Super-Earths have longer shielding against cosmic radiation, new melting curve analysis suggests

Using one of the most powerful lasers on the planet, researchers have determined the melting temperature of iron at conditions like those in the cores of super-Earth exoplanets. The findings suggest that the presence of magnetospheres in super-Earth-sized planets is likely more prevalent and long-lasting than previously thought. The temperature at which iron melts under extreme pressures is important for terrestrial planets as it largely defines the size and nature of their liquid metal core, which can support a planetary magnetic field that protects the surface from harmful solar winds and charged particles. These protective magnetic fields are often considered necessary for habitability by life as we know it. Earth’s magnetic field is generated in the convecting liquid iron outer core surrounding a solid iron inner core. However, the extreme conditions in super-Earth exoplanets – those with masses several times bigger than Earth – aren’t well defined. As a result, whether such planets can host dynamo-generated magnetospheres isn’t well understood. Using the exceptionally high-energy lasers at the National Ignition Facility of Lawrence Livermore National Laboratory, Richard Kraus and colleagues determined the melting point of iron up to 1000 gigapascals (Gpa) – three times the pressure of Earth’s inner core and nearly four times greater pressure than any previous experiments. The findings show that a liquid metal core lasts the longest on planets four to six times larger in mass than the Earth, suggesting that super-Earths are likely to have a longer duration of magnetically shielded habitability than Earth. In a related Perspective, Youjun Zhang and Jung-Fu Lin discuss the study’s findings and limitations.