Bennu's evaporite minerals confirm liquid water moved through the early solar system's building blocks

Harold Connolly Jr., the OSIRIS-REx mission’s sample science lead, described Bennu’s returned material as potentially rich in evaporite minerals. The peer-reviewed record now bears that out in detail.

A paper published in Nature confirms the presence of evaporite minerals, including trona and other sodium carbonate compounds, in the Bennu samples collected by OSIRIS-REx. Independent coverage from EurekAlert, Phys.org, and The Conversation places the formation of those minerals at more than 4.5 billion years ago, when ancient salty brines pooled, circulated, and then evaporated inside the asteroid’s parent body. What remained, preserved in the rubble that eventually became Bennu, is a mineral record of liquid water chemistry from the earliest chapter of the solar system.

Evaporites form through a specific and well-understood process: water carrying dissolved salts reaches a surface or near-surface environment, evaporation concentrates the solution, and the dissolved material precipitates out as solid mineral deposits. On Earth, the process produces structures as familiar as salt flats and as economically significant as potash deposits. Finding the same class of minerals in a carbonaceous asteroid tells scientists that the process operated not just on planets but in smaller, undifferentiated bodies during the solar system’s first few hundred million years.

The asteroid samples could be rich in evaporate minerals Harold Connolly Jr.

The significance runs deeper than confirming that water existed somewhere in the early solar system. Bennu is a well-studied near-Earth asteroid of the type associated with carbon-rich, primitive material: the kind of body that planetary scientists believe delivered organic compounds and water to the early Earth. If bodies like Bennu were actively cycling liquid water and precipitating salts, the chemistry available for delivery to rocky planets was more varied and potentially more prebiotic than models assuming only dry or ice-bearing asteroids would allow.

The Nature findings also carry methodological weight. Returned samples offer a level of analytical access that remote sensing and meteorite studies cannot match. Meteorites are contaminated by atmospheric entry and terrestrial exposure; remote observations are limited by spectral resolution and surface representation. The OSIRIS-REx sample return, which brought back material sealed from the space environment, gives researchers a ground truth for interpreting the broader population of carbonaceous asteroids. The evaporite identification is an early result from what will be years of continued analysis on those materials.

Connolly Jr.’s framing of the samples as potentially rich in evaporite minerals reflects his direct involvement in planning and executing the science return from the mission. The Nature paper and the associated coverage represent the published confirmation of findings his team was positioned to pursue from the moment the sample capsule landed. What the peer-reviewed record adds to that framing is precision: specific mineral identifications, formation ages anchored at 4.5-plus billion years, and a mechanistic account of how briny water moved through the parent body before Bennu’s current form existed.

The broader implication, supported by the published findings, is that water-mediated chemistry was not confined to the wet inner planets of the early solar system. It operated in the small-body population, left a mineral signature that survived intact for billions of years, and is now recoverable in a terrestrial laboratory. That is a different picture of solar system history than the one researchers worked with before sample return, and the evaporite record is one of the cleaner pieces of evidence behind it.