This ancient stardust is the oldest ever to be examined in a lab

Tiny grains give insight into galactic happenings before our solar system’s birth

Egg nebula stardust

Bits of dust expelled by aging stars (like those in the Egg Nebula plume, pictured) and brought to Earth on a meteorite are the oldest ever dated in a lab. One 8-micrometer grain is also shown.

Background: W. Sparks/STSCI and R. Sahai/JPL-NASA; Inset: Courtesy of J.N. Avila

Ancient stardust extracted from a meteorite contains specks that are up to about 3 billion years older than the solar system, making them the oldest solids ever dated in a lab, researchers report.

Unlike most of the other stardust that went into building our solar system, these microscopic grains have remained intact since they were shed by aging stars billions of years ago. The exotic makeup of the silicon carbide grains, from a meteorite that landed in Australia more than 50 years ago, tipped scientists off that the minerals were older than the solar system (SN: 11/22/19).

Measuring levels of neon-21 in dozens of grains revealed how much older. Neon-21 is a form of the chemical element that builds up when silicon carbide is bombarded with high-energy particles called galactic cosmic rays in interstellar space. The higher a grain’s neon-21 concentration, the longer it must have drifted in space before being embedded in a hunk of space rock during the solar system’s formation 4.6 billion years ago.

The oldest grains are estimated to be around 7 billion years old, some 2 billion to 3 billion years older than the solar system, researchers report online January 13 in the Proceedings of the National Academy of Sciences. Before this analysis, the oldest stardust dated in a lab was estimated to predate the solar system by about 1 billion years.

Such old stardust grains can serve as time capsules that provide clues about goings-on in the Milky Way from before the sun’s birth. For instance, in addition to the few extremely old grains, the new study uncovered a surprising number of grains that formed less than 300 million years before the solar system. That glut of relatively younger dust probably came from an especially high number of stars reaching the late, dust-releasing stage of their lives around that time. The finding suggests that there was a “baby boom of star formation” in the galaxy a couple of billion years before that, says coauthor Philipp Heck, a cosmochemist at the Field Museum of Natural History in Chicago and the University of Chicago.  

“Using these microscopic dust grains to tell us something about large-scale events in the presolar history of our galaxy is pretty cool,” says Larry Nittler, a cosmochemist at the Carnegie Institution for Science in Washington, D.C., not involved in the work.

Finding and dating more extremely old dust grains lodged in meteorites may give scientists a more complete picture of the Milky Way’s history even further back in time.

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