Eighteen years after the return to Earth of the NASA Stardust mission that brought the first samples of the famous comet, the true nature of this icy object is becoming clear.

Stardust collected material from Wild 2, a comet that likely formed beyond Neptune and currently orbits the Sun between Mars and Jupiter. Painstaking analysis of microscopic samples recently described in a journal GeochemistryHaving been working on Stardust samples for several years, St. Ryan Ogliore, a professor of physics at Washington University in St. Louis, said it revealed a surprising fact about the comet’s origin and history.

When Stardust was launched in 1999, many scientists expected the comet’s rocky material to consist of the primordial dust that formed the Solar System (the “stardust” that gave the mission its name).

But real samples told a different story: Wild 2 contained a mixture of dust created by various events early in the solar system’s history. For Ogliore, it was exciting to discover that Wild 2 contained recordings of “local” events. “The comet witnessed the events that shaped the solar system into the shape we see today,” he said.

The comet, which spent most of its life in the cold storage of space, avoided the heat and water changes seen in asteroid samples.

Unique composition of Wild 2

“Comet Wild 2 contains things we’ve never seen in meteorites, such as unusual carbon-iron assemblages and precursors to the igneous spheres that form the most common type of meteorite,” said the McDonell Center’s Ogliore. for space sciences. “And all these objects are perfectly protected in Wild 2.”

Nearly two decades later, it would seem that scientists have had plenty of time to analyze the tiny amount of material returned from the Stardust mission: less than a milligram (think a grain of sand). But this material is dispersed into thousands of tiny particles in a pizza-sized collector. “Almost every part of Wild 2 is unique and has a story,” Ogliore said. “Extracting and analyzing these grains takes a lot of time. But the gain for science is huge.”

Much of Wild 2 remains unexplored and undoubtedly holds many more surprises. Over time, samples may be examined using new methods that were not available when the mission was started.

“Samples of stardust, which are microscopic grains taken from objects less than two miles across, contain records of the deep past spanning billions of kilometers,” Ogliore said. “After studying this comet for 18 years, we have a much better picture of the dynamic formation years of the Solar System.”