Science Adores a Vacuum – A report by Kevin Lizarazo

Science Adores a Vacuum

By Andrew Goldstein

Space is generally described as a void. It isn’t. Micrometeoroids smaller than the lead of a mechanical pencil speed through the cosmos. The sun constantly emits a solar wind of electrons, protons and alpha particles. Anything floating through our solar system is constantly barraged by both.

Earth’s atmosphere and magnetic field shield the planet, but airless bodies like asteroids and the moon are ever changing on some scale because of space weathering. Space weathering is a physical wear-and-tear these bodies go through when they’re hit by micrometeoroids and solar wind. This darkens their color and makes it difficult to see just what they are made of.

Scientists argue as to whether micrometeoroid bombardment or solar wind plays a more important role in the process of space weathering. To help answer that question, planetary scientists at Stony Brook University are planning to mimic the process of space weathering, using a small, specially built vacuum box and one of the brightest lights on Earth, an X-ray beam generated by a giant particle accelerator at Brookhaven National Laboratory.

“When we look at different bodies from Earth, we only see the information coming from the surface, but the surface has been processed a lot chemically. We want to study these processes in the laboratory.  We want to simulate that surface and energetic particle interaction in the laboratory,” said Mehmet Yesiltas, a Turkish postdoctoral researcher who was on a government fellowship in Stony Brook.

To do that, Yesiltas and his mentor, Timothy Glotch, an associate professor of geosciences, designed a cube that could keep samples in vacuum conditions while they are exposed to simulated versions of both solar wind and micrometeoroid bombardment. The cube can retain the vacuum while researchers analyze how the samples are affected.

They did this as part of  a program called RIS4E (or Remote In Situ and Synchrotron Studies for Science and Exploration) led by Glotch. One goal of the project is to work on getting accurate readings of the moon and asteroids using far away, or remote, sensing tools. Another goal is to develop tools and techniques to make the most of samples that may be brought back in future space exploration.

These vacuum cube experiments could show how solar winds and micrometeoroid bombardment affect airless bodies in space both individually and collectively. The cube would help refine remote sensing, so that future missions to airless bodies can know what different space rocks are made of and where to send astronauts to get the best samples.

The 8-inch steel vacuum cube Yesiltas designed has three thin, strong sapphire windows, with a movable stand inside on which to place rock samples. The cube is connected by a door to a smaller vacuum chamber where samples are inserted. While the samples face one window, researchers will shoot them with a laser calibrated to imitate the energy of one micrometeoroid. Then, they will move the sample to the second window to take a picture of it using high resolution X-ray imaging. They will see how the space weathering affects the way infrared (IR) analyzing tools see samples. The images can then be stacked, laser exposure after laser exposure, to make a high-quality video of changes that happen micrometeoroid by micrometeoroid.

“We can do one shot with the laser, and then take X-ray and IR spectra. Then we can take another shot with the laser and take an IR and X-ray spectra. And we can do a third shot – boom, boom, boom – ad infinitum until either the samples look like they’re stopping changing or we reach a point that we’re satisfied that we have enough information,” Glotch said.

To get the highest resolution, without letting any air leak into the vacuum and contaminate the samples, the window facing the X-ray camera could only be 4 millimeters thick. Taking their time to ensure the vacuum held, the engineers of MDC Vacuum delivered the tube months later than expected to the RIS4E lab.

Creating this unique device took more time than anyone expected. After spending a year and a half designing the vacuum cube chamber, Yesiltas was called back to Turkey. The cube was still in its computer design phase.

“It hurt a little bit, coming back to Turkey without having done any experiments over there but that’s what I had to do,” Yesiltas said. “I was anxious to see the chamber and perform the first experiment with it, but I couldn’t because my fellowship required me to go back and I couldn’t extend my stay any more.”

Carey Legett, a geosciences graduate student, was asked to take over the vacuum cube project. At the time, Legett was working on computer modeling the effects of space weathering on lunar and airless body soils, the same effects Yesiltas and Glotch were trying to clarify.

“It dovetailed perfectly into what I was doing. There was an initial period where it was really hard because they had two years’ worth of work into this where they had all of these discussions about how things were going to work and decisions were made, and I come in with a completely outside view of how this project is working.”

While transitioning, Legett would spend hours discussing the design with Yesiltas and Glotch. He advised them to reroute the wiring and ground the device differently to keep the samples safer.

After receiving and inspecting the cube, the RIS4E team transported it to the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory. There, it will be run by Juergen Thieme, head of the Submicron Resolution X-ray (SRX) beamline. This is a full three years since the beginning of design.

NSLS-II accelerates electrons to 99.996 percent the speed of light, and uses their energy to create incredibly bright X-rays that create pictures of incredibly small samples. The SRX beamline has a resolution of 50 nanometers per pixel. If an iPhone 7 camera had that kind of resolution, each picture would only be able to show about four and a half red blood cells.

Starting in September, another post-doc is joining the team  specifically to work on the beamline with the vacuum cube project. According to Thieme, her addition to the team will help speed up the process to put the cube to use with the beamline. RIS4E should start getting results by the end of the year.

(Carey Legett of SBU Department of Geosciences)