NASA and Japan reveal the unknown features of the Bennu and Ryugu asteroids

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Bennu belongs to potentially dangerous asteroids and although it is little more than half of an astronomical unit on Earth (about 75 million kilometers), it could have an impact

Asteroids are the "building blocks" with which the planets were formed and those that failed to be part of one of the eight bodies of our solar system travel through space, as in the case of Bennu, whose investigators have now described unexpected features: its surface is a scree.

This is one of the conclusions of NASA's OSIRIS-REX mission, with Spanish participation, which on 3 December 2018 arrived in Bennu with the objective of characterizing it and, in the future, of bringing samples of its surface (it is expected that reach the Earth in 2023).

The description of this asteroid subsequently, in astronomical terms, our planet is published in seven articles in various magazines of the Natura group.

This is data collected in the first observations of the NASA probe, when it was about seven kilometers from Bennu; it is now less than a kilometer from its surface and soon the OSIRIS-REX team will release more details.

However, these first images already reveal unknown features, referring to Efe Javier Licandro, of the Canary Islands Astrophysics Institute (Spanish archipelago in the Atlantic) and signatory of one of the works.

The observations suggest that Bennu is older than expected – has an estimated age of between one hundred million and one thousand millions of years– and probably originated in the main asteroid belt area of ​​the solar system that is located between the orbits of Mars and Jupiter – according to the summary of the journal Nature.

For Licandro, the most surprising thing was to note that its surface is a scree: "we expected to find a body covered with dust or particles of centimeters but we saw that it is covered with stones larger than a meter and at least one of 30 meters. "

"We believe these should be very porous", describes Licandro, who points out that the stones are subjected to an important thermal stress due to the temperature differences between day and night, which cause them to break more easily.

The discovery that it is a gravel provides clues to how Bennu was formed and confirmed – this idea has already been explained – that this is the result of the breaking of a larger object and the subsequent grouping of pieces.

Moreover, it has also been seen that Bennu hardly reflects 4% of the light it receives, but in some rocks this percentage rises to 15%, which could indicate a different and non-homogeneous composition of its rocks.

Bennu and other asteroids that have not undergone great changes in its structure since its formation, represent the remains of the formation of the Solar System, therefore the information of its surface, form and other properties are essential to know the different phases of the 39 evolution of our planetary system.

But not only. They are also important from the astrobiological point of view to understand the origin and the evolution of life on Earth: these bodies, which clashed in the course of their history against our planet, contain water and a complex organic that has allowed the formation of oceans in the past and the development of life on Earth, says Licandro.

Furthermore, there is security. Bennu belongs to the asteroids potentially dangerous and although it is a little more than half of an astronomical unit of the Earth – about 75 million kilometers -, it could have an impact.

That's why it's important to study and monitor it, because, although the odds are low, they do exist. And an impact could cause catastrophes of different magnitude depending on where it clashes.

In another study published in Science, the scientists of the University of Tokyo and the Hayabusa 2 mission publish the data of the Ryugu asteroid, which, although resembles the "brother" of Bennu, shows some different characteristics, including it contains much less water and is much drier than expected by experts.

The presence of dry asteroids in the belt asteroids could change the models used to describe the chemical composition of the first solar system, according to its authors.

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