Article Dans Une Revue Nature Année : 2025

An evaporite sequence from ancient brine recorded in Bennu samples

T J Mccoy
S S Russell
S A Singerling
F E Brenker
N E Timms
W D A Rickard
S. Ray
Z. Gainsforth
G. Dominguez
A J King
H. Yurimoto
S A Eckley
P A Bland
  • Fonction : Auteur
T R Ireland
N V Almeida
H C Bates
P F Schofield
L B Seifert
N. Sakamoto
N. Kawasaki
F. Jourdan
S M Reddy
D W Saxey
I J Ong
B S Prince
L R Smith
M C Benner
N A Kerrison
L R Wardell
T R Rose
  • Fonction : Auteur
T. Salge
L. Le
V M Tu
  • Fonction : Auteur
Z. Zeszut
C. Mayers
  • Fonction : Auteur
X. Sun
D H Hill
V E Hamilton
D P Glavin
J P Dworkin
H H Kaplan
I A Franchi
K T Tait
S. Tachibana
H C Connolly
D S Lauretta

Résumé

Evaporation or freezing of water-rich fluids with dilute concentrations of dissolved salts can produce brines, as observed in closed basins on Earth 1 and detected by remote sensing on icy bodies in the outer Solar System 2,3 . The mineralogical evolution of these brines is well understood in regard to terrestrial environments 4 , but poorly constrained for extraterrestrial systems owing to a lack of direct sampling. Here we report the occurrence of salt minerals in samples of the asteroid (101955) Bennu returned by the OSIRIS-REx mission 5 . These include sodium-bearing phosphates and sodium-rich carbonates, sulfates, chlorides and fluorides formed during evaporation of a late-stage brine that existed early in the history of Bennu's parent body. Discovery of diverse salts would not be possible without mission sample return and careful curation and storage, because these decompose with prolonged exposure to Earth's atmosphere. Similar brines probably still occur in the interior of icy bodies Ceres and Enceladus, as indicated by spectra or measurement of sodium carbonate on the surface or in plumes 2,3 .

Brines (over 3.5 wt% dissolved solids) are environments in which life could have evolved or might persist in the Solar System 6 , and are targets for spacecraft exploration. Evaporation or freezing can lead to the formation of brines from which a variety of minerals (for example, carbonates, sulfates and halides) precipitate. On Earth, such mineral deposits are a major source of technologically critical elements 7 . On Mars, brine freezing points extend to approximately -20 °C, prolonging the liquid state of water 8 . Icy outer Solar System bodies contain subsurface brines, sometimes as oceans. Evidence of subsurface brines is found on Saturn's moon Enceladus 9 and the dwarf planet Ceres 3 , the largest body in the asteroid belt.

Our knowledge of brines beyond Earth is hampered by a lack of samples. Remote-sensing observations of Mars, Ceres and Enceladus limit our ability to determine precipitated phases in minor to trace abundances, unravel the age and timing of fluid evolution and precipitation and determine the compositions of the associated fluids. Evaporite phases known from meteorites are extremely limited. These include sulfates and halides in Martian nakhlites 10 , intrusive igneous rocks that experienced secondary alteration, and potentially indigenous halite in ordinary chondrites 11 .

Early analyses of samples from Bennu recorded evidence of pervasive aqueous alteration-including hydrated phyllosilicate clay minerals.

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hal-04922948 , version 1 (31-01-2025)

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T J Mccoy, S S Russell, T J Zega, K L Thomas-Keprta, S A Singerling, et al.. An evaporite sequence from ancient brine recorded in Bennu samples. Nature, 2025, 637 (8048), pp.1072 - 1077. ⟨10.1038/s41586-024-08495-6⟩. ⟨hal-04922948⟩
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