71 This only happens on Mars YouTube

The accumulation of dust donuts on the color calibration targets used by cameras on Perseverance means that Martian dust is behaving as expected. It also reveals a fundamental difference between dust on Mars and Earth. Our dust doesn't behave this way. On this episode of MarsGuy, two weeks ago, Perseverance completed a drive to get a better look at the rocks I reported on in the previous episode. Here's MarsGuy for scale. You can see that it required a sharp turn toward the end, which involves the rover's four-wheel steering doing a turn in place, leaving behind a nice donut, but not like the burned rubber kind from a muscle car on pavement. The initial location was just short of the drive target, so Perseverance had to reposition to get a better orientation on the slab of rock in front of it. But that position was still not quite right, so some additional fancy wheel work was required, which finally hit the spot. All these maneuvers left behind what may be the greatest density of wheel tracks anywhere on Mars, something for future rovers to aspire to. While parked here, Perseverance shot one of its routine images with the Mastcam-Z camera, a look back at its color calibration target. Shooting it at about 9 30 in the morning is somewhat unusual, and the low sun angle really highlights the increasingly thick dust deposits accumulating as neat little donuts around the color patches. But before I explain that story, there's the one presented on the Cal target in collaboration with the Planetary Society. It starts with Earth and Mars forming at the same time, with both possibly evolving DNA molecules and single-cell organisms, but then only one evolving multicellular plants and animals, one of which became capable of building rockets that could fly to Mars. The dust donut story starts with the clever use of little ring magnets underneath the color patches to help keep them clean. The idea to send magnets on spacecraft goes all the way back to the Lunar Surveyor program in the 1960s, which showed that the moon has magnetic particles in its regolith. In the 1970s, the two Viking landers carried magnets to the surface of Mars, including one to test if the dust there is magnetic. It is. Subsequent missions carried them as well, showing that little ring-shaped magnets could repel dust across a small circular area. Here's what that looks like using a ring magnet and a magnetic iron oxide mineral, appropriately named magnetite. It can occur at the few percent level in basaltic lava rocks, which are common on Mars and the moon. Magnets on Mars have shown that every particle of dust falling from the sky is magnetic, which is surprising given that Martian dust is not pure magnetite. Hematite gives it the reddish color, and there's also bits of silicates and salts in it, but none of these is magnetic. So somehow all these bits get stuck together along with magnetite to make Martian dust particles magnetic. How this happens is not clear, maybe electrostatics. What is clear is that typical dust that falls from the sky on Earth is not sufficiently magnetic to accumulate in neat little donuts. I collected this dust from the roof of my house in Phoenix, Arizona, where it hasn't rained in weeks. The circular magnet under the sheet of paper has no effect on the falling dust, so very un-Mars-like. And do try this at home. Someday, if your home is on Mars, your kids can make their own version of a classic Earth toy using magnetic Martian dust from your backyard.