Samples from comet Wild 2 reveal surprising past

Eighteen years after NASA’s Stardust mission returned to Earth with the first samples of a known comet, the true nature of this icy object is beginning to reveal itself.

Stardust collected material from Wild 2, a comet that likely formed beyond Neptune and currently orbits the sun between Mars and Jupiter. Careful analyzes of microscopic samples, recently described in the journal Geochemistryrevealed a surprising truth about the comet’s origins and history, said Ryan Ogliore, associate professor of physics in arts and sciences at Washington University in St. Louis, who has been studying Stardust samples for several years.

When Stardust launched in 1999, many scientists expected that the comet’s rocky material would be dominated by the primordial dust that built the solar system – the “stardust” that gave the stardust its name. assignment.

But the actual samples told a different story: Wild 2 contained a potpourri of dust formed from different events early in the solar system’s history. For Ogliore, the discovery that Wild 2 contained a recording of “local” events was exciting.

“The comet witnessed the events that shaped the solar system as we see it today,” he said.

Kept in the cold chamber of space for most of its life, the comet avoided the heat and water alteration seen in asteroid samples.

“Comet Wild 2 contains things we’ve never seen in meteorites, like unusual assemblages of carbon and iron, and the precursors of the igneous spherules that are the most common type of meteorite,” Ogliore said. “And all of these items have been beautifully preserved in Wild 2.”

After nearly two decades, it may seem that scientists have had plenty of time to analyze the tiny amount of material returned by the Stardust mission: less than a milligram (imagine a grain of sand). However, this material is distributed into thousands of tiny particles on a collector the size of a pizza.

“Almost every particle in Wild 2 is unique and has a different story to tell,” Ogliore said. “Extracting and analyzing these grains takes a long time. But the scientific results are enormous.”

Most of the particles in Wild 2 have not yet been studied and are sure to have many more surprises in store. Over time, the samples can be studied using new techniques that did not exist when the mission launched.

“Stardust samples, microscopic grains from a body less than three kilometers wide, contain traces of a deep past spanning billions of kilometers,” Ogliore said. “After 18 years of interrogating this comet, we have a much better view of the dynamic formative years of the solar system.”