Space

NASA's asteroid sampler narrowly avoided sinking into surface of Bennu

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Artist's concept of OSIRIS-REx
NASA
Bennu as seen from NASA’s OSIRIS-REx spacecraft
NASA's Goddard Space Flight Center/University of Arizona
OSIRIS-REx spacecraft touches down on Bennu in October 2020
NASA Goddard Space Flight Center
Artist's concept of OSIRIS-REx
NASA
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In October 2020, NASA’s OSIRIS-REx spacecraft made history by touching down on the asteroid Bennu and grabbing a sample of rock and debris. New analysis of this encounter has revealed the probe was lucky to avoid sinking into the asteroid's surface, which mission scientists have found to be so loosely packed it resembles a pit of plastic balls.

This new perspective on the surface composition of Bennu comes via closeup images OSIRIS-REx collected as it snatched its precious sample. Prior laboratory testing had indicated the probe would barely make a divot in the asteroid throughout this process, but the images revealed pebbles had spread all around and that a massive crater measuring 26 feet (8 m) across had been created.

So, in April 2021, the scientists sent the spacecraft back for another inspection of the mess. This enabled them to analyze before and after images of the sampling site, and assess acceleration data the probe collected as it touched down. This revealed a very tiny amount of resistance from the surface, which the team compared to pressing down the plunger on a French Press coffee maker.

OSIRIS-REx spacecraft touches down on Bennu in October 2020
NASA Goddard Space Flight Center

The team then ran computer simulations designed to calculate the density and cohesion of Bennu’s surface materials. These were based on spacecraft images and the acceleration data, with the team experimenting with various properties until the simulation married up with the mission data.

This revealed the particles making up the exterior of Bennu were so loosely packed that stepping onto the asteroid’s surface would be like stepping into a pit of plastic balls. So much so, the spacecraft would have sunk into the asteroid if it had’t immediately fired its thrusters to move away from the surface.

“By the time we fired our thrusters to leave the surface we were still plunging into the asteroid,” said Ron Ballouz, an OSIRIS-REx scientist based at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.

The findings present another twist in our perspective of Bennu’s surface, which earlier mission data had revealed to be much more rugged and eruptive than Earth-based observations had suggested. The discovery also has implications for our understanding of other asteroids, and the dangers they may pose to our home planet.

“It’s possible that asteroids like Bennu – barely held together by gravity or electrostatic force – could break apart in Earth’s atmosphere and thus pose a different type of hazard than solid asteroids,” said Patrick Michel,” an OSIRIS-REx mission scientist. “I think we’re still at the beginning of understanding what these bodies are, because they behave in very counterintuitive ways.”

The video below provides an overview of the discovery, while the research was published across two papers in Science and Science Advances.

Source: NASA

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2 comments
paul314
Apparently simulations of collisions with asteroids that break up show many of the same cataclysmic effects as the ones that hit. You don't get the big single crater, but all the energy gets dumped into the atmosphere, flash-broiling and possibly vaporizing a large chunk of the Earth's surface beneath the impact point.
Karmudjun
Not so apparently, but actually - given the Tunguska event of 1908 where an asteroid absolutely vaporized in the atmosphere affecting the surface of the planet. No single impact crater, no vaporized surface of the earth, but trees burned and flattened (or flattened from the shock wave and then burnt from the blast wave) in very remote areas so that scientific study wasn't conducted immediately. Bennu would not yield anything similar unless the trajectory was straight in, center of mass to center of mass. Still, with the Tunguska event, the glancing blow yielded a huge shock wave, and that was theorized to be one solid meteor.