Mercury is a mystery.
It’s the smallest planet in our solar system, the closest to the Sun, and one of the most extreme. Its surface is scorched, its core is massive, and its rocks are unlike anything we find on Earth.
For scientists like Anne Pommier, an experimental geophysicist at Carnegie Science, Mercury is full of puzzles waiting to be solved.
Despite its importance, we’ve only sent two missions to Mercury: Mariner 10 in the 1970s and NASA’s MESSENGER, which orbited the planet from 2011 to 2015.
These missions revealed Mercury’s strange magnetic field, metal-rich makeup, and volcanic plains—but also left many questions.
Why is its core so large? How did it form? And why does it still have a magnetic field?
Mercury’s core makes up 60% of its volume—far more than Earth’s, which is about 15%. Some scientists think Mercury was built from metal-rich materials; others believe violent early collisions stripped away much of its rocky outer layer.
Pommier says that to find the truth, we need more field data, lab experiments, and computer models.
That’s why the upcoming BepiColombo mission, led by Europe and Japan, is so exciting. Scheduled to start orbiting Mercury in 2025, it will collect new information about the planet’s chemistry, magnetic field, and electrical properties. But to make sense of that data, scientists need to understand how Mercury’s unusual rocks behave under extreme conditions.
Pommier’s lab is helping fill in the gaps. Her team creates Mercury-like materials in the lab—rocks that form in low-oxygen, sulfur-rich environments, which are very different from Earth’s. These lab-made samples are then studied using high-tech tools to learn how they melt, flow, and change.
One big discovery is how lava behaves on Mercury. Earth’s lava is thick and sticky because of strong bonds between silicon and oxygen. On Mercury, those bonds are replaced by shorter silicon-sulfur links, making the lava much runnier. This may explain why Mercury’s volcanic plains are so smooth.
Another big puzzle is Mercury’s magnetic field. It’s weak, but still active—a surprise for a small planet that should have cooled and “died” long ago. Pommier and her colleague Christopher Davies ran thousands of simulations and found that Mercury likely has a growing solid inner core and a very thin, slowly shrinking layer of molten metal that still generates a magnetic field.
Beyond helping us understand Mercury, this kind of research has real-world benefits. The same tools used to study Mercury—like high-pressure machines and thermal models—are also used in developing new materials, improving electronics, and solving energy problems.
For Pommier and her team, Mercury is more than just a weird planet—it’s a key to understanding how rocky planets form and evolve. In fact, Mercury is so unusual that scientists call it “an exoplanet in our own backyard.” As new data arrives from BepiColombo, the insights from lab experiments will help scientists make sense of it all, opening a new chapter in our exploration of the solar system.
Source: Carnegie Institution for Science.
