Lumieux: A small European probe to detect meteor impacts on the far side of the Moon

What do the James Webb Space Telescope and the Moon have in common? That both are excellent near-Earth space meteor detectors, the JWST with its mirror – inadvertently, unfortunately – and the Moon with its surface. This may seem strange at first, because on Earth we can see meteors or shooting stars when they burn up in the atmosphere – as well as detect them by radio – but the Moon lacks a layer of air around it. The answer is, precisely for this reason, that we are able to detect meteors because when they hit the surface directly at a very high speed, they generate a small fireball that can be seen by ground-based telescopes. The theory is simple, but the reality is that detecting these collisions with the Moon is no easy task. In fact, the first confirmed impact caused by a meteorite occurred in 1999 while Leonid was showering. We had to wait until 2005 to make a detection by more than one observer. Detecting these effects from Earth has another problem, which is that it cannot be done in the bright regions of the lunar disk or when our satellite is close to the Sun in the sky. And of course, we can’t observe the far side of the moon either.

LUMIO observes the hidden face of the Moon (ESA).

Because of these limitations, in 2017 the LUMIO proposal was born (Lunar Meteorite Impact Monitor), a probe capable of continuously observing the far side of the Moon from the L2 Lagrange point in the Earth-Moon system. LUMIO is a small satellite weighing about 29 kg based on a 12U cube design equipped with a powerful camera, LUMIO-Cam, capable of seeing the afterglow of meteor strikes on the lunar surface. After passing Phase 0 of its design in 2017, the initiative has completed Phase A of development in 2021. LUMIO is a project supported mainly by Italy, Norway and the Netherlands. LUMIO is an excellent complement for terrestrial observers dedicated to discovering the impacts of meteorites because when the moon is full for us, LUMIO will be a new moon, and vice versa, in addition to the advantage derived from being able to observe the hemisphere of our satellite that we are not able to see from our planet. Another advantage is that the unlit part of the Moon that LUMIO sees will be completely dark, without the ash-like glow of light from Earth illuminating the dark areas on the near side. Of course, feedback will only be possible when the hidden face is illuminated by half or less, otherwise the camera sensors will be oversaturated.

LUMIO will complement observations of meteor strikes from Earth (Topputo et al.).

The goal of LUMIO is to measure the density of particles in lunar space. As the James Webb telescope itself witnessed in its mirror, meteorites are a danger to our fleet of satellites beyond low orbit, but we don’t know how many large interplanetary dust particles are in our neighbourhood. Estimates vary between 1,000 and 4,000 impacts per year against the Moon by meteorites greater than 1 kg. For meteorites larger than 30 grams, studies indicate 23,000 strikes annually against the Moon. On the other hand, some researchers have suggested that the hidden side could experience less shocks than the visible side – only 0.1% less – due to the influence of Earth’s gravity and that the tropics would receive up to 20% more shocks than the polar region. Of them, due to the orbital plane of most interplanetary dust particles. Likewise, it is believed that the moon’s left hemisphere, located “forward” in the direction of progression in its orbit, will experience 40-80% more shocks than the other hemisphere. But no one corroborated these numbers, and this is where LUMIO must play an essential role. Of course, not only will these numbers help us better protect our satellites or lunar bases, but they will also test models of our solar system.

A view from LUMIO (Topputo et al.).
Lumio Cam (Tobuto et al.).

With a 5.1-cm aperture, the LUMIO-Cam will capture an image of the moon at 15 frames per second in visible and near infrared. In this way it will be possible to distinguish flashes in detectors caused by cosmic rays or other particles. LUMIO will need to work for a year and a half at point L2, by which time it is expected to detect thousands of meteor strikes (it’s estimated that it will be able to see up to 6,000 meteor showers during heavy showers like the Geminids). Japanese EQUALEUS 6U cubes (Spacecraft EQUilibriUm Lunar Earth Point 6U), launched in November 2022 on NASA’s Artemis I mission. Among its goals is also the detection of this type of collision, but it is not a mission dedicated to this mission like LUMIO. Due to its small mass, LUMIO can be launched as a secondary payload on any lunar or planetary mission. Undoubtedly, a very interesting initiative that, if approved, could increase the safety of future space telescopes and manned missions to the Moon.

LUMIO trajectory (ESA).



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