10-07-2024

BepiColombo spacecraft reveals Mercury's magnetic secrets

Earth.com staff writer

On its journey in June 2023, the European Space Agency’s BepiColombo spacecraft had a brief encounter with planet Mercury’s magnetic field. It was a tantalizing preview of the mysteries BepiColombo aims to solve.

Even though Mercury’s magnetic field is one hundred times weaker than Earth’s, it creates a space bubble called a magnetosphere.

This magnetosphere acts as a buffer against the relentless particles projected by the Sun as the solar wind.

With Mercury’s proximity to the Sun, the interaction between the solar wind and the magnetosphere flares up more intensely than on Earth.

Insights into this intense space bubble and its particle properties promise to be the main attraction of BepiColombo’s mission.

Arrival at Mercury

The year 2026 is when BepiColombo is scheduled to reach Mercury. The journey, incorporating flybys of Earth, Venus, and Mercury, is vital for adjusting the speed and trajectory of the spacecraft.

However, the flybys have more to give than just a speed boost; they offer a sneak peek at the thrilling science that lies ahead and provide unique viewpoints of the planet that can’t be seen from orbit.

The scientific journey involves two science orbiters, the ESA-led Mercury Planetary Orbiter (MPO) and the JAXA-led Mercury Magnetospheric Orbiter (MMO or Mio). Their joint measurements will create a holistic picture of Mercury’s dynamic environment.

Mapping Mercury’s magnetosphere

The research was led by Lina Hadid, a former ESA Research Fellow, currently working at the Laboratoire de Physique des Plasmas at Paris Observatory.

She used the Mercury Plasma Particle Experiment suite to map Mercury’s magnetic landscape during one of the BepiColombo’s flybys.

Using data collected by the Mass Spectrum Analyser (MSA), Mercury Ion Analyser (MIA), and Mercury Electron Analyser (MEA), and combining these measurements with a computer model to determine the origin of detected ions based on their motion, various features encountered along the trajectory of the spacecraft were revealed. BepiColombo’s trajectory is shown as the yellow line in this graphic, with the various features encountered along the way labelled accordingly. Credit: ESA

“These flybys are fast; we crossed Mercury’s magnetosphere in about 30 minutes, moving from dusk to dawn at a closest approach of just 235 km above the planet’s surface, Lina explained.

“We sampled the type of particles, how hot they are, and how they move, enabling us to clearly plot the magnetic landscape during this brief period.”

Exploring Mercury’s magnetosphere

Marrying BepiColombo’s measurements with computer modelling, Lina and team were able to sketch out the features found in the magnetosphere.

They detected a low-latitude boundary layer marked by turbulent plasma at the magnetosphere’s edge. Surprisingly, they observed particles with a wider range of energies than seen before at Mercury.

“We also observed energetic hot ions near the equatorial plane and at low latitude trapped in the magnetosphere, and we think the only way to explain that is by a ring current, either a partial or complete ring,” added Lina.

A ring current is an electric current carried by charged particles trapped in the magnetosphere.

The spacecraft’s interactions with the surrounding space plasma were also noticed. As the spacecraft moved through the planet’s nightside shadow, cold plasma ions such as oxygen, sodium, and potassium became visible.

This gave them a glance at Mercury’s surface composition through the planet’s thin atmosphere, known as its exosphere.

Mercury’s exosphere and magnetosphere

Mercury’s exosphere, though very thin, gives us important insights into the planet’s surface and internal processes.

BepiColombo’s observations allow us to study particles released from Mercury’s surface into space, mainly made up of oxygen, sodium, and potassium.

This output from a simulation shows an expected case of Mercury’s magnetic environment under typical solar wind conditions. The left image shows a ‘side view’ where the Sun is out of frame to the left; the right image shows a ‘front view’ as if we are looking at Mercury from the direction of the Sun. The simulation is based on a model, it does not show real observations. The colors indicate the density of charged particles around Mercury, with the highest density shown in yellow and the lowest density in purple/black. Credit: ESA

Through the spacecraft’s sophisticated instrumentation, scientists are analyzing how these elements are affected by solar radiation and micrometeoroid impacts.

Understanding the dynamic interplay of these forces helps elucidate the way Mercury’s surface composition evolves over time.

By piecing together this information, researchers hope to uncover insights into the geological history and ongoing physical processes reshaping the smallest planet in our solar system.

Future discoveries

“In this rare dusk-to-dawn sweep through the large-scale structure of Mercury’s magnetosphere we’ve tasted the promise of future discoveries,” said JAXA’s BepiColombo project scientist, Go Murakami.

BepiColombo is set to contribute significantly to our understanding of planetary magnetospheres. As the scientists delve into the data from the recent flybys, the final two flybys scheduled for December 1, 2024 and January 8, 2025 are eagerly anticipated.

“We can’t wait to see how BepiColombo will impact our broader understanding of planetary magnetospheres,” concluded Geraint Jones, ESA BepiColombo project scientist.

The study is published in the journal Nature Communications Physics.

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