NASA has successfully landed a probe on the so-called "doomsday asteroid" that could strike Earth with the power of 23 hydrogen bombs.
The OSIRIS-Rex probe was launched in 2016 by NASA, and after several years of manoeuvring, including a slingshot move around the Earth, it finally arrived at Bennu on Tuesday.
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"Achievement unlocked: 'We have arrived!' Our @OSIRISREx mission reached asteroid Bennu," NASA wrote on Twitter.
They're now preparing to study its secrets - spending almost a year taking measurements, before getting in close and collecting samples. The probe will return to Earth in the year 2023.
At the same time, they're working on a plan to launch nuclear weapon-armed spacecraft to protect us if it becomes a threat to humanity.
What is Bennu?
Bennu is about 492m across, and orbits the Sun in the same region as Earth and Mars. An ancient asteroid, it has traces of the materials that built the sun and early planets.
NASA scientists want to know more about the beginnings of our universe and the origin of life. Chief scientist James Green says the samples they collect could unlock the secrets of our planet's beginnings.
"This mission is all about finding how materials, objects like this, fit in with the origin of the Earth and potentially how it may have started life here on Earth," he says.
"Missions like this will bring in an enormous amount of new information that really is going to tell us about the origin and evolution of life."
Why is Bennu a threat?
Bennu has been called both the "doomsday asteroid" and "apocalyptic asteroid".
Physicists estimate Bennu has a one-in-2700 chance of slamming into the Earth on September 21, 2135.
If Bennu hits Earth, scientists estimate the energy unleashed would be 23 times bigger than the biggest hydrogen bomb ever exploded.
It's not big enough to wipe out life as we know it, but could cause "immense suffering and death", says OSIRIS-REx principal investigator Dante Lauretta.
Millions could die if it hit exactly the right spot, while if it hit the ocean there would be a tsunami like those that hit the Indian Ocean in 2004 or Japan after the Tohuku quake - bad news for those on the coasts.
Fortunately, NASA is working on a plan to fight asteroids like Bennu off.
The US space agency has revealed plans for a new spacecraft called HAMMER, which stands for Hypervelocity Asteroid Mitigation Mission for Emergency Response.
A fleet of HAMMER craft, each weighing 8.8 tonnes, would be directed at any incoming asteroid deemed a threat to humanity.
If the asteroid is big enough, the HAMMERs will be armed with nuclear weapons, BuzzFeed News reported.
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