One day, an asteroid named Bennu could hit Earth, punching a hole in the planet with the force of 22 atomic bombs.
Thankfully, that day is more than 150 years in the future.
But today, a tiny piece of the asteroid will make a much softer landing in the Utah desert – after humans punched a hole in Bennu to collect a handful of its surface.
The sample was collected by Nasa’s OSIRIS-REx spacecraft – full name Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer – on October 20, 2020 in a surprisingly explosive landing.
Based on two years’ observation of the asteroid by OSIRIS-REx, and the results of a Japanese mission collecting a fragment from asteroid Itokawa, the Nasa team expected the surface to be relatively solid and stable.
However, despite OSIRIS-REx descending at just 10cm per second, it blasted a huge hole in the surface, scattering tonnes of rocks and debris and leaving an eight-metre wide crater. Meanwhile, its thrusters stirred up the particles, clogging up its instruments.
Fortunately, the whole operation lasted only 30 seconds, and the craft was able to float away unscathed.
The manoeuvre and previous test runs provided scientists with a surprising insight into the asteroid, which Nasa says has ‘consistently defied scientists’ expectations’. The surface, instead being relatively solid with a light top layer of dust and debris, behaved more like a fluid.
An almost complete lack of cohesion, one of the ways particles are held together, meant the surface behaved like a ball pit – with rocks, dust and debris loosely stacked on top of each other but easily moved by a solid object.
The sample collection, known as a touch-and-go – or tag – event, was the highlight of a seven-year-mission to learn more about the asteroid, that on Tuesday, September 24, 2182, has a 1 in 2,700 chance of colliding with Earth.
The odds of it hitting sometime between now and 2300 are even lower at about 1 in 1,750.
In 2135 the asteroid will make a close approach, which scientists who haven’t yet been born will use to understand Bennu’s exact trajectory and how Earth’s gravity will alter the asteroid’s path – affecting the chances of hitting the planet on another orbit.
For now however, Bennu is set to provide more wonder than worry, as the key to unravelling more of its mysteries parachutes back to Earth today, landing at around 3.55pm UK time.
Live coverage of the event will be broadcast on Nasa’s YouTube channel.
The space agency caused great excitement in July when a team was spotted collecting a ‘flying saucer-shaped’ object from the Utah desert, but rather than a UFO, it proved to be a rehearsal for recovering the OSIRIS-REx return capsule when it touches down.
From its landing point in the Department of Defense’s Utah Test and Training Range, 70 miles west of Salt Lake City, the capsule and its samples will be whisked away to Nasa’s Johnson Space Center in Houston. Special tools have been developed for the analysis, including those to look at material smaller than a grain of sand.
The team hopes Bennu will provide insight into the role of asteroids in the formation of the early solar system – it is predicted to be 4.5 billion years old, essentially serving as a time capsule full of cosmic secrets.
Nasa will take two years to complete its analysis of the asteroid – which still leaves 157 years before a potential collision.
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