One reason researchers spend so much time and effort looking for meteorites is that they’re a window into our solar system’s deep past. The oldest of these space rocks contain materials that are unchanged from the time billions of years ago when a disk of gas and debris orbited the sun, later coalescing into the planets. Now, researchers have found something even more enlightening inside one meteorite: a miniscule bit of what they believe is a comet containing grains of stardust that existed before our solar system began.
Hannah Osborne at Newsweek reports that the speck of suspected comet comes from a meteorite called LaPaz Icefield 02342—collected in Antarctica in 2002 and believed to have formed beyond Jupiter about 4.5 billion years ago. During its formation, it picked up a tiny bit of the presolar comet, only about a tenth of a millimeter across. The find is detailed in the journal Nature Astronomy.
While asteroids and comets both form from the disk of dust, gas and debris surrounding a young star, they coalesce at different distances from the star and have a different chemical makeup explains Ryan F. Mandelbaum at Gizmodo. Comets are usually composed of more water ice and carbon. Asteroids come in many different flavors, but are composed of metals and rock. LaPaz Icefield 02342 is a primitive carbonaceous chondrite meteorite that has not weathered much since falling to Earth.
While bits of asteroid bombard the Earth fairly frequently, fragments of comet are much harder to come by. That’s why researchers were pleasantly surprised to discover the tiny bit of comet while analyzing LaPaz.
“When Larry [Nittler] and Carles [Moyano-Cambero] showed me the first electron images of the carbon-rich material, I knew we were looking at something very rare,” co-author Jemma Davidson, a meteorite expert at Arizona State University says in a press release. “It was one of those exciting moments you live for as a scientist.”
Though the fragment is incredibly small, lead author Larry Nittler of Carnegie Institution of Science says it tells a complex story. “It helps us understand a bit better how material came together to form the planets when the solar system was a giant rotating disk of gas and dust around the forming Sun. It tells us that as carbon-rich icy bodies were forming in the far outer reaches of the disk, some of their building blocks moved closer to the Sun and got trapped in asteroids,” he tells Osborne.
Even more important, he says that because the grains of comet were trapped inside the meteorite and protected from heat and weathering, their ancient chemical signature has been preserved much better than it otherwise would. “It gave us a peek at material that would not have survived to reach our planet's surface on its own, helping us to understand the early solar system's chemistry,” he says in the press release.
The smidge of comet is also important for understanding the formation of Earth. It’s believed that most of the water on our planet was deposited by comets and asteroids. Meteorite researcher Matthew Genge of Imperial College London, not involved in the study, tells Osborne that this fragment shows that the material that formed comets, believed to form on outer reaches of the proto-solar system, was pulled into the inner solar system, explaining how water may have been transported to Earth 4 billion years ago.