[ad_1]
In just a few days, NASA will bounce its OSIRIS-REx probe off the asteroid Bennu. The mission will collect a sample of the asteroid and return it to Earth for further study, one of the first missions of its kind.
That return sample will help us understand not only asteroids, but also the early days of the Solar System’s existence. However, that is not the only mission of OSIRIS-REx.
The probe reached Bennu’s orbit in December 2018 and has since been using its suite of instruments to learn everything it can about the asteroid ahead of its long-planned encounter.
And boy, has he ever done it. Six separate articles just appeared in the magazines Sciences Y Scientific advances detailing Bennu’s physical properties and how they reveal a surprisingly complex story.
“The spacecraft has been observing the asteroid for almost two years,” said astronomer Joshua Emery of Northern Arizona University and a member of the OSIRIS-REx science team. “Bennu has turned out to be a fascinating little asteroid and it has given us many surprises.”
Bennu is what’s known as a ‘debris pile’ asteroid, which is exactly what it sounds like: a relatively loose, low-density conglomerate of rock, believed to have formed when a larger object broke apart, and at the less part of the material. they came back together. In Bennu’s case, the shape he formed is a rough diamond, with a pronounced ridge at the equator.
Now, for the first time, we have a detailed 3D digital terrain map of the asteroid, led by Michael Daly of the University of York. This reveals that the equatorial crest is not alone; other much more subtle ridges run from pole to pole, indicating that although the asteroid is made of debris, it does have some internal cohesion.
In recent years, we’ve had hints of other weird things going on on the Diamond B (i.e. Bennu).
Last year, we discovered that Bennu was ejecting material from its surface, some of which fell back and some of which appeared to enter stable orbit. And the scientists found evidence of carbonaceous material that hinted at the presence of water at some point in Bennu’s mysterious past.
A new global spectral study of the asteroid in infrared and near infrared, led by Amy Simon of NASA-Goddard, has confirmed the presence of organic and carbon-containing materials, spread across the surface of Bennu, the first concrete detection of such things. . on a near-Earth asteroid. This is consistent with the hypothesis that asteroids and meteorites could have brought at least some of the ingredients for life to Earth.
Once there was also water
But the asteroid’s carbon content has a more detailed story to tell. A detailed spectral study has revealed glowing streaks of carbonate material running through a series of rocks.
This, according to a team of scientists led by Hannah Kaplan of NASA-Goddard, is consistent with carbonates found in “water-altered carbonaceous chondrite meteorites” – carbonates that were formed through interactions with water.
Some of these veins are one meter long and several centimeters thick. This, the researchers say, is evidence that water once flowed freely over rocks, an asteroid-scale hydrothermal system that was once present in the main body that later gave birth to Bennu.
“The flow of fluid in Bennu’s parent body would have occurred at distances of kilometers over thousands or millions of years,” the researchers wrote in their paper.
Multispectral images of the surface revealed that Bennu is unevenly degraded in an analysis led by Daniella DellaGiustina of the University of Arizona. Using false-coloration visible light images of the asteroid, the team found that some regions have been exposed to weather events such as cosmic rays and the solar wind for longer than others, suggesting processes, such as impact events, that expose material. cool at different times. .
The region of the Nightingale crater, where the probe is going to retrieve a sample, is a cooler material, meaning it will provide a cleaner view of things in the early Solar System, when Bennu is believed to have formed.
And there is more. A study of temperature changes led by Ben Rozitis of the Open University found something interesting about the rocks at Bennu. They are divided into two types: stronger and less porous, and weaker and more porous. The strongest boulders are those with carbonate streaks, suggesting that interaction with water can ultimately produce stronger rocks as liquid seeps material into the holes.
But the weaker boulders are also interesting. They are unlikely to survive entry into Earth’s atmosphere as they would heat up and explode, which means they are likely a type of space rock that we haven’t had a chance to study closely before.
Finally, we return to the aforementioned ejected rocks. We still don’t know exactly how they are ejected from the asteroid, but the way they fly up and down is a surprisingly useful tool for probing the interior of the asteroid.
“It was a bit like someone was on the surface of the asteroid and threw these marbles so they could track them,” said study leader Daniel Scheeres of the University of Colorado Boulder. “Our colleagues were able to infer the field of gravity in the trajectories that these particles took.”
When combined with the gravity field measurements taken by the OSIRIS-REx in orbit, the team was able to compile an interior density profile of the asteroid, as the denser regions create a stronger local gravity field.
And they found something surprising. They thought that the asteroid would have roughly the same density throughout its path; but it seems denser on the surface. The least dense regions are the equatorial crest and the core of the asteroid, as if it had a great vacuum inside.
Since the asteroid’s rotation accelerates over time, this means that eventually, it is likely to separate.
However, that is a long way to go. For now, the asteroid will have to be content with a kiss from a probe in the crater. And these new analyzes have given researchers a framework within which to interpret the careful study of that sample, when it finally reaches Earth.
The six articles, published in Sciences Y Scientific advances, it can be found here, here, here, here, here and here.
