DUSTER: Dusting the moon to discover its secrets

Did you ever wonder what hidden secrets are lying on the surface of the moon, waiting to be discovered by astronauts?

So did Bryce Bettens, Paulina Morales Ruiz, and Jan-Willem Burssens.
In the framework of their Science Communication and Outreach course, taught by prof. Katrien Kolenberg, these three students were challenged to create an immersive video for youngsters between 12 and 18 years old, as visual support to the latest issue of Belspo's magazine Science Connection. Instructed by Wim De Vos, external communication officer at Belspo, they came to interview Karolien Lefever about the DUSTER project.

The mystery of the moon

Q: Can you talk about what secrets you believe the moon holds, waiting to be uncovered by future exploratory missions?

Many people, including some scientists, think that the Moon is just a gray ball of rock in our sky and scientifically boring. However, the contrary is true.  Since the Moon lacks an Earth-like atmosphere, its surface stays virtually unchanged for years. It’s like a geological time capsule… Even the booth steps of the Apollo astronauts are still visible on the surface. One could say “What happens on the Moon, stays on the Moon… forever”.

During the early Solar System, asteroids and comets have been bombarding planets and their moons. Most craters formed from such impacts on Earth are no longer visible due to erosion by wind and water. But the Moon has preserved most of its craters in roughly the same condition for millions and millions of years. This can teach us a lot about the history of our solar system, and maybe even about how water and life could emerge on Earth.

There are still so many things to learn about the Moon. For instance, since we are seeing from the Earth always approximately the same side of the Moon, it is only recently that we have started to discover what is happening on the back side of the Moon. Half of the moon is yet to explore!

Q: Why should we care about the moon? What role will the moon play in the future of space exploration?

Future human explorers, to Mars or to the Moon, will have many challenges to face. They will need to deal with space radiation, with high UV radiation from the Sun, they will need to find ways to create oxygen to breathe, they will need to find water to be able to drink.

In the preparation of exploratory missions to Mars, the moon is a great step-in-between. It takes about 3 days for a spacecraft to travel to the Moon, while a trip to Mars lasts about 7 months, at least. Our Moon’s proximity makes it a great testbed of technologies required for deep space exploration.

For example, in the last two decades, water ice was discovered on the Moon’s poles. Water is one of the key ingredients to sustain life on another solar system object. We still need to learn how to extract this water and turn it into drinkable water for future human explorers.

Another example: scientists study our Moon to understand how space radiation and micrometeorite bombardment can affect astronauts living in deep space for long periods, including on Mars missions.

NASA is currently preparing the international Gateway station, in orbit around the moon. It will specifically study the long-term impacts of deep space radiation on astronauts. In the long run, the Moon’s low gravity barrier could also make it an efficient rocket platform to travel across the Solar System.

Q: Can you explain what the value is of investigating lunar dust?

Dust is one of the major challenges that future astronauts on the moon will have to face. It impacts not only the health of astronauts, since it can deeply penetrate in the breathing airways and lungs of astronauts, but it also impacts technology on the surface. Lunar dust is highly ‘static’ and clings to every surface. The spacesuits of Apollo astronauts were covered with the dust, it obstructed their sight, but it also covers solar panels; it can block some mechanisms; …

However, there are still so many things we don’t know about the lunar dust particles. Their size distribution, their electrical charging properties, how they interact with the ultraviolet light from the Sun, with the solar radiation and space radiation, how they get lifted and how they are transported, how well they stick together.

In order to be able to correctly deal with it (mitigate their adverse effects), we need to characterise them properly.

The challenge

Q: Why is dust on the moon such a big threat?

Something dust on the Earth and Moon have in common is that dust particles can be a real nuisance, and we generally prefer to get rid of it.

On the Earth, that’s rather easy, we use a vacuum cleaner or a dust cloth, or we wipe it off with our hands.

On the Moon, that’s not so easy. The dust is electrically charged and clings to every surface. Wiping it off with our hands is not possible. It just sticks to it. It is even dangerous to do so.

On Earth, pebbles are rounded by the natural elements over time, making them easy to deal with. Lunar soils, however, are not exposed to erosion. Lunar dust is created by micrometeorite impacts (a bit more than 100 kg/year), breaking the top layer of the lunar surface in ever smaller pieces, almost like powder, but leaving them very sharp (like glass) and angular, with fresh fractures surfaces due to the absence of rain or wind. Since they are so small (they can be less than 20 microns in size, as thin as a hair), they can be very damaging in ways we don’t see on Earth. As mentioned, when astronauts inhale air filled with such sharp particles, you can imagine the damage it can cause. When it obstructs instruments, sometimes needed for the safety of the humans explorers.

On Earth, most of these micrometeorites never reach the ground, they already burn up in the atmosphere. We can see them as shooting stars.

Q: Can you explain, in a simple way, what is the electrostatic force of dust on the moon?

Unlike on Earth, Moon dust isn’t packed down. Any activity on the surface can kick up buckets-full of it, but even without astronauts walking around on its surface or a lunar module putting feet on its soil, dust particles and clouds have been seen floating several centimetres to metres above the surface. Despite the fact that there is no wind or water flowing on the surface to lift them up! Tiny particles can even be transported across vast distances on the Moon. Scientists attribute the dust mobilisation to electrostatic forces.

Although the physical and dynamical processes behind dust lifting and transport are not yet entirely understood, we know that Moon dust may look and behave differently depending on its location on the surface compared to the Sun (the solar zenith angle).

For example, the sun-facing side (the dayside) is constantly exposed to solar radiation. Irradiation of material on the surface in the UV and X-ray range results in photoemission of electrons (i.e. the release of negatively charged particles). This causes the dust on the dayside to have a slight positive electrical charge, with a potential of about +10V, which means that it clings to everything – like static effects here on Earth.

On the nightside, charged particle interactions tend to induce a negative potential, estimated to lie normally between -100 V and -200 V.

Near the terminator, the region between the shadowed and the sunlit sides, strong electric fields are present because of the fast transition from positive to negative potentials. This electric field could be the cause of electrostatic levitation and horizontal transport of lunar dust grains, leading to the net deposition of dust from the dark into the sunlit hemisphere.

The DUSTER Project

Q: Can you introduce the project? How can it contribute to solving the dust problem?

DUSTER is a project led by the Royal Belgian Institute for Space Aeronomy, in collaboration with Instituto de Astrofisica de Andalucia, ONERA (the French Aerospace Lab) and Thales Alenia Space in Spain, and funded by the European Commission through its Horizon Europe programme.

DUSTER (which is short for ‘Dust Study, Transport, and Electrostatic Removal for Exploration Missions’) aims to study the physical properties of lunar dust, in particular the electrostatic charging and adhesion of dust grains in the lunar surface, which is crucial to understanding the dust transport. In first instance, we do that using lunar dust simulants in the laboratories at ONERA. Using a dedicated setup in which we simulate a lunar environment, we try to measure the electric field at the surface of the dust layer, to attract and move charged grains by applying an electric field, to measure the resulting current and the electric charge carried by the mobilized grains.

Based on these results, we develop an instrument that can perform these measurements in-situ, at the lunar surface, in an uncontrolled environment. We hope to be able to install it on a future lunar lander to assess dust pollution risks and to find ways of efficiently mitigating its dangers.

Unlocking Lunar Secrets

Q: What does increasing our knowledge on lunar dust mean for the future?

The Apollo astronauts did not stay on the Moon’s surface long enough for serious and irreversible health issues to result from their exposure to lunar dust. However, it became apparent that the effects of the dust on the human body, and on safety-critical equipment had been underestimated.

If we have a better understanding of the lunar dust, we can find ways to overcome issues related to the negative effects of it, e.g. on a lunar landing site. We could effectively remove dust from the astronauts spacesuits, remove it from the space instruments.

Q: How can dust unlock new opportunities for scientific discovery and space exploration?

By developing the technology required to electrostatically move the dust grains in a controlled way, it constitutes a first step toward a sensitive surface cleaning device, but also to dust sample collectors, as you can either attract or repel it. It would greatly facilitate the lives of future space explorers, both on the Moon and on Mars.