Bennu: Journeying to an asteroid's core

Typically, meteorites encountered on Earth are subject to re-entry heat and surface contamination, but the Bennu sample appeared unaffected
The image is an illustration of an asteroid. — Pixabay
The image is an illustration of an asteroid. — Pixabay

Addressing the American Geophysical Union assembly in San Francisco, Dante Lauretta likened the moment to a reunion with an old acquaintance after "seven years and a journey of 3 billion miles." He recounted the sight before him in Utah's desert on September 24th — a capsule resembling a charred, worn washing-machine drum. 

This capsule, packed and sent into space from Cape Canaveral in the summer of 2016, had made its way to Bennu, a small asteroid intersecting Earth's orbit, as part of the OSIRIS REx mission.

After collecting around 140g of material from Bennu's surface in 2020, the spacecraft cast off the capsule and diverted its attention to studying another asteroid, Apophis. Despite a glitch in its descent — failing to deploy its parachute as planned — the capsule safely reached the Earth's surface, much to Lauretta's relief.

During the assembly on December 11th, Lauretta shared some initial findings from the capsule's analysis. Most notably, the sample proved to be pristine — a rare occurrence in the realm of asteroid material. Typically, meteorites encountered on Earth are subject to re-entry heat and surface contamination, but the Bennu sample appeared unaffected.

This pristine nature is crucial as asteroids like Bennu are considered the solar system's primordial remnants, preserving elemental compositions similar to the young sun. Thus, the sample represents a valuable reservoir of ancient material, providing insights into the solar system's early formation.

Beyond elemental analysis, researchers are intrigued by the variation in rock types and mysterious crust coatings found on some grains within the sample. This complexity promises years of further investigation.

Additionally, the capsule's re-entry provided an opportunity for infrasound observation, aiding scientists in understanding meteorite impacts and potentially seismic activity on other planets. This research could prove invaluable for future planetary exploration efforts, such as studying Venus's seismic activity.

While the skies of Venus won't be filled with infrasound-sampling balloons anytime soon, scientists recognise the value of seizing opportunities for comprehensive data collection. Moreover, repurposing one mission's unintended consequence as a testbed for another adds an extra layer of intrigue to scientific inquiry.