Space Rocks Hit Ceres With a Splat

It’s hard to do experiments in space.  It costs a boatload of money, takes years of preparation, and even then we can’t get much further than low-Earth orbit. But there is a cheaper alternative to understanding the universe.  We can perform experiments on Earth to simulate what happens far beyond our own planet.

Experiments using a high velocity cannon suggest that when asteroids hit targets that are icy or made of porous silicate materials, much of the impact material stays in the crater. The findings have implications for the surface composition of the dwarf planet Ceres. Credit: NASA Ames Research Center / Brown University

That’s just what scientists did at the Vertical Gun Range at NASA’s Ames Research Center in California.  They found that Ceres is likely a mish-mash of celestial bodies from several billion years of bombardment.

Until March of this year, when the Dawn spacecraft entered orbit of the nearest dwarf planet, we didn’t really know what Ceres was made of.  Measurements of the density of the icy rock reveal that it is either made from light and porous material, or it contains a significant amount of water.  Whatever the case, one certainty is that Ceres is a boring, cratered rock.

“It’s really bland in the telescopic observations,” said Terik Daly, a Ph.D. student at Brown and the study’s lead author. “It’s like someone took a single color of spray paint and sprayed the whole thing. When we think about what might have caused this homogeneous surface, our thoughts turn to impact processes.”

Using NASA’s Vertical Gun Range, a cannon with a 14-foot barrel that can launch projectiles at up to 16,000 miles per hour, the researchers found materials that simulated the two leading possibilities for the make-up of Ceres’ crust: Porous Silicate vs. Icy.

For Porous Silicate, they used powdered pumice, while the icy rock was represented by snow and snow covered by a thin veneer of fluffy silicate material, to simulate the possibility that Ceres’ ice sits below a silicate layer. Pebble-sized bits of basalt and aluminum, simulating both stony and metallic meteorites.

In both cases, the impactor seemed to stick to the body, though it was more prominent in the icy case. “We show that when you have a vertical impact into snow — an analog for the porous ice we think might be just beneath the surface of Ceres — you can have about 77 percent of the impactor’s mass stay in or near the crater,” said Daly.

Impactors tend to stick to the surface if they are coming in at a sufficiently slow speed, but in the case of Ceres, it seems that average and above-average speed impactors are sticking too.  This makes it difficult if you want to get a surface sample of Ceres, since most of the surface would be covered with foreign material.  You would have to look for a fresh impact in hopes that deeper material native to Ceres would have been blasted out.

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