Mercury’s Hidden Heat: The Surprising Chemistry of a Frozen Planet

Mercury cooled early in its history, going volcanically quiet about one billion years after forming and leaving behind a frozen, rocky crust.

However, a new study in Planetary Research by the Max Planck Institute for Solar System Research reveals that Mercury’s interior was once far hotter and more dynamic than previously thought.a

Key Takeaways

1. Surprisingly Low Silica: Silicon dioxide (silica) makes up about 37% of Mercury’s surface material—up to 25% lower than prior estimates. By comparison, Earth rocks like basalt and granite contain up to 75% silica.
2. Signs of Extreme Melting: Because silica concentrations increase as molten rock cools and crystallizes, exceptionally low surface levels suggest Mercury's surface rocks came from deep mantle regions that underwent extensive melting at extreme temperatures.
3. The "Moon Test" Calibration: Because no spacecraft has collected samples from Mercury, researchers calibrated infrared data using lab-made 0.5 mm glass beads. They successfully verified this method against real Apollo lunar rocks before applying it to Earth-based telescope observations of Mercury.
4. Next Steps with BepiColombo: The joint ESA/JAXA BepiColombo mission will use its high-resolution MERTIS spectrometer to map Mercury's surface chemistry and test these findings up close.