Mars's dense layer reveals the fate of rocky planets ⚡ экспресс
Crystallization of a magma ocean determines the early structure and long-term evolution of terrestrial planets. Seismic data indicate a silicate layer at the base of Mars' mantle, while no such layer is detected for Earth. Using a parameterized convection model, we investigated how partial melting in the growing mantle influences the composition of the magma ocean and can explain this difference. Mantle melts act as a buffer, limiting ocean differentiation, iron enrichment, and consequently the density contrast of an overturned layer. This buffer effect is more efficient for larger planets with vigorous mantle convection and for planets with initially lower iron content. Therefore, Mars' magma ocean became more iron-enriched and dense than Earth's, explaining the observed difference in mantle structures. The model also predicts a dichotomy in exoplanet interior structures: a population with small layered mantles and a population with large, predominantly homogeneous mantles.
If you don’t stir a layered cocktail, the heavy syrup sinks to the bottom. A young planet is much the same—a seething ocean of molten rock. As it cools, minerals crystallize: some, like iron, get heavy and sink, while others float. You’d think a dense layer would pile up at the core.
But from below, out of the solidifying depths, melts rise: light droplets, like oil in water, float up and churn the ocean. The bigger the planet and the hotter the 'stirring,' the harder it is for iron to settle.
The Martian ocean was shallower, the heat-driven motion weaker, and the iron quietly flowed to the bottom. This layer was recently detected through the echoes of marsquakes—it acts like a sponge, damping seismic waves.
The discovery explains the inner structure of many rocky exoplanets. In essence, we’ve read the recipe nature uses to cook up planetary interiors: some it stirs, others it lets separate into layers.
🎯 If Earth's interior had been as calm as Mars's, we would have formed a hidden dense layer too—and that would have completely changed the planet's look: continents would have moved differently, volcanoes would have erupted differently.