Planets generally get cooler with age, but Saturn is hotter than it should be if it is as old as astrophysicists believe it is.
The mysterious excess heat has caused a two-billion-year discrepancy for computer models that work to estimate the planet's age, Sandia National Laboratory reported.
"Models that correctly predict Jupiter to be 4.5 billion years old find Saturn to be only 2.5 billion years old," said Thomas Mattsson, manager of Sandia's high-energy-density physics theory group.
New experiments at Sandia's Z Machine could help solve this mystery. The machine allowed the scientists to verify that the insulator molecular hydrogen becomes metallic if subjected to enough pressure. When this phenomenon occurs, a lattice of hydrogen molecules beaks up into individual hydrogen atoms, releasing free-floating electrons that can carry a current. The findings back up a theory that was first proposed by physicists Eugene Wigner and Hilliard Huntington in 1935.
"That long-ago prediction would explain Saturn's temperature because when hydrogen metallizes and mixes with helium in a dense liquid, it can release helium rain," said Sandia researcher Mike Desjarlais.
"Essentially, helium rain would keep Saturn warmer than calculations of planetary age alone would predict," added Sandia researcher Marcus Knudson.
The Z machine is the world's most powerful pulsed-power machine, which has the ability to send sub-microsecond pulses of electricity to a target. The magnetic field surrounding the pulse squeezes present deuterium (a heavier variant of hydrogen) at a low temperature.
"We started at 20 degrees Kelvin, where hydrogen is a liquid, and sent a few hundred kilobar shock - a tiny flyer plate pushed by Z's magnetic field into the hydrogen - to warm the liquid," Knudson said. "Then we used Z's magnetic field to further compress the hydrogen shocklessly, which kept it right above the liquid-solid line at about 1,000 degrees K." (One thousand degrees K is approximately 1,800 degrees Fahrenheit.)
When the liquid was compressed to over 12 times its starting density, it was observed to become atomic rather than molecular. The transition, at three megabars of pressure, provided scientists with a solid figure to use in their calculations to create more accurate computer models.
"The Sandia work shows that dense hydrogen can be metallic, which in turn changes the coexistence of hydrogen and helium in the planet," Mattsson said. "The mechanism of helium rain that has been proposed is therefore very plausible, given our results, but the scientific discussion will continue over the next few years in establishing a new consensus."
The findings were published in a recent edition of the journal Science.
