Extraterrestrial life can survive better on super-Earths • The Register
Life on super-Earths may have more time to grow and evolve, thanks to their long-lasting magnetic fields protecting them from harmful cosmic rays, according to new research published in Science.
Space is a dangerous environment. Streams of charged particles moving at the speed of light, ejected from distant stars and galaxies, bombard the planets. The intense radiation can strip atmospheres and cause oceans to dry up on planetary surfaces over time, leaving them arid and unable to support habitable life. Cosmic rays, however, are deflected from the Earth, as it is shielded by its magnetic field.
Now, a team of researchers led by the Lawrence Livermore National Laboratory (LLNL) believe super-Earths — planets more massive than Earth but less than Neptune — might also have magnetic fields. It is actually estimated that their defensive bubbles remain intact longer than those around Earth, which means that life on their surface will have more time to develop and survive.
“While there are many requirements for a habitable planet, such as a surface temperature that allows liquid water, having a magnetosphere that can shield against solar radiation for long periods of time could provide long durations for life evolves,” Richard Kraus, lead author of the paper and a physicist at LLNL, said The register.
The key to long-lasting magnetic fields is having a liquid metal core that cools more slowly. The Earth’s magnetic field is generated by a layer of molten iron swirling around a solid iron core. The electrons in the liquid move to create electric currents which feed a magnetic field.
The temperature of molten iron buried under 2,890 kilometers or 1,800 miles of the Earth’s surface, however, is freezing. It will eventually cool until it solidifies completely. At this point, its internal dynamo will stop spinning and it can no longer withstand a magnetic field. The Earth’s magnetic field will disappear in about 6.2 billion years.
“As the iron solidifies, it releases energy along with lighter elements into the liquid iron, which provides the energy needed to power the dynamo over long periods of time. At some point, the temperature of the liquid core will will cool to melting temperature, which means it will start to solidify,” Kraus explained. The iron inside Super-Earth is compressed to much higher pressures than Earth, and its melting temperature is also higher.
In other words, the cores of Super-Earths must be cooled to much lower temperatures before solidifying. Their larger cores also mean they lose heat at a slower rate than Earth.
“We find that super-Earth nuclei will take up to 30% longer to solidify than the Earth’s core…Due to the competing effects of energy stored with respect to the surface, the nuclei planets smaller than Earth will solidify rapidly, with the maximum time scale for solidification occurring in [Super Earths four to six times the mass of Earth]“, concludes the newspaper.
Kraus and his colleagues were able to simulate the internal conditions of a Super-Earth by studying the melting behavior of iron at pressures of 1,000 gigapascals, nearly three times the pressure of the Earth’s core. The team zapped a tiny milligram fragment of iron with a series of lasers to compress it to increasingly higher pressures.
Experiments have shown that at 1,000 gigapascals, the melting temperature of iron is around 11,000 degrees Celsius. For comparison, the Earth’s internal pressure is around 330 gigapascals and its core has a melting temperature of around 6,000 degrees Celsius.
“This is the first experiment to measure the melting curve of iron at pressures greater than 290 gigapascals, meaning it is the first to constrain the melting temperature of iron under Super Earth core conditions” , said Klaus. El Reg.
“Astronomers will use these results, along with their observational data, to paint a better picture of what is happening in and on the surface of exoplanets.” ®