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The tumultuous past of a ‘golf ball asteroid’

Researchers have discovered new details revealing the history of 'golf ball asteroid' Pallas.Pallas Researchers (custom credit)

Researchers have developed images of a “golf ball asteroid” that may help piece together the tumultuous history of an object that is following an unusual orbit in the asteroid belt.

Researchers analyzed 11 series of images taken over two periods in 2017 and 2019, uncovering a pockmarked, golf ball-like surface.

In a paper published in Nature Astronomy on Monday they didn’t explain the rock’s strange, tilted path that makes it an outlier among the other asteroids, but they suggested the heavily cratered surface might be the result of a demolition derby-like path through the asteroid belt.

“From these images, we can now say that Pallas [the asteroid] is the most cratered object that we know of in the asteroid belt,” Michael Marsset, a Massachusetts Institute of Technology postdoctoral researcher and the lead author of the study, told MIT News.


“We’re seeing a new world for the first time,” MIT professor Richard Binzel, Marsset’s supervisor, said in a telephone interview. “This is one of the largest asteroids that has been very elusive to explore because of its tilted orbit.”

Pallas, discovered in 1802 and named after the Greek goddess of wisdom, is the third largest object in the asteroid belt and about one-seventh the size of the moon. Since its discovery, the asteroid’s path has puzzled astronomers because of its inclined trajectory.

Because of its path, the international team of researchers believes, Pallas experiences high-velocity impacts with other asteroids two to three times more often than Ceres, the largest object in the asteroid belt, and Vesta, the second largest asteroid in the belt. The team used simulations of impacts that the three asteroids would have experienced over the past four billion years — nearly the age of the solar system — and compared them. Every time Pallas, Ceres, or Vesta had an impact crater of at least 40 kilometers, the team recorded it.


“Its tilted orbit is a straightforward explanation for the very weird surface that we don’t see on either of the other two asteroids,” Marsset said.

When the findings were revealed and comparisons to a golf ball were made, Binzel said he was struck with awe by the resemblance. But when he expressed his excitement to Marsset about it, “I had to explain, because Michael is French, what a golf ball is,” he said, laughing.

The team found 10 percent of Pallas’s surface to be covered with craters. Dozens of them were roughly one-fifth the size of the impact on Earth that likely caused the dinosaurs’ extinction 65 million years ago.

This is “suggestive of a violent collisional history,” the researchers said in their paper.

Led by French researcher Pierre Vernazza, the team used the SPHERE, a powerful telescope used to find planets, at the European Southern Observatory’s Very Large Telescope in the mountains of Chile. They made two additional discoveries while studying the asteroid, including a bright spot in Pallas’s southern hemisphere and an impact crater along its equator estimated to be about 400 kilometers in diameter.

The researchers believe a large salt deposit caused by a mixture of water, ice, and silicates that melted in the asteroid’s interior and hydrated the silicates could have been exposed during an impact, creating the bright spot.

Through simulations, the team found the large crater at the equator was likely created by an impact with an object between 20 and 40 kilometers wide about 1.7 billion years ago. Fragments likely broke off upon impact, matching some smaller pieces that are currently orbiting Pallas.


“People have proposed missions to Pallas with very small, cheap satellites,” Marsset said in the article. “I don’t know if they would happen, but they could tell us more about the surface of Pallas and the origin of the bright spot."

Matt Berg can be reached at Follow him on Twitter @mattberg33.