Three mysterious jets of particles emitted by the asteroid Bennu, and closely observed by the American probe Osiris-Rex, show that this fossil of the Solar System is an active asteroid with complex internal dynamics. This is what is indicated by the analysis of data from the NASA mission published in the journal Science by the researchers coordinated by Dante Lauretta, of the American University of Arizona, in Tucson.
Bennu is a small spinning top-shaped asteroid with a diameter of about 500 meters and is probably a 'pile of fragments' held together by their own gravity. In December 2018, it was joined by the Osiris-Rex probe that also speaks Italian with the technology that allows it to orient itself thanks to the stellar sensor built by the Leonardo group in Campi Bisenzio, and which aims to capture a sample from the surface of Bennu ( by 2020) to bring it back to Earth by 2023.
Since the beginning of 2019, the probe has taken a picture of the asteroid in order to select the sampling site. Analyzing the collected images, the researchers identified a cloud of particles around the asteroid, identifying three main expulsion events in early 2019, during which some particles remained in Bennu's orbit for days before falling back to the surface, while others were thrown into space. The cause still remains mysterious, however scholars have hypothesized that the phenomenon could have been generated by the impact of small meteorites or by the fracture of the surface due to thermal stress.
The discovery, according to Jessica Agarwal, of the Max Planck Institute for Solar System Research at Göttingen, "shows that an apparently inactive asteroid can host complex internal dynamics that affect the surface, with implications that are still unknown for its evolution". The first active asteroid, capable of periodically emitting gas and dust, was discovered in 1996 and since then about twenty have been identified. For Agarwal "discovering the processes underlying this activity is important for understanding the evolution of these celestial bodies and how they release dust in interplanetary space".