Before the arrival of NASA’s visiting spacecraft OSIRIS-REx in late 2018, scientists predicted that Bennu’s surface would be totally or partially covered with a fine regolith of sand and pebbles. The REx in OSIRIS-REx stands for Regolith Explorer, which is what the REx in OSIRIS-REx stands for. OSIRIS-REx, on the other hand, discovered Bennu’s surface to be littered with boulders and huge rocks. Scientists stated this month on October 21, 2021, that they may have found an explanation to the boulder puzzle of asteroid Bennu.
The University of Arizona conducted the new research, which will be published in the peer-reviewed journal Nature on October 6, 2021. The lack of fine regolith on Bunnu’s surface may be attributed to permeable rocks, according to the research.
On Bennu, thermal radiation, also known as heat radiation, assisted scientists in distinguishing between fine regolith and bigger pebbles and boulders. A heated surface emits thermal radiation in every direction. Bennu, whose orbit around the sun is in the same region of the solar system like Earth’s (thus the term “near-Earth asteroid”), goes a little closer to the sun than Earth does. Bennu is an ancient Egyptian mythical bird connected with the sun, creation, and rebirth. Bennu, like Earth, receives heat from the sun. Scientists were able to solve the boulder enigma due to the re-emitted heat radiation.
It aided because fine regolith has different heat radiation than bigger boulders. Thermal emission is controlled by the particle size in fine regolith. The porosity of the rock, however, regulates this emission in bigger rocks.
The researchers built a library of thermal emission samples based on various combinations of fine regolith and porous rocks for their testing. The machine-learning algorithm then joined the samples together. This method was used to estimate 122 places on Bennu, both during the day and at night.
Researchers were taken aback by the findings. The fine regolith was not only strewn throughout the asteroid’s surface at random. Instead, there was a rise of many tens of percent in the few regions where the rocks are non-porous. It was, however, lower in very porous rock locations.
This suggests that Bennu’s permeable rocks create very little regolith, according to the researchers. This is because meteoroid strikes compress the rocks rather than shatter them. The spaces in the rocks function as a cushion, protecting them from the blows. In essence, the rocks shield themselves from collisions to some extent.
The findings are consistent with other asteroids and illustrate variances between asteroids of different sorts. For example, Ryugu, like Bennu, is a B-type carbonaceous asteroid. It is similarly coated in porous rocks and is devoid of fine regolith. The Hayabusa2 mission in Japan produced those results.
Itokawa, a stony S-type asteroid visited by the previous Hayabusa mission in 2005, on the other hand, contains a lot of fine regolith on its surface. Recent research indicated that its rocks are less permeable than those on Bennu and Ryugu, which is consistent with that.
Bennu is a leftover of the solar system’s creation. On its surface, OSIRIS-Rex discovered signs of hydrated minerals. This alludes to ancient water, most likely on Bennu’s bigger parent body. Bennu is hypothesized to hold organic chemicals, the precursors of life, on its surface since it is carbon-rich.
OSIRIS-Rex has returned to Earth. The sample return capsule, with valuable Bennu samples, is set to land on September 24, 2023.