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The asteroid Vesta weathers differently than any other researched moon or asteroid, according to a recent analysis by Carle Pieters, professor of geological sciences, and other investigators for NASA's Dawn Mission. The findings, published Nov. 1 in the journal Nature, shed light on the weathering process by which the surface of Vesta changes with exposure to the sun and other minerals. 

Dawn was the first mission to capture high-resolution photos of the surface of Vesta, the second largest asteroid in the asteroid belt. According to the new findings, Vesta differs from other airless bodies like the Moon because it does not accumulate iron droplets as it ages. This accumulation is what makes the face of the Moon appear darker than Vesta. Instead, Vesta undergoes a small-scale mixing of particles that does not involve iron coatings.

Pieters and her team predicted that Vesta might weather differently after observing telescopic images of the asteroid. Vesta's bright colors are a "spectral fingerprint" that makes the asteroid unique, according to Lucy McFadden, co-investigator for the Dawn Mission and a scientist at the Goddard Flight Space Center. But for the past 60 years, why Vesta appeared different remained a mystery to scientists, McFadden said. Before Dawn, they "argued for decades" about why Vesta appeared immune to the type of space weathering that occurs on the moon, Pieters said.

But Dawn was the first opportunity to use high quality data to begin answering that question. The findings suggest that different types of processes occur on airless bodies. 

The new research "expands our understanding of what we look for," said David Blewett, an author of the paper who works in the Johns Hopkins University Applied Physics Laboratory. Scientists had previously assumed that all surfaces weathered like the moon does. Pieters said she believes it is now worth revisiting the weathering of the moon and other asteroids because Dawn's recent findings "give us new criteria" on how surfaces alter in space. 

These findings will affect many other researchers in planetary science through a "ripple effect" because now many models of processes in space will have to take into consideration the different types of weathering, according to Beth Ellen Clark Joseph, a professor of physics at Ithaca College who was not involved in Pieter's research.

"One of the most exciting things of a mission like Dawn is that you're seeing the surface for the first time ever," said Tom McCord, a co-investigator for the Dawn Mission and director at the Bear Fight Institute. Dawn's images dazzled investigators with incredible amounts of new information, going from a "light in the telescope to an actual world you can imagine walking on," Blewett said. 

The Dawn spacecraft has left Vesta and is now moving towards Ceres, the largest asteroid in the belt. But scientists are not done with Vesta. Data from a sophisticated instrument like the Dawn spacecraft requires a good deal of processing before the conclusions are clear. Pieters's paper is just the first step in analyzing all the new information on Vesta. "We're not just sitting down twiddling our thumbs now," Blewett explained, "there's analysis that will go on for a long time." Scientists now have the challenge of using raw data to explain some of Vesta's other phenomena. "It becomes sort of a detective investigation," McCord said.  

Though Pieters has more work ahead of her, she praised the poetic aspects of space exploration. "Everything we learn about the other planets helps us understand what's happening here as well." Pieters concluded that this makes her discoveries "far away, but still close to home."


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