Mars is one of the closest planets to Earth and has been studied extensively with multiple scientific instruments aboard the various unmanned space probes that have explored it. We continue to do so in order to dig out information that has not been known till now.
Even after such endeavours, some questions about Mars remains unanswered, the questions which could potentially shed light on our own distant past and future, given the fact that Earth, Mars and all our neighbouring planets were born out of the same celestial matter. We have dug out the answers to one big question that some visible features of Mars prove that in the past, it had oceans and an active magnetic field.
Since the researchers now know that Mars had an active magnetic field around 4.3 to 4.2 billion years ago, Professor Kei Hirose from the University of Tokyo‘s Department of Earth and Planetary Science had one particular question on his mind as to why Mars had the magnetic field and why it lasted so briefly. A team of researchers led by PhD student Shunpei Yokoo explored a new method in the Hirose lab to test something and find the answer to this question.
Professor Kei Hirose said that the Earth’s magnetic field is powered by the huge convection currents of molten metals it has in its core. The magnetic fields of other planets are also believed to work in the very same way. Although the internal composition of Mars is not yet known, evidence collected from numerous meteorites suggests that it has molten iron enriched with sulphur. Also, the seismic readings received from NASA’s InSight probe highlights that the core of Mars is larger and is less dense than was previously believed. These things suggest that there is a presence of additional lighter elements such as hydrogen. Keeping this detail in mind, we prepared iron alloys that we expect to constitute the core of Mars and subjected them to experiments, professor Hirose added.
In the experiment, Yokoo made a sample material containing iron, sulphur and hydrogen, which is expected to be once the components of the core of Mars. The team placed this sample between two diamonds and compressed it, all the while heating it with an infrared laser. This was done to simulate the estimated temperature and pressure at the core. Sample observations with X-ray and electron beams allowed the team to figure out what was going on during the melting process under pressure. The team mapped how the composition of the sample changed during the process.
The sample material, which was homogeneous Fe-S-H at the start, separated out into two specific liquids, with a level of complexity that is generally not seen under these kinds of pressures, Hirose explained. Out of the two, one of the liquids was rich in sulphur, while the other was rich in hydrogen. This makes up as the key to explaining the birth and eventually the death of the Martian magnetic field.
Hirose further detailed that since the liquid iron that was rich in hydrogen and poor in sulphur was less dense, it would have risen above the denser sulphur-rich liquid iron, which was poor in hydrogen. This movement may have caused the convection currents. These convection currents, in turn, may have driven the magnetic field that was capable of trapping the hydrogen in the atmosphere around Mars. This phenomenon in turn would have allowed the water to exist in the liquid form. However, once the two liquids had separated completely, there would have been no more convection currents to drive the magnetic field. As a result, the hydrogen present in the atmosphere would have been blown out to space by the solar winds, which may have led to the breakdown of water vapour and eventually led to the evaporation of the Martian oceans. He noted that all this would have taken place about 4 billion years ago.
Hirose said that he and his team were hopeful that further seismic study of Mars will verify that the Martian core is indeed in distinct layers as they have predicted. If the prediction is proved right, it would help the team of researchers to complete the story of how the rocky planets, including Earth, formed, and could even explain their composition, Hirose added. He also said that the Earth too could lose its magnetic field one day, but that won’t happen for at least another billion years.
Journal Reference: Shunpei Yokoo, Kei Hirose, Shoh Tagawa, Guillaume Morard, Yasuo Ohishi. Stratification in planetary cores by liquid immiscibility in Fe-S-H. Nature Communications, 2022; 13 (1) DOI: 10.1038/s41467-022-28274-z
