Seeing Mars in a Particle of Dust

NASA’s Phoenix lander is seen here collecting a sample of martian soil for analysis by the lander’s Thermal and Evolved-Gas Analyzer (TEGA).
Credit: NASA/JPL-Caltech/University of Arizona/Max Planck Institute

NASA’s Phoenix Mars Lander has taken the first-ever image of a single particle of Mars’ ubiquitous dust, using its atomic force microscope.

The particle — shown at higher magnification than anything ever seen from another world — is a rounded particle about one micrometer, or one millionth of a meter, across. It is a speck of the dust that cloaks Mars. Such dust particles color the martian sky pink, feed storms that regularly envelop the planet and produce Mars’ distinctive red soil.

"This is the first picture of a clay-sized particle on Mars, and the size agrees with predictions from the colors seen in sunsets on the Red Planet," said Phoenix co-investigator Urs Staufer of the University of Neuchatel, Switzerland, who leads a Swiss consortium that made the microscope.

"Taking this image required the highest resolution microscope operated off Earth and a specially designed substrate to hold the martian dust," said Tom Pike, Phoenix science team member from Imperial College London. "We always knew it was going to be technically very challenging to image particles this small."

It took a very long time, roughly a dozen years, to develop the device that is operating in a polar region on a planet now about 350 million kilometers or 220 million miles away.

This image taken by the Optical Microscope on Phoenix shows soil sprinkled from the lander’s scoop onto a silicone substrate. The substrate was then rotated in front of the microscope. This is the highest resolution image yet seen of martian soil. The image is dominated by fine particles close to the resolution of the microscope. These particles have formed clumps, which may be a smaller scale version of what has been observed by Phoenix during digging of the surface material. The scale bar is 1 millimeter (0.04 inch).
Credit: NASA/JPL-Caltech/University of Arizona


Formation of a martian dust devil captured at the surface of Mars by NASA’s Spirit Rover. Fine dust is ubiquitous in the martian environment.
Credit: NASA/JPL

The atomic force microscope maps the shape of particles in three dimensions by scanning them with a sharp tip at the end of a spring. During the scan, invisibly fine particles are held by a series of pits etched into a substrate microfabricated from a silicon wafer. Pike’s group at Imperial College produced these silicon microdiscs.

The atomic force microscope can detail the shapes of particles as small as about 100 nanometers, about one one-thousandth the width of a human hair. That is about 100 times greater magnification than seen with Phoenix’s optical microscope, which made its first images of Martian soil about two months ago. Until now, Phoenix’s optical microscope held the record for producing the most highly magnified images to come from another planet.

"I’m delighted that this microscope is producing images that will help us understand Mars at the highest detail ever," Staufer said. "This is proof of the microscope’s potential. We are now ready to start doing scientific experiments that will add a new dimension to measurements being made by other Phoenix lander instruments."

This image shows the particles of dust captured by Phoenix and viewed under the optical microscope. To the right is a 3-D representation of the sample as seen by Phoenix’s Atomic Force microscope, which has a magnification 100x greater than the optical microscope.
Credit: NASA/U of Arizona/Imperial College London

"After this first success, we’re now working on building up a portrait gallery of the dust on Mars," Pike added.

Mars’ ultra-fine dust is the medium that actively links gases in the Martian atmosphere to processes in martian soil, so it is critically important to understanding Mars’ environment, the researchers said.

The fine details that this technology can yield concerning the surface of Mars can help scientists understand if the planet is, or ever was, a suitable habitat for microbial life. The technology is also proof that robotic microscopy can be used to explore other planets. Similar techniques could one day help researchers search for evidence of life in our solar system.

The particle seen in the atomic force microscope image was part of a sample scooped by the robotic arm from the "Snow White" trench and delivered to Phoenix’s microscope station in early July. The microscope station includes the optical microscope, the atomic force microscope and the sample delivery wheel. It is part of a suite of tools called Phoenix’s Microscopy, Electrochemistry and Conductivity Analyzer.

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