Could Chernobyl's Radiation-Eating Mould Shield Space Travellers from Cosmic Rays?

"Cladosporium sphaerospermum (radiotrophic fungus)"

Introduction — an unlikely contender for radiation protection

In the aftermath of the Chernobyl disaster scientists made an unsettling discovery: dark fungal growths coating reactor structures that not only survived extreme ionizing radiation but in laboratory settings showed growth responses linked to radiation exposure. These "melanized" or radiotrophic fungi have generated serious curiosity across radiobiology and space-exploration communities for one reason: melanin — the pigment that darkens their cells — appears to interact with ionizing radiation in ways that may reduce local dose and even support fungal metabolism.

What the evidence actually shows

Field and laboratory observations

Multiple teams have isolated melanin-rich fungi such as Cladosporium sphaerospermum, Wangiella and others from highly radioactive niches at Chernobyl. In controlled experiments, exposing certain melanized fungi to elevated ionizing radiation changed melanin chemistry and correlated with faster biomass accumulation — observations consistent with a radiation-influenced metabolism sometimes described as "radiosynthesis." Foundational experiments on melanin and fungi were reported by Dadachova et al. (2007, 2008).

Spaceflight experiments

In 2018–2019 researchers sent samples and cultivation experiments to the International Space Station (ISS) to measure growth under space radiation and to test attenuation. Results from these experiments (and follow-up analyses) reported a small but measurable reduction in detected ionizing radiation beneath a matured layer of Cladosporium sphaerospermum compared with controls; the attenuation for thin (millimetre-scale) layers was modest (a few percent), but constituted a useful proof of concept for biology-mediated attenuation. Subsequent peer-reviewed reports and preprints provide experimental detail and context.

How might melanin interact with ionizing radiation?

Melanin is a complex polymer with redox activity and broad electromagnetic absorption. In fungal cell walls it can:

absorb ionizing photons and secondary electrons, lowering the dose transmitted beyond the melanized layer;
participate in electron transfer chemistry that could convert radiation energy into chemical gradients; and
provide structural mass that contributes to stopping power against charged particles when present at sufficient thickness.

These properties do not imply miracles: melanin's effectiveness follows the same physics as any shielding material — you need material thickness and areal density to stop high-energy cosmic particles. Melanin can help, but mass and material composition remain determinative for protection against galactic cosmic rays (GCRs).

Engineering scenarios: what "fungal shielding" could actually mean

Translating laboratory attenuation into engineering practice requires realistic assessment of radiation types, required stopping power, mass budgets, and systems integration. Below are plausible architectures and the challenges each faces.

1. Thin, self-healing coatings for micro-shields

A thin living film of melanized fungi grown over critical electronics or secondary habitat surfaces could offer:

small reductions in local dose from gamma and secondary radiation;
self-healing after micrometeoroid abrasion if nutrients and environmental control are provided;
autonomous propagation that reduces replacement mass launched from Earth.

However, thin films are ineffective against high-energy GCR heavy ions; they are best positioned as supplemental protection where incremental dose reductions are valuable.

2. Biomanufactured composite regolith walls (ISRU + biology)

For planetary surfaces (e.g., Mars) a practical option is to use the fungus as a binder or melanin source mixed with local regolith to create composite shielding. This allows in-situ manufacturing:

carry a starter culture and nutrient feedstock from Earth;
grow fungal biomass and extract melanin or allow biomass to integrate with regolith;
construct thick walls (decimetres to metres) where mass comes from local soil instead of Earth launches.

Initial extrapolations indicate thin all-fungal layers are insufficient, but decimetre-scale composites with regolith could materially reduce surface dose on Mars when combined with other shielding strategies.

3. Melanin extraction and incorporation into synthetic shields

Another avenue is to culture fungi on orbit, extract melanin, and incorporate the pigment into hydrogen-rich polymer matrices. Melanin-enriched composites could offer a middle ground:

reduced launch mass versus metallic shields;
potential photon attenuation advantages per unit mass for certain energies;
engineering control over mechanical and thermal properties when combined with polymers and structural layers.

Key technical and biological constraints

Despite promise, several hard limits temper near-term expectations:

Mass vs. shielding tradeoff. Stopping GCR nuclei requires high areal density; biology helps only when paired with in-situ mass.
Radiation quality. Melanin attenuates photons and secondary electrons but is much less effective alone against high-energy heavy ions without substantial depth.
Biosafety and contamination risk. Carrying, growing, or dispersing terrestrial fungi in closed habitats or on other worlds raises planetary protection and human-health issues.
Life-support costs. Sustaining active growth requires water, carbon, and waste handling; these systems add mission complexity.
Engineering maturity. ISS and laboratory tests are promising but insufficient to validate full-scale shielding strategies.

Roadmap: how to assess feasibility rigorously

A staged research program can move radiotrophic fungi from an intriguing laboratory phenomenon to a practical engineering option:

Mechanistic studies: determine melanin's radiation absorption spectra and reaction pathways under vacuum and planetary-analog conditions.
Scale experiments: expose materials and composites to proton and heavy-ion beams that mimic GCR to measure attenuation vs. thickness.
ISRU process development: demonstrate melanin extraction and regolith-fungus composite fabrication at relevant scales.
Closed-habitat trials: test biosafety, off-gassing, allergenicity, and life-support integration in analogue habitats.
Flight demonstrations: extend ISS experiments to larger geometries and mixed-material composites before any planetary deployment.

Regulatory, ethical and planetary protection considerations

Introducing Earth microbes into extraterrestrial environments triggers international obligations under planetary protection frameworks. Deliberate release of terrestrial fungi on Mars or other bodies would require strong scientific justification, containment strategies, and community consensus. In closed habitats, human-health risk assessments and biosecurity procedures must precede any operational deployment.

Conclusion — promise tempered by physics

Melanized fungi discovered at Chernobyl and tested on the ISS present a scientifically exciting phenomenon: biological systems that interact with ionizing radiation in ways that can reduce local dose and, in limited contexts, convert radiation into chemical energy. As an engineering solution for crewed deep-space missions, fungal shielding is not a near-term replacement for mass-based shielding against galactic cosmic rays. However, used as a complementary approach — for coatings, ISRU composites, or melanin-infused materials — this biology could become a valuable tool in a broader radiation-protection strategy.