Laying some groundwork for BepiColombo

Category: Cover Story

Subscribe to our newsletter.

In 2022, the Planetary Science Institute hosted a virtual workshop titled “Mercury’s Surface Response to the Interplanetary Environment: Identifying Needed Studies in Laboratory Astrophysics.”

From the workshop, participants generated four review papers to guide future laboratory studies in preparation for BepiColombo, an international mission undertaken by the European Space Agency and the Japan Aerospace Exploration Agency. It is comprised of two spacecraft launched together to Mercury. There, they will orbit and study the complex system that makes up the innermost planet of our Solar System. BepiColombo is only the third mission to explore Mercury. The spacecraft are expected to arrive and enter orbit at Mercury in November 2026.

Two review papers have been published in the Planetary Science Journal.

Paper one: Turning the heat up on Mercury

As the closest planet to our Sun, Mercury is highly influenced by the temperature cycles induced by the Sun’s energy, what scientists call solar flux. This is especially true because Mercury has no substantial atmosphere to temper the input of light that heats the surface, but rather an extremely thin exosphere comprised of a smattering of atoms.

In this context, the first of four papers to come out of the workshop explores the state-of-the-art in modeling how temperature affects the movement and loss of volatiles, which are substances that vaporize at low temperatures. The paper also outlines laboratory experiments needed to validate the models that describe and quantify how the solar flux works to contribute to forming the exosphere, the powdery soil and alter the minerals on the surface.

“Solar flux is not limited to the extreme day/night variations on Mercury, but also variations due to both large scale topography and even the shadows cast by grains on other grains,” said PSI Senior Scientist Deborah Domingue, who served as paper co-author and workshop co-convener.

“Digging into this relationship will help us to understand what can be learned from the exosphere on its surface and below and vice versa,” said lead author François Leblanc of the Laboratory for Atmospheres, Observations, and Space at Sorbonne University in France.

A roughly quarter millimeter-wide spherule from Apollo 11 lunar sample depicting the remnants of a micrometeoroid, or dust, impact. These impacts melt and vaporize portions of the lunar soil grains, which contribute not only to the alteration of the soil but to constituents in the lunar exosphere. These same processes are also occurring on the surface of Mercury. Credit: NASA.

Paper two: Mercury’s dance with dust

The second paper focuses on the role of micrometeoroids, or dust, on Mercury. Dust might be tiny, but it can still have an impact on planetary bodies that lack a protective atmosphere, like Mercury.

Scientists want to understand how dust weathers the planet’s rocky surface. This involves understanding how the magnetic field affects dust’s journey to the surface and how the impact of these tiny particles melt, vaporize and modify the material that makes up the surface.  

“In this manuscript, we discuss the sources of dust – such as the zodiacal cloud, cometary trails and interstellar dust – and how our models reflect what has been observed by the MESSENGER mission, which orbited Mercury between 2011 and 2015. We again also outline the laboratory investigations needed to improve our models in anticipation of BepiColombo measurement operations,” said Domingue, who was also a co-author on this paper.

“Mercury is exposed to a harsh interplanetary environment, with higher solar wind flux and micrometeoroid flux than other, well-studied Solar System bodies like the Moon. Simulating these processes in the laboratory will be critical to the interpretation of data to be returned by BepiColombo,” said Michelle Thompson of Purdue University. Thompson led the paper along with Harald Krüger of the Max Planck Institute for Solar System Research.

Papers three and four will be discussed in future cover stories.