Just before he gets ready to fire a projectile down the 14-foot barrel of a vertical gun, planetary scientist Peter Schultz turns to me and gives an apologetic smile.
“There’s something you have to do,” he says, as his graduate student snickers. “You have to assume the Gault position.”
The Gault position, it turns out, involves crossing your index finger over your middle, your ring finger over your pinkie, then crossing your two arms over one another and finally crossing your legs (while standing). Schultz assumes it, explaining that it serves as a good luck measure, as does his graduate student and the other engineers in the gun control room. I comply, as does WIRED photographer Ariel Zambelich.
“We’re armed,” someone calls. “Voltage looks good.” A klaxon buzzes and, seconds later, there’s the sound of a powerful explosion from the next room over. A burst of flame and sand appears on the computer screen in front of us and, just like that, the NASA Ames Vertical Gun range has provided a new data point for science.
The gun is a fantastic tool for studying the effects of meteorite impacts on different places in the solar system. You see, Earth is something of an anomaly. Most other rocky bodies are covered in countless craters ranging from the size of continents down to the size of sand grains. The active tectonics of our planet recycle its crust, erasing the long-term scars that come from living in a solar system full of debris. But just about every other terrestrial planet, moon, asteroid, and comet is coated in pockmarks, a testament to how pervasive and important impacts have been in our solar system’s history.
Over the course of its nearly 50-year career, the gun range been used to figure out why the scars of an impact look different on Mars than they do on Venus. It has helped explain how the man on the moon could have gotten his face. And it has provided key data for many NASA missions, in particular the Deep Impact spacecraft, which shot a projectile into an asteroid.
Peter Schultz, who teaches geoscience at Brown University, has done much of this research. He’s worked at the gun range for 33 years, becoming its principal investigator in 2012, and he knows a great deal about its history and lore.
Donald Gault (front), who helped design and build the Ames Vertical Gun Range, stands with William Quaide (on ladder) back when the facility was new. Image: NASA
Though it’s called a gun, the facility doesn’t look much like any firearm you’ve ever seen. The main chassis is a long metal barrel as thick as a cannon mounted on an enormous red pole that forks at the end into two legs. The red pole was once used to hold MIM-14 Nike-Hercules missiles that served as an anti-ballistic defense against Soviet nuclear warheads, Schultz explains. This complex is pointed at a huge rotund cylinder and can be moved up and down in 15-degree increments to simulate a meteorite strike at different angles. The entire machine is housed in a 3-story industrial building here at NASA’s Ames campus.
At the far end of the barrel, a gunpowder explosion is used to compress hydrogen gas to as much as 1 million times atmospheric pressure. The compressed gas gets released and sent down the launch tube, firing a projectile pellet at speeds between 7,000 and 15,000 mph. The shot enters the cylinder, in which low pressure or even a vacuum is maintained, and hits a dish filled with different material that simulates whatever planetary body researchers are studying. High-speed cameras mounted on windows around the cylinder record the impact aftermath at up to 1 million frames per second.
The origin of both the facility and the odd position I was compelled to take stem from planetologist Donald Gault, who designed and used the range to study impacts on the moon. Built in 1965, the gun range helped interpret information returned from the Ranger probes, which crashed into the lunar surface during the Apollo era. Scientists weren’t sure of the exact composition of the regolith at the time and needed to know before attempting to land people there.
“There were reports at the time that it was going to be really, really fluffy,” said Schultz. “There was one document that said the astronauts would land and then sink out of sight.”
Using data from the gun, Gault helped figure out that the Apollo astronauts weren’t going to die by lunar quicksand. After NASA finished its goal of safely landing and returning astronauts, Gault continued using the gun range to study the formation of craters on the moon. When he retired, NASA planned to mothball the gun but an outcry from the planetary science community re-opened the firing range as a national facility. It was during this time that Schultz, who had worked with Gault as a post-doc, was hired to take over as science coordinator for the gun range.
The day WIRED visited the gun, Schultz and his graduate student, Stephanie Quintana, were simulating meteorite impacts on Mars. Inside the facility’s vacuum chamber was a large gray dish full of dolomite powder, standing in for the Martian surface.
Schultz and Quintana were investigating how a meteorite explosion could create a dust and vapor shockwave that would form a vortex with speeds three to four times that of a tornado, inflicting serious damage. The researchers had already used satellite images to identify telltale scars (.pdf) around real impact craters on Mars. Though they had some ideas, how exactly these frozen wind streaks formed remained a mystery.
Schultz explained that they would be firing a quarter-inch Styrofoam pellet into the dolomite powder and watch the ensuing outburst. He’s easy to talk to, genial, energetic, and quick to divulge interesting tidbits of information on meteorite impacts that reveal his breadth of knowledge on the topic.
Two different-looking impact craters on two different planets. A small unnamed crater on Mars is seen at top while Addams crater on Venus is seen at bottom. Images: 1) NASA/JPL/ASU. 2) NASA
“The situation on Mars is totally different from what would happen on Venus,” he said. The thin Martian atmosphere allows for ejecta from an impact to spread out far and wide in all directions. But Venus’ crushing atmospheric pressure holds in the vapor, preventing it from expanding and acting “like a pressure cooker,” he said. When a meteorite hits Venus, the dust and debris condenses under the pressure and rains down as molten silica which then flows out from the crater, creating long and beautiful deposits that trail away from the impact site.
In the middle of this impromptu interplanetary impact comparison course, another one of Schultz’s students, Megan Bruck Syal, tells him that data from one of their instruments is in. It’s the spectrometer, which they will use to analyze the ball of gas and vapor created during their simulated Mars surface impact.
“Oh, you got it!” Schultz said, rubbing his hands together like a kid expecting candy. He glances at the spectra, whoops, and then sings a few bars of “We’re in the money.” “Hot damn,” he said. “Those are nice and sharp.”
It’s clear that Schultz brings this same passion for scientific discovery into every experiment he does. He explains one test he conducted years ago in which he fabricated transparent spheres and then shot a projectile into them to watch how a shockwave evolves inside a planetary body.
The interesting twist came when he simulated meteorite coming in at an angle to the surface, a process known as an oblique impact. With a high-speed camera, Schultz watched how the shockwave from an impact hitting at a tangent of around 30 degrees propagated forward. The vibrations spread out from the initial impact site and then converged on the other side of the sphere, but not directly opposite the crater.
“I applied this to understanding how you make the man in the moon,” he said.
On the lunar far side is one of the biggest impact craters in the solar system, the South Pole Aitken Basin, which would stretch halfway across the U.S. if it were on Earth. Schultz has suggested that the enormous rock that hit the moon billions of years ago to form that crater may have come in at an oblique angle.
Using computer models, he calculated that the shockwave could have circled around to the moon’s near side, causing a 10-minute tremor. Cracks would have appeared in the surface, opening and closing, and cracking again. This could have created something like a pump that allowed magma to rise to the lunar surface, which erupted as lava that covered huge areas known as the Mare Imbrium and Oceanus Procellarum, major nearside features that humans have gazed at for millennia.
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