II telescope, researchers characterized the remarkably symmetrical “Red Square” nebula.

Galaxy cluster Abell 2218 is acting as a powerful lens, magnifying all galaxies lying behind the cluster's core. The lensed galaxies are all stretched along the shear direction, and some of them are multiply imaged.

The central starburst region of the dwarf galaxy IC 10. In this composite color image, near infrared images obtained with the Keck II telescope have been combined with visible-light images taken with NASA’s Hubble Space Telescope.

Keck I (right) and Keck II (left) domes at Mauna Kea.

Keck I and Keck II aim their adaptive optics lasers at the galactic center.