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ETH Zurich isotope study ties asteroid Bennu to Ryugu and CI meteorites

First reported 24 Oct, 12:50 UTCSource: ScienceDaily Space & Time + 1 moreLast editorial activity 24 Oct, 12:50 UTCWrite a comment ↓

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Isotope measurements on material from the asteroid Bennu point to a chemical kinship with the asteroid Ryugu and a rare group of primitive meteorites. Reported in Science Advances, the work suggests Bennu took shape where material from the inner and outer Solar System blended, with Jupiter having an unexpected hand in it.

Samples arrive at an ETH Zurich laboratory

NASA's OSIRIS-REx mission flew to Bennu, gathered material from its surface and returned the samples to Earth in 2023. A capsule holding roughly 120 grams touched down in the Utah desert on September 23 of that year, after which scientists around the world were sent small portions of the cargo for close study.

Maria Schönbächler, Professor of Isotope Geochemistry at ETH Zurich, received half a gram of Bennu material for her laboratory. Her team set to work straight away, scanning the samples for traces of the asteroid's past.

Isotopes link Bennu with Ryugu and CI meteorites

The ETH Zurich researchers measured isotopes of iron, titanium and chromium. Isotopes are variants of one element that differ in neutron count and therefore in mass, and their proportions can reveal where an body's building blocks originated and, at times, when they came together.

The measurements showed iron and titanium spread almost uniformly through Bennu's material. They also exposed a close chemical bond between Bennu, Ryugu and a scarce family of primitive meteorites called CI meteorites, which are carbon-rich fragments of the early Solar System that have changed little in billions of years and are exceptionally rare among meteorites found on Earth. All three carry strikingly similar isotopic signatures, pointing to a shared pool of ancient cosmic dust as their source.

A revised picture of Bennu's birthplace

The findings call earlier theories about Bennu's origin into question. According to the reported results, Jupiter helped shape the material from which Bennu and other ancient objects were built, and the asteroid appears to have formed where inner and outer Solar System matter mixed.

Bennu circles the Sun roughly every 1.2 years and comes relatively close to Earth about every six years, within roughly 300,000 kilometres, a proximity that makes it well placed for detailed study.

Open questions

Which processes moved material from different regions of the early Solar System into Bennu's source reservoir?
Will independent laboratories reproduce the isotope patterns reported by the ETH Zurich team?