Maria Valdes hadn’t celebrated Asteroid Day before, but this year she was an enthusiastic participant.

       “I have to say this is the most exciting way to celebrate your first Asteroid Day,” the postdoctoral student said.

       The center of attention this Asteroid Day — a day set aside to raise awareness of the risks of asteroid impacts — was a cream-colored sphere, larger than a baseball, with grooves and markings all the way around.

       It’s a 3D printing of the Field Museum’s newly classified meteorite, or a fallen space rock, from the asteroid Vesta — the brightest and the second largest in the asteroid belt. The asteroid belt is a doughnut-shaped ring of debris that orbits the sun between Mars and Jupiter.

       An actual piece of the meteorite, a gray rock that sparkles with sides glittering with a glassy black crust, sat next to the replica piece of Vesta at a presentation celebrating the discovery of the rare acquisition.

       Maria Valdes, a postdoctoral researcher studying meteorites, holds a model of the asteroid Vesta on June 30, 2021, at the Field Museum. (Brian Cassella / Chicago Tribune)

       This piece of Vesta, the first from the minor planet that the Field Museum has had, was found in the Sahara desert and procured from a private meteorite collector, Terry Boudreaux, who frequently donates his findings to the Field Museum. The museum was able to buy this meteorite from Boudreaux in late 2020. After working under Pritzker Curator of Meteorites Philipp Heck, Valdes was able to classify it as part of Vesta.

       The shadowy outlines of the terrain in Vesta's northern region are seen in this image from NASA's Dawn spacecraft on Sept. 5, 2012. The view looks down at the asteroid's north pole, which is in the middle of the image. (NASA)

       Vesta, as the second largest asteroid, is about 330 miles across, and is differentiated, meaning that it has a core, mantle and crust like Earth does. This makes studying parts of Vesta a good way to understand Earth since scientists cannot take parts of Earth to look at its core, Valdes and Heck said.

       Studying asteroids and meteorites is important as it shows what the early solar system looked like, because it is uniquely unencumbered by time.

       “There are really like two directions you can take the study of meteorites, and one is to study early solar system history to get a clearer idea of what the early solar system looked like,” Valdes said. “The other is to understand our own planet, actually. Unlike on Earth, where our early history has largely been overprinted by geological processes, asteroids ... have not undergone the same sort of geological overprinting. Their histories are really frozen in time, they have pristine records of early solar system history. So by studying asteroids, we really get a clear idea of how the Earth came to be, how it was processed and why it looks the way it does today.”

       “When we want to learn more about how the solar system was formed, we go to meteorites,” Heck added. “It’s from the earliest time when after planets (were) formed, and it’s like a time capsule, it hasn’t been opened or changed since it formed.”

       Maria Valdes holds pieces of a meteorite identified as coming from the asteroid Vesta on June 30, 2021, at the Field Museum. (Brian Cassella / Chicago Tribune)

       After the museum acquired the meteorite in late 2020, Valdes began to study it via CT scans — similar to the ones medical professionals use — to determine where they should cut the rock open at the best angle to expose the surface. After being cut, the rock was taken to be scanned by an electron microscope to create a chemical map, or a 3D recreation of the meteorite. From there, the two scientists determined the kind of rock they were studying, and Valdes compared it to other meteorites to figure out which asteroid it was part of.

       Valdes found it to be a perfect match for Vesta.

       That was a rare finding because although Vesta is the second largest in the belt, only about 4% of meteorites studied come from it, Valdes said.

       “There was a chance that I could classify it and it would be really boring,” she said.

       Typically, the Field Museum and Heck work with meteorites that have already been classified. This is Valdes’ first classification of a meteorite.

       “We were so excited,” Heck said. “We were jumping up and down. I popped open a bottle of champagne for the occasion.”

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