'Super-Earths' may have life-protecting magnetic shields
Based on laboratory tests, scientists have suggested that exoplanets that are bigger than Earth but smaller than gas giants like Neptune could have oceans of liquid metal and life-protecting magnetic shields.
Laboratory tests showed that under the heat and pressure that exist inside super-Earths, magnesium oxide and other minerals commonly found in the rocky mantles of the terrestrial planets, transform into liquid metals.
The finding could help understand conditions on super-Earths, including whether they might be favourable for supporting life, Discovery News reported.
When the scientists zapped a piece of magnesium oxide with high-powered lasers to simulate the heat and pressure that would exist on planets roughly three to 10 times as massive as Earth, they discovered that the clear ceramic mineral first morphed into a solid with a new crystal structure, then completely transformed into a liquid metal.
In that state, the liquid mineral may be able to sustain a physics phenomenon called a "dynamo" action, which is responsible for generating magnetic fields.
"It is often thought that a planetary magnetic field protects life on a planet's surface from harmful space radiation, like cosmic rays. What we find is that magnetic fields may exist on more super-Earth planets than expected, resulting from the transformation of the planet's rocks to metals in the deep interior. This could create new environments for life in the universe," geophysicist Stewart McWilliams, with the Carnegie Institution and Howard University in Washington DC, wrote in an email to Discovery News.
Planetary scientist David Stevenson, with the California Institute of Technology in Pasadena, added, "The field certainly affects the way life evolves. I think it is an open question as to whether its absence inhibits the development of life."
"It is not easy for a terrestrial planet to generate magnetic field because the high thermal conductivity of the core material also allows heat to leak out by conduction, thus reducing the likelihood of convection. It is actually best to have a poor electrical conductor," he continued.
The discovery not only complicates models for understanding how planets form and evolve, but also blurs the distinction between a planet's core and its mantle.
The research has been published recently in Science.