#EBSstory Asteroid Bennu’s samples investigated at the ESRF

The asteroid Bennu is a scientific gem. Asteroids are airless remnants left over from the early formation of our solar system about 4.6 billion years ago. Early analysis led by NASA has indicated that asteroid Bennu appears to be very rich in carbon and shows evidence for hydration, which scientists believe can shed light on the origin of life and the Solar System.

“It is a primitive carbonaceous asteroid, a so-called near-Earth object located within the asteroid belt between Mars and Jupiter and, because it hasn’t undergone the geological processes known for example from Earth and other planets, we think its composition can provide us with clues about the beginning of the Solar System”, says Dr. Beverley Tkalcec, lead scientist in the team at ESRF and geoscientist at the Goethe University Frankfurt and specialised in space samples.

After the return of the OSIRIS-REx mission, NASA sent out samples of the asteroid to  scientists across the world for further investigation, including long-term ESRF users from the Goethe University Frankfurt (Germany) and University of Ghent (Belgium). They have come to the ESRF this week to  analyse some of the precious samples on the high-energy ESRF beamline ID15A. “The targeted  minerals in our samples are less than half a millimetre in size and the concentration of some of the elements we want to find is of the range of  parts per million”, explains Laszlo Vincze, professor from the University of Ghent and leading the synchrotron analysis of the samples.

The researchers want to track and quantify individual minerals enriched with Rare Earth Elements (REE), as tracers of asteroidal processes. These minerals might have changed after being in contact with water. “It is like finding a needle in a haystack, so we need a really high flux to study these samples and this is exactly what the ESRF offers today with the new EBS”, adds Vincze. The experiments use X-ray fluorescence combining high incident energies of 90 keV with a 300 nm resolution scanning capability and a new high-count rate high-efficiency fluorescence detector.

At ID15A, the scientists first scan the samples as a whole, which are, for example, about 150x350 microns in size (for reference, a human hair is about 75 microns). Once they have mapped it, they zoom into the areas of particular interest for more detailed analysis.

This is not the first time that the team is at the ESRF with asteroid samples brought to Earth in space missions. For the last three years, they have been studying samples from the Ryugu asteroid brought to Earth in December 2020 by the Japanese Hayabusa2 mission. The results, which were published in Science in 2022, showed the history of the asteroid. “Ryugu and Bennu are very similar, even if Ryugu is double the size of Bennu, but the findings of Ryugu can certainly guide us in our search for elements on Bennu”, explains Tkalcec.

These investigations build up on a series of studies by this team at the ESRF spanning over almost two decades, investigating cometary and interstellar material returned by NASA’s Stardust mission.

Text by Montserrat Capellas Espuny

Top image: The asteroid Bennu. Credits: NASA