Mars dirt looks deceptively ordinary, yet samples contain around 0.5% perchlorate salts that can disrupt the human thyroid — meaning the red dust astronauts track inside their habitat could be chemica
Martian soil contains perchlorate salts that pose a significant health risk to astronauts by interfering with thyroid function if tracked into habitats. NASA is currently developing engineering controls to manage this chemical hazard during future crewed missions.
Why it matters
Understanding the chemical toxicity of Martian dust is essential for the safety and long-term viability of human space exploration.
Phoenix measured 0.4 to 0.6 per cent perchlorate in Martian soil. NASA's 2026 dust limit shows why the thyroid hazard is real but manageable through habitat engineering.
By Lachlan Brown · Edited by Lachlan Brown
Mars does not need an exotic poison cloud to create a chemical problem for astronauts. The material underfoot is enough. In 2008, NASA’s Phoenix lander mixed scoops of northern Martian soil with water inside its Wet Chemistry Laboratory and detected perchlorate at 0.4 to 0.6 per cent by mass.
At 0.5 per cent, a kilogram of soil contains roughly five grams of perchlorate. These salts can interfere with the thyroid’s uptake of iodide. Fine soil carried back on spacesuits could therefore become more than a cleaning nuisance if it enters a pressurised habitat day after day.
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