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The asteroid Bennu could have been dwelling to historic water flows

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Perhaps as a prelude to that effort, the researchers published a series of new studies on Bennu's geochemistry in Science and Science Advances today, providing some of the greatest revelations to date. Here are the most compelling ones.

Bennu's watery story

In the first scientific study, scientists used high-resolution images from OSIRIS-Rex as well as spectroscopy (which analyzes electromagnetic waves emitted by Bennu to determine chemistry) to better understand the composition and history of the nightingale crater region of the asteroid where the sample was is collected.

They found that boulders in this area showed bright veins that were narrow but about three feet long, similar to other carbonaceous chondritic meteorites that have landed on Earth. In these cases, the veins indicate that the rock had once interacted with running water.

For Bennu, of course, the veins indicate that water flowed through this asteroid very early in the history of the solar system, says Hannah Kaplan, planetary researcher at NASA's Goddard Space Flight Center in Maryland and lead author of the study. Given the size of the veins, the researchers estimate that there was "a system of fluid flow that stretched for miles" when Bennu was part of a much larger parent body. These water flows could have lasted for up to millions of years. Similar phenomena are likely to have occurred in many other carbonaceous chondritic asteroids.

Carbon, carbon everywhere

Another scientific study used infrared spectroscopy to show how prevalent carbonaceous minerals and hydrated clay minerals were on Bennu's surface. According to Amy Simon, planetary researcher at NASA's Goddard Space Flight Center and lead author of this study, these minerals are found all over Bennu (although they are particularly focused on certain boulders). This is very good news as it means “we should find both (materials) in our returned samples,” she says.

Scientists believe that Bennu was created from the debris of a collision his parent's body underwent in the main asteroid belt of our solar system. The remains, which came together as Bennu, soon migrated into orbit closer to Earth. According to Simon, this process could be one way that tiny asteroid bodies deliver organics and hydrated minerals to the inner solar system, where they later became part of planets like Earth.

Rare rocks abound

A study published in Science Advances used infrared cameras to examine the boulders and rocks that make up Bennu's debris pile structure. The results show that two types of rocks are common on Bennu, but one type is much more porous and more brittle than rocks on Earth, the Moon, or Mars. "It is likely that we do not have similar specimens in meteorite collections on Earth as Bennus rocks are likely too weak to survive entry into the atmosphere," says Ben Rozitis, a researcher at the Open University in the UK and Lead author of this study. "It is likely that OSIRIS-REx will bring back asteroid samples that scientists have not previously examined in the laboratory."

Weathering of the elements

Things in space can weather just as much as on earth – only out there, solar winds and granular matter such as micrometeorites are the main forces to be reckoned with. Daniella DellaGiustina, a scientist at the University of Arizona, led a scientific study examining signs of this weathering in Bennu.

As it turns out, weathering is an odd process for Bennu. While most other asteroids and the moon darken (or redden) with weathering, Bennu actually gets lighter (or bluer). "It shows us that something on Bennu's surface is very different from other planetary objects that we have observed," says DellaGiustina. The darker the surface on Bennu, the better this area should be preserved. It just so happens that Nightingale is one of the darkest areas of Bennu, which means it could be an undisturbed record of some of the oldest activities in the solar system.

Weak gravity game

Another study in Science Advances focused on characterizing Bennu's weak gravitational field by observing the movement of OSIRIS-REx in the asteroid's orbit and the behavior of pebble-sized debris grains ejected from its surface. The measurements suggest that the asteroid's debris pile is unevenly distributed along its surface and is particularly light at the asteroid's equator. These data make sense in models that suggest Bennu had a period of rapid rotation at some point in his history (a hypothesis supported by another Science Advances study examining Bennu's hemispherical asymmetry) .

"Although the current measurements do not finally solve all of our questions about the development of debris pile asteroids, they significantly limit the range of options and will bring our future theoretical and in-situ investigations more into focus," says D.J. Scheeres, aerospace engineer at the University of Colorado, Boulder, and lead author of the study.

Scheeres adds that the study also validates a novel research technique for assessing the gravitational field of a small body by examining the particles it emits. Future missions to other asteroids can now build on this method and try to make it faster and more accurate.

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Steven Gregory