Asteroid Bennu’s brittle boulders could make sample-grabbing simpler

When NASA’s OSIRIS-REx arrived at near-Earth asteroid Bennu, scientists have been dismayed to discover a floor lined with hazardous-looking boulders.

However new analysis means that these boulders are surprisingly brittle. That’s probably excellent news for the spacecraft, which is charged with grabbing a bit of Bennu on October 20 and returning it to Earth in 2023 (SN: 1/15/19). If the rocks are crumbly, that might decrease the chance of damaging the spacecraft’s tools.

That type of rock additionally could also be too fragile to outlive the journey by Earth’s ambiance with out burning up. If that’s the case, scientists could also be near getting their fingers on a never-before-seen type of area rock, researchers report in a group of papers printed October Eight in Science and Science Advances.

Information taken from Earth earlier than OSIRIS-REx launched instructed that Bennu’s floor could be sandy. So it was a shock to discover a tough panorama strewn with boulders when the spacecraft arrived in 2018 (SN: 12/3/18).

“We had actually satisfied ourselves that Bennu was a clean object,” says Daniella DellaGiustina, a planetary scientist on the College of Arizona in Tucson and member of the OSIRIS-REx crew. “As everybody noticed from the primary footage, that was not the case.”

The crew discovered a comparatively clear crater, nicknamed Nightingale, from which to retrieve a pattern of the area rock (SN: 12/12/19). Nonetheless, the fear stays that the boulders may pose a security hazard for the sampling system, which was designed to deal with pebbles just a few centimeters throughout.

From late April by early June 2019, planetary scientist Ben Rozitis of the Open College in Milton Keynes, England, and colleagues mapped the best way Bennu’s boulders retain warmth, a clue to the rocks’ construction. Denser supplies maintain warmth higher than finer-grained ones, like how a sandy seashore cools rapidly after sunset, however single massive rocks stay heat.

This map exhibits the place carbon-bearing minerals (represented by redder colours) are positioned on Bennu’s floor. The chance to research these minerals may assist scientists work out how carbon received to the early Earth.A. Simon et al/Science 2020Based mostly on these maps — and maps of different floor properties, described within the collection of papers launched October 8 — Bennu’s boulders appear to return in two flavors: darker-colored rocks which can be weaker and extra porous and lighter-colored, denser rocks which can be stronger and fewer porous. Even the denser rocks are rather more porous and brittle than meteorites from comparable asteroids which were discovered on Earth. The least dense meteorites are about 15 % porous; Bennu’s rocks appear to be between 30 and 50 % porous, Rozitis and colleagues discovered.

“That is thrilling,” says DellaGiustina, a coauthor of the brand new papers. The spacecraft and its devices may “encounter some boulders on the pattern web site which may in any other case be tough to ingest,” she says, however “in the event that they’re porous and weak, then they may simply break down,” making them simpler to gather.

The lighter, denser rocks additionally look like shot by with veins of carbonate, which means that they have been within the presence of flowing water sooner or later of their previous (SN: 12/10/18). NASA selected Bennu as an asteroid to go to partly as a result of it resembles carbonaceous chondrite meteorites, which scientists suppose are time capsules of the early photo voltaic system. Related area rocks may have delivered water and natural supplies to Earth billions of years in the past.

However Bennu’s extra porous rocks look like not like something in scientists’ present assortment of meteorites, Rozitis says. “This is among the cool issues about OSIRIS-REx — it’s fairly possible it would decide up new materials that isn’t in our meteorite assortment,” he says.

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That’s plausible, says meteor scientist Invoice Cooke of NASA’s Marshall Area Flight Middle in Huntsville, Ala. Observations of meteors have proven that low-density area rocks and mud fritter away larger in Earth’s ambiance than higher-density rocks.

“The previous standard knowledge was that the low-density stuff was from comets, and the high-density stuff was from asteroids,” he says. However latest observations present that a few of the low-density rocks come from the orbits of asteroids. “So it is extremely believable that low-density stuff from Bennu … would ablate larger within the ambiance and never have an opportunity to create meteorites in any respect.”

If Bennu represents a lacking piece in our understanding of the photo voltaic system’s historical past, finding out that materials in labs on Earth “will assist us fill in a further piece of the jigsaw,” Rozitis says.

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