Mars Attacks: How Much Dust From the Red Planet Is Safe to Breathe

A Rutgers mineralogist and planetary scientist helps NASA develop a limit for future astronauts

NASA has released a report recommending an initial health standard for the Martian dust that astronauts could inhale during future missions.

Rutgers planetary scientist Shaunna Morrison helped NASA develop an initial safety limit for the Martian dust future astronauts could breathe.

Although sending people to Mars is still years away, NASA needs to establish safety limits now. Spacecraft, spacesuits and crew habitats take years to design and test, and engineers need a measurable target for developing air filters, airlocks and suit-cleaning systems that will keep astronauts safe.

Martian dust presents an unusual challenge. It is extremely fine, can cling electrostatically to spacesuits and equipment, and may contain chemicals and minerals that could harm the lungs. Astronauts could carry it into their living quarters each time they return from working on the planet's surface. Establishing a standard now will also allow NASA to begin testing dust-control technologies well before a Mars mission launches.

Shaunna Morrison, a professor in the Department of Earth and Planetary Sciences in the Rutgers School of Arts and Sciences and a member of NASA's Mars Dust Limit Working Group, contributed her expertise in Martian mineralogy to the report. The group drew on rover and lander observations, laboratory simulations and lunar dust research to assess the risks of airborne Martian dust, which has never been brought to Earth for direct study.

Morrison, a mineralogist and planetary scientist, discusses why NASA needs a dust standard now, how the proposed limit was developed and what scientists still need to learn before astronauts travel to Mars.

What did the Mars Dust Limit Working Group recommend, and what would that limit mean in practical terms for astronauts?

The working group supported NASA's proposed initial limit of 0.1 milligram of fine Martian dust per cubic meter of air, averaged over 24 hours, for exposure scenarios lasting up to 30 days.

The limit is less about telling astronauts what to do minute by minute and more about giving engineers a measurable requirement for air handling, filtration, suit cleaning and habitat design.

In practical terms, this gives mission designers a target for how clean the air inside a Mars habitat needs to be, with particular consideration required for when astronauts come back from surface activities carrying dust on suits and equipment - likely the most common source of dust within the habitat.

A dust devil lifts fine particles from the Martian surface, highlighting the challenge of protecting future astronauts from airborne dust.

Why could Martian dust pose a health risk?

Very fine dust can get deep into the lungs, where it may cause irritation or inflammation, especially if exposure is repeated or prolonged.

Martian dust may also contain reactive iron-bearing phases, hazardous chemical compounds known as perchlorates, manganese, chromium, sulfates and other components that need to be considered, although our report concluded that controlling the total amount of dust is likely the most practical and significant near-term way to protect crews.

Because no samples of airborne Martian dust have been brought to Earth, how did the group determine a safe exposure level?

NASA has built the standard from the best available evidence - lunar dust toxicology, Martian regolith, which is the fragmented rock layer covering the surface of Mars, simulant studies and rover and lander measurements of Martian chemistry and mineralogy.

NASA experts started with the existing 30-day lunar dust exposure limit of 0.4 milligram per cubic meter of air and set a lower limit for Martian dust, adding an extra margin of safety to account for what scientists still do not know about it.

What is Martian dust made of, and which ingredients concern scientists most?

Martian dust is broadly basaltic, like many volcanic materials on Earth, meaning it contains minerals like plagioclase, pyroxene and olivine, along with iron oxides, sulfates, perchlorates, and a substantial amorphous, or poorly crystalline, component.

The ingredients that need the closest attention are fine respirable particles, such as iron-bearing and nanophase materials, such as perchlorate, manganese and chromium.

Current data suggests, however, that chromium and manganese are not likely to drive risk if the overall dust limit is maintained.

How could astronauts carry dust into their living spaces, and how would a Mars habitat monitor and remove it?

Astronauts would likely bring dust into the habitat after extravehicular activities, which are any task performed by an astronaut outside a spacecraft, when dust sticks to suits, boots, tools, airlock surfaces and equipment.

Humidity will also matter. In very dry air, fine particles can stay suspended longer and become more electrostatically "sticky," while higher humidity can change how particles clump, settle, and move through a filtration system.

Each habitat would need particulate monitoring, control of humidity and airflow, suit-cleaning procedures and filtration. HEPA filtration should be effective for Martian dust, but each vehicle or habitat filtration system would have to be designed and verified to remove dust quickly enough after an exposure spike.

What do scientists still need to learn about Martian dust before people travel to Mars?

We still need to know more about the actual airborne dust that astronauts would inhale - its particle size distribution, shape, mineralogy, surface reactivity, iron chemistry, perchlorate content and how much of each component becomes biologically available in the lungs.

One especially important knowledge gap is that the dust astronauts would breathe is not necessarily identical to Martian scooped soil, bulk regolith, or rock material we've studied in Martian meteorites. The finest airborne fraction may differ in size, chemistry and surface reactivity.

As a result, we still need to understand how easily it enters or clears from the lungs.

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