Mars Dust: What Perseverance Just Found at Jezero

Bolted to Perseverance's robotic arm, there are five little squares of spacesuit fabric. Each one about three quarters of an inch across. They've been sitting on Mars collecting dust for one thousand six hundred and forty-five Martian days.

A rover wearing swatches of spacesuit. Why?

Because nobody knows what Martian dust does to a spacesuit over a long stay. So NASA sent the fabric ahead of the humans. And on October twenty-sixth, they published what it caught.

Okay, and? Shredded? Scratched?

Almost untouched. After four and a half years, barely any visible wear.

Huh. So that's... good news? I was braced for something grim.

Half good. The grains on Mars turned out to be smooth. Scott VanBommel at Washington University in St. Louis led the study, and he put it like this: the particles have been blowing in the wind for potentially billions of years, so they're well rounded, like pebbles in a river.

Unlike the Moon, I'm guessing.

Lunar dust is jagged glass. On Apollo it scratched visors, chewed through outer suit layers, damaged seals. Some crews came back inside the lunar module and got symptoms like hay fever.

From dust they carried in on their knees.

Right. So Mars looked like the easier version. Then they measured how small the grains were.

How small are we talking? Give me a number.

Before this, the best measurements on Mars resolved particles down to about three micrometers. Guess what the instrument found this time.

I'll say... one micrometer? Under a tenth of what it was?

One hundred nanometers. Around five hundred times thinner than a human hair.

A hundred nanometers. That's smoke-particle territory.

That's exactly the comparison. On Earth, ultrafine particles from pollution and smoke are a serious health problem because they go deep into the lungs and cross into the bloodstream. The paper says these are small enough to reach the alveoli and threaten vital organs.

And the instrument that found them, what is it? A microscope?

An X-ray instrument called PIXL, on the arm. It does X-ray fluorescence, and VanBommel worked out a way to back out individual particle sizes from that data. Two bands: fine, under two and a half micrometers, and ultrafine, around a hundred nanometers.

Wait, but astronauts aren't breathing Mars air. It's in a suit, then a habitat. How does it get in?

On you. That's the Apollo problem again. And the chemistry is where Mars gets nastier than the Moon.

Nastier how?

Silica, iron compounds, and chlorine compounds including perchlorate, which can disrupt thyroid function. Plus reactive iron that can damage cells. The dust is also enriched in sulfur and phosphorus, and they saw signs of calcium sulfate.

Is that actually dangerous at Mars levels, or is this a "harmful at high doses" thing?

Honest answer: nobody knows. VanBommel keeps saying toxicity depends on dose and duration. No sample of real Martian airborne dust has ever been returned to Earth.

So the toxicity is inferred. Not measured.

Inferred from lunar dust toxicology and Mars simulants. NASA still wrote a rule this year. There's a new requirement in their human-system standard: keep dust under ten micrometers below a twenty-four-hour average of nought point one milligrams per cubic metre, for stays up to thirty days.

Where does that number even come from?

They took the lunar limit, nought point four, and applied a threefold uncertainty factor to land on nought point one, because they don't know enough.

That is the most honest piece of engineering I've heard all week.

And then there's the sticking. The two fabrics behaved completely differently. Vectran held the bigger grains, mostly on the underside of its weave. Teflon held less dust overall, but what it held was finer.

Why would the underside collect more? Gravity's the wrong way.

Electrostatics. Abigail Knight, a co-author, says the dust's electrical properties are making it preferentially stick to some surfaces. Charge, not gravity, is doing the sorting.

So picking your suit fabric is picking which size of dust you bring home with you.

And how you get out of the suit. NASA is studying suitports, which are docking stations where the suit stays outside and you climb in through the back, plus dual-chamber airlocks. VanBommel's line is that how much dust reaches a habitat depends largely on suit and airlock design, and that work is ongoing.

Ongoing meaning unsolved.

Unsolved. Nobody has ever tested a dust-tolerant suit on Mars. We have fabric swatches on a rover arm and a lot of simulant in labs in Texas.

And a crew staying how long? Months, with the launch windows.

Long enough that peak exposure after every single walk outside adds up. The panel that set the limit specifically flagged those spikes, right at suit ingress.

So before anyone opens a hatch, you'd want what, proof the airlock holds?

Proof the suit comes off without shedding into the cabin, filters that catch sub-micron particles, and some real toxicology on actual Martian dust. Mars Sample Return is meant to bring back at least one regolith sample in the twenty-thirties.

Which is roughly when people would be going anyway.

Yeah. Tight.

Four and a half years of a rover quietly wearing a scrap of spacesuit, and the headline is "it's fine, but it's really, really small."

That's about it. Smoother than the Moon, smaller than anyone measured, and we still can't say what a lungful of it does.

I'd want to know that before I signed.