When scientists want to clarify whether or not an exoplanet is potentially habitable—probably the question they hear most every time they “hunt” for one of these distant extrasolar spheres—they look at questions like how close it is to its star or whether it has water. .
There is, however, another piece of information that can put you on the track: the ability of a planet to form a magnetosphere, a giant bubble of magnetism protect it from the solar wind. The Earth has one that protects us from most of the solar material that falls towards us. Without it, the world could lose the layers that protect us from ultraviolet radiation. Mars, today an arid and barren globe, lost its approximately 4.2 billion years ago.
That valuable armor, without which we would not have the atmosphere and life as we know it today, is linked in turn in the rocky planets to the movement of molten iron in the liquid core. Scientists refer to this displacement—driven by planetary convention and rotation—as a “dynamo” and it is key to magnetic fields.
Know the core of the super-earths
The challenge, when we talk about extrasolar terrestrial worlds, distant and of enormous size, is: How to know its core, the very bowels of the planet? And above all, how to do it for super-earths, gigantic worlds that can have ten terrestrial masses?
Scientists have managed to analyze the conditions of the cores of planets smaller than Earth, but if we talk about gigantic worlds, with much higher masses, the issue becomes quite complicated. There are simply few ways to reproduce the necessary pressures and temperatures in a laboratory. To achieve this, Rick Kraus of the Lawrence Livermore National Laboratory (LLNL), and his team have performed an amazing test that they now detail in Science.
During their experiment they used large lasers from the National Ignition Facility, at the Lawrence Livermore National Laboratory (California), and a very thin sheet of iron that they subjected to enormous pressure. During the process –detalla Popular Science— the outer level, beryllium, heated up to thousands of degrees in a fraction of a billionth of a second.
as you need the LLNL itself, determined the high-pressure melting curve and the structural properties of pure iron at nearly 10 million atmospheres, three times the pressure of the inner core of the Earth and four times more than what was achieved in any previous experiment. The goal: to emulate the conditions a hot iron sample would experience as it descended through the molten core of a planet, and ultimately to better understand extrasolar worlds.
His experiment is striking in method, of course; but also for the conclusions. Thanks to their work with lasers, they found that the larger a terrestrial exoplanet, the the longer its core takes to solidify. “We discovered that with a mass of four to six times that of the Earth they will have the longest dynamos, which provide important protection against cosmic radiation,” Kraus details in a statement released by the California body.
And –abounds Popular Science— in the case of the Earth, the core solidifies in a total of 6,000 million years, in the case of the large extrasolar planets with a similar composition could take up to 30% longer. Or seen in another way, the longer the molten nucleus lasts, the longer the conditions that scientists consider necessary for the generation of a magnetosphere and, consequently, the development of life as we know it, will probably exist.
The results help to better understand the structure and internal dynamics of exoplanets, worlds that astronomers began to study in the mid-1990s and that today make up a list of more than 4,500. “The great richness of iron within the rocky interiors of planets makes it necessary to understand the properties and response of iron in the extreme conditions deep within the cores of more massive planets,” reflects the LLNL expert: “The iron melting curve is essential for understand the internal structure, thermal evolution, as well as the potential of dynamo-generated magnetospheres”.
Cover Image | John Jett/LLNL