Asteroid Bennu was once part of a space rock with flowing water

OSIRIS-REx and Bennu

An illustration of NASA’s OSIRIS-REx spacecraft descending in direction of the asteroid Bennu

NASA/Goddard/College of Arizona

The asteroid Bennu is an odd little place, however knowledge from NASA’s OSIRIS-REx mission is beginning to unravel its mysteries. The spacecraft, which has been orbiting Bennu since December 2018, is gearing as much as take a pattern from the asteroid’s floor later this month. In preparation, it has gathered a smorgasbord of data, together with hints that Bennu’s guardian asteroid could have had flowing water.

Bennu is a kind of asteroid referred to as a rubble pile, shaped when one thing smashed into a bigger asteroid billions of years in the past and the bits coalesced into many smaller asteroids. By finding out Bennu, which is about 500 metres huge, we will study extra about this guardian asteroid, which was in all probability a couple of hundred kilometres throughout.


When OSIRIS-REx reached Bennu, it noticed one thing unusual: a number of the boulders had shiny veins as much as 150 centimetres lengthy and 14 centimetres thick. These veins are too giant to have shaped on Bennu itself, says Hannah Kaplan at NASA’s Goddard Area Flight Middle in Maryland, in order that they had been in all probability parts of bigger cracks on Bennu’s guardian that had been as much as a number of kilometres lengthy.

“They counsel that there was fluid flowing on pretty giant scales on Bennu’s guardian asteroid,” says Kaplan. That’s as a result of the veins are product of carbonates, a kind of compound that usually types attributable to interactions between water and rock, she says.

In actual fact, over 98 per cent of Bennu’s floor appears to be coated in carbonates and natural molecules, advanced carbon-bearing compounds which are seen as precursors to life. But regardless of in all probability having each water and organics, Bennu’s guardian was unlikely to be teeming with life.

“You’re within the vacuum of house, there’s no environment, you’re a number of irradiation, it’s chilly – you wouldn’t need to sit on the floor,” says Kaplan. “It’s not a beneficial surroundings per se, but it surely does have a number of the components that make a spot technically liveable.”

One of many foremost targets of OSIRIS-REx is to analyze the carbon on Bennu as a result of Earth was in all probability constructed from rocks just like it, and these could have brought the ingredients of life right here. “These similar varieties of organics could have been delivered to early Earth and should have been the beginning of a number of the natural chemistry that led to life as we all know it,” says Kaplan.

There are additionally variations throughout the surface of Bennu which are onerous to elucidate. It’s lined in boulders, however the largest ones are principally in its southern hemisphere. The boulders themselves are unusual too, with some being so porous that vacant house seems to comprise as much as 55 per cent of them, greater than any meteorite we’ve got ever recovered.

There appear to be two populations of rocks: porous, darker-coloured ones and denser, lighter-coloured ones that always have carbonate veins. These variations aren’t apparent to the human eye – the floor would simply appear to be a reasonably uniform dark-grey to us – however they might be vital in serving to us determine how Bennu shaped. They might have come from two totally different areas in Bennu’s guardian physique, with the denser rocks coming from deeper underground.

That wouldn’t reply all of Bennu’s mysteries, although, as a result of some relate to the asteroid’s evolution after it was chipped off its bigger guardian physique. “The way in which Bennu’s color modifications over time is sort of a bit totally different than what we’ve got seen on different planetary surfaces just like the moon or different asteroids that we’ve visited,” says Daniella DellaGiustina on the College of Arizona.

Astronomers can date totally different areas of Bennu by evaluating brisker areas twith extra weathered ones, revealing how they modify over time. Rocks on Bennu appear to grow to be extra blue, whereas those on other space rocks are inclined to grow to be extra purple. This can be due to how these carbonate-filled rocks work together with the photo voltaic wind and micrometeorites in a different way to rocks with out carbonates, says DellaGiustina.

On 20 October, OSIRIS-REx will take a small pattern from Bennu’s floor earlier than heading again in direction of Earth. When the pattern will get right here in 2023, researchers will have the ability to experiment with them immediately, hopefully answering many of those questions.

“All of the characterisation work we’ve finished for Bennu mainly places this return pattern into context,” says Benjamin Rozitis on the Open College within the UK. If we will research the pattern completely and perceive the way it pertains to the totally different rocks on Bennu, that makes it simpler to match Bennu with different asteroids and small our bodies.

“We are able to’t do a pattern return from each fascinating place within the photo voltaic system, however by finding out Bennu globally and making an attempt to know it as a small world, we get a a lot better sense of how Bennu pertains to different objects in our photo voltaic system that we’d by no means have the ability to pattern,” says DellaGiustina.

Journal references: Science, DOI:10.1126/science.abc3557, DOI:10.1126/science.abc3660, DOI:10.1126/science.abc3522;
Science Advances,
DOI:10.1126/sciadv.abd3649, DOI:10.1126/sciadv.abc3699, DOI:10.1126/sciadv.abc3350

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