The extreme pressure and temperature environments found in the cores of Earth-like planets were artificially developed in the laboratory using an ultrahigh-power laser at Lawrence Livermore National Laboratory.
The research was led by Richard Cross. They suggested that rocky planets larger than Earth must have strong magnetic fields that persist for more than billions of years.
This research could provide important pathway in the continued search for life on the ever-increasing number of Earth-like exoplanets that have been observed orbiting stars other in other solar system.
Because, planets like Earth (Exoplanets) are constantly being discovered by astronomers.
When a rocky planet forms, the material beneath its surface crust separates into a lighter silicate mantle that floats on a dense iron core.
The molten core gradually loses heat to the surrounding mantle Or in the case of Earth - the inner core freezes, releasing even more heat.
This movement of heat occurs through convection in Earth's molten outer core – activating a dynamo process that generates a strong magnetic field.
This region protects life on Earth from deadly radiation, and astronomers believe that such regions may be a prerequisite for biological life to emerge on other planets.
However, questions remain around the conditions that allow this convection to occur and remain constant over billions of years.
At the high pressure, high temperature environments of planetary interiors, convection of molten iron is adiabatic.
This means that there is a well defined temperature profile as it flows up and down.
At the same time the melting point of iron is known to depend on its pressure with respect to what is described by the melting state of iron.
Within a planet's core temperature and pressure change as a function of depth and iron, where temperature and pressure intersect the melting curve.
Within Earth, this intersection occurs closer to the center—resulting in a solid inner core and processes that can drive magnetic dynamos for billions of years.
If the intersection occurs further from the center, crystallization will occur in a "top-down" process - a bit like ice on a lake.
Here, solid "ice pieces" of iron form close to the edge of the core, leaving a molten center. In this snowstorm scenario, a magnetic dynamo is not expected to persist for long.
Heat and High Pressure
In their study, Krauss's team recreated these different conditions by heating the iron with an ultrahigh-power laser housed at LLNL's.
This generated a pressure of over 1000 GPa, which is three times that experienced by Earth's inner core. Using X-ray diffraction, the researchers could then analyze the melting curve of the iron.
The team found that the strongest magnetic fields emerge in planets with a radius about 1.5 times that of Earth and about five times the mass of Earth.
Such conditions produce a strong temperature gradient between the molten outer core and the mantle.
This in turn drives strong convection patterns in the molten iron, generating and maintaining magnetic fields for billions of years.
In contrast, Mars-sized planets are expected to have iron snowflakes – which have abundances of lighter elements in their cores, making it far more difficult to maintain magnetic fields.
About 1500 exoplanets identified so far, these results enable astronomers to better determine which of these may have the permanent magnetic field that could allow life to emerge.
(This article was originally published in Science Magzine)