An armoured asteroid? Yes, NASA says it exists and can reveal secrets of our solar system

The NASA OSIRIS-REx spacecraft closely observed the armoured asteroid 101955 Bennu, which has been touted to reveal the secrets behind the birth of our solar system.

Observing the primitive armoured asteroid called 101955 Bennu, the NASA OSIRIS-REx is now very close to completing its mission that will reveal the past of our solar system. (NASA)

It has been almost six years since the NASA OSIRIS-REx spacecraft first took its flight towards a very special target. Unlike most NASA missions, it was not going for a planet or a moon but a 450-metres wide asteroid known as 101955 Bennu. The objective of this unusual mission was to collect at least 60 grams of sample from this asteroid and bring it back to Earth. Why? Because scientists believe that this asteroid could be the key to unlocking the past of our solar system. While the spacecraft will not make its touchdown to Earth till 2023, it has revealed something even more interesting about asteroid Bennu. Apparently this primitive asteroid is also covered with a body armour. Read on to know more.

The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) spacecraft was launched on September 8, 2016. In September 2017, flew past the Earth and in 2018, it finally reached Bennu. After spending around two years analysing the surface to find a suitable site to extract a sample, it finally collected between 400g and one kilogram of sample. Ever since then, it has been observing various other traits of this asteroid and it has made some remarkable discoveries.

NASA OSIRIS-REx finds a strange armour on asteroid Bennu

During regular observations, NASA astronomers tried to calculate the age of the asteroid as one of the main reasons behind this mission was that the asteroid was considered to be very primitive. While without testing the sample, it is not possible to accurately determine its age, scientists have figured out a unique method to find out how old a celestial object is and it revolves around their impact craters.

“Planetary scientists can estimate the age of surfaces by measuring the abundance and sizes of craters. Impact craters accumulate over time, so a surface with many craters is older than a surface with few craters,” NASA explained in a post. “Also, the size of the crater depends on the size of the impactor, with larger impactors generally making larger craters. Because small meteoroids are far more abundant than large meteoroids, celestial objects like asteroids usually have many more small craters than large ones,” it added.

However, observing Bennu, this pattern did not make sense for the smaller craters. Scientists observed that craters smaller than 2-3 metres decreased in number as the size decreased. This unusual behaviour initially perplexed NASA researchers as it meant that the asteroid was younger than they first believed.

But after studying the asteroid more, they found that the asteroid is made up of debris of a larger asteroid and is just a giant “rubble pile”. Now, scientists believe that the existence of these small boulders have prevented the crater formation from smaller meteoroids.

“The displacement or disruption of an individual or small group of boulders by a small impact is probably one of the most fast-acting processes on a rubble-pile asteroid's surface. On Bennu, this contributes to making the surface appear to be many times younger than the interior,” said Edward (Beau) Bierhaus of Lockheed Martin Space, lead author of the paper around Bennu's age.