Can Super-Earth interior dynamics set the table for habitability?
New research led-by Carnegie’s Yingwei Fei, provides a framework for understanding the interiors of super-Earths, rocky exoplanets between 1.5 & 2 times the size of our home planet, which is a pre-requisite to assess their potential for habitability. Planets of this size are among the most abundant in exoplanetary systems.
The paper is published in Nature Communications.
“Although, observations of an exoplanet’s atmospheric composition will be the first way to search for signatures of life beyond Earth, many aspects of a planet’s surface habitability are influenced-by what’s happening beneath the planet’s surface and that’s where Carnegie researcher’s longstanding expertise in the properties of rocky materials, under extreme temperatures & pressures comes in,” explained Earth & Planets Laboratory Director Richard Carlson.
On Earth, the interior dynamics & structure of the silicate mantle & metallic core drive plate tectonics and generate the geo-dynamo that powers our magnetic field and shields us from dangerous ionizing particles & cosmic rays.
Life as we know, it would be impossible without this protection. Similarly, the interior dynamics & structure of Super-Earths will shape the surface conditions of the planet.
With exciting discoveries of a diversity of rocky exoplanets in recent decades, are much-more-massive super-Earths capable of making conditions that are hospitable for life to arise & thrive?
Knowledge of what is occurring beneath a Super-Earth’s surface is important for determining whether or not a distant world is capable of hosting-life.
But the extreme conditions of Super-Earth mass planetary interiors challenge researchers ability to probe the material properties of the minerals likely to exist there.
That’s where lab-based mimicry comes-in.
For decades, Carnegie researchers are leaders at recreating the conditions of planetary interiors by-putting small samples of material under immense pressures & high temperatures. But sometimes, even these techniques reach their limitations.
“In order to build models that allow-us to know the interior dynamics & structure of Super-Earths, we’d to be able to take data from samples that approximate the conditions that might be found there, which could exceed 14 million times of the atmospheric pressure,” Fei explained. “However, we kept running-up against limitations, when it came to creating these conditions in the lab.”
A breakthrough occurred, when the team, including Carnegie’s Asmaa Boujibar & Peter Driscoll, along with Christopher Seagle, Joshua Townsend, Chad McCoy, Luke Shulenburger & Michael Furnish of Sandia National Laboratories, was granted access to the world’s most powerful, magnetically-driven pulsed power machine (Sandia’s Z Pulsed Power Facility) to directly shock a high-density sample of bridgmanite, a high-pressure magnesium silicate that’s believed to be pre-dominant in the mantles of rocky planets, so as to expose it to the extreme–conditions relevant to the interior of Super-Earths.
A series of hypervelocity shockwave experiments on representative Super-Earth mantle material provided density & melting temperature measurements which will be fundamental for interpreting the observed masses & radii of Super-Earths.
The researchers found, under pressures representative of Super-Earth interiors, bridgmanite features a very high melting point, which have important implications for interior dynamics.
They said, under certain thermal evolutionary scenarios, massive rocky planets may have a thermally driven geo-dynamo early in their evolution, then lose-it for billions of years when cooling slows-down.
A sustained geo-dynamo could eventually be re-started by the movement of lighter elements through inner core crystallization.
“The ability to make these measurements is crucial-to developing reliable models of the internal structure of Super-Earths up to 8 times our planet’s mass,” Fei added. “These results will make a pro-found impact on our ability to interpret observational data.”
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