Scientists had a first-hand test of the poorly understood near-subsurface physical characteristics of rubble-pile asteroids when NASA's OSIRIS-REx probe retrieved samples from the surface of the asteroid Bennu in 2020.
According to recent research, the layer under the asteroid's surface is made up of loosely bonded rock shards that have twice as much empty space as the whole asteroid.
New insights on asteroid Bennu
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According to Dr. Kevin Walsh of SwRI, who is also the lead author of a paper about this research that was published in the journal Science Advances, the low gravity of rubble-pile asteroids like Bennu weakens its near-subsurface by not compressing the upper layers and minimizing the influence of particle cohesion, as per ScienceDaily.
Experts drew the conclusion that Bennu should have a low density, weakly bound subsurface layer as a general characteristic, not only one that is restricted to the contact point.
Bennu is a spheroidal collection of debris and rock pieces that is 1,700 feet in diameter and kept together by gravity, thus fitting its classification as a rubble-pile asteroid.
It is believed to have developed as a result of a collision with a bigger main-asteroid-belt item.
Since being freed from its much bigger parent asteroid some millions or billions of years ago, it has led a harsh life as seen by the rocks that are dispersed throughout its extensively cratered surface.
The OSIRIS-REx mission's objective is to gather and return at least 60 grams of surface material from Bennu to Earth in 2023.
OSIRIS-REx stands for Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer.
Additional insights were gained through sample gathering efforts.
Walsh claimed that scientists working on the OSIRIS-REx mission have thus far assessed Bennu's thermal characteristics and craters to determine the density and porosity of individual rubble-pile asteroids.
It has not yet been explicitly investigated how the collection of particles, or regolith, at an asteroid's surface controls and influences long-term development.
Although NASA calculates that between 2175 and 2199, there is a 1 in 2,700 probability of a collision, Bennu is still one of the deadliest asteroids known to exist.
Additionally, it is believed by scientists that many asteroids have a structure akin to a "rubble pile" made up mostly of conglomerations of rock, gravel, and soil held together by weak gravitational forces.
The sample experiment at Bennu demonstrated that it's nearly difficult to foresee how an impact may affect such a mound of rubble.
According to Walsh, the touchdown gave the player their first actual experience pushing anything into the ground.
"And we would need to know what the surface is like if we ever went and really tried to deflect anything like this," he said, "so that it doesn't just absorb the hit," as per Space.
Planetary scientist Dante Lauretta, head of the OSIRIS-REx mission at the University of Arizona
In addition, Lauretta noted that the material underneath the surface of Bennu seemed redder than the planet's bluish surface, which showed that the exposed space rocks are eroded by cosmic rays and other types of space weather.
Researchers who are seeking to understand the beginnings of life on Earth are very interested in the reddish colors because they suggest that organic substances like hydrocarbons may be present inside the asteroid.
The priceless material won't be available to the researchers until OSIRIS-expected REx's arrival in September 2023.
The probe managed to gather around nine ounces (250 grams) of asteroid dust during the spectacular sample effort, which is four times more than the researchers needed for the analysis but a little less than they had hoped for, according to Lauretta.
Apophis is another dangerous asteroid that OSIRIS-REx will visit in 2029 after dropping off its cargo at Earth next year thanks to a new extension of the mission.
