We’re all looking at an asteroid named Bennu. Bennu is believed to be from the asteroid belt between Mars and Jupiter, but has diverted its course due to sunlight, gravitational pull, and its own expulsions. Bennu is pretty cool, with NASA collecting a sample from the asteroid and bringing it back to Earth. On Monday, May 10, at 4:23 p.m. EDT the spacecraft OSIRIS-REx fired its main engines full throttle for seven minutes – its most significant maneuver since it arrived at Bennu in 2018. This burn thrust the spacecraft away from the asteroid at 600 miles per hour (nearly 1,000 kilometers per hour), setting it on a 2.5-year cruise towards Earth. OSIRIS-REx will return in 2023 with that sample. Bennu is believed to have formed 4.5 billion years ago. It has bits of another asteroid on its rocky surface from a previous collision and it shoots out rocks and gas every so often.
Between 2175 and 2199, Bennu will come within 7.5 million kilometers of Earth’s orbit and will be classified as potentially hazardous. Why do we care about something that might be hazardous over 100 years in the future that has a 1 in 2700 chance of hitting? The 1,600 foot (487 meters), 74 billion pound (33.5 billion kilograms) space rock would produce a 1.15 gigaton explosion if it struck Earth. That’s about 23 times larger than the most powerful hydrogen bomb ever detonated, and it’s far from the biggest asteroid out there. PLUS, it takes between 10 (China) and 25 (USA) years to prepare for a possible collision. Not to mention lots of money to build a fleet of each rocket.
No blaring alarms, no screaming people in the streets, no big red button to press to launch an intercepting rocket.
But that’s the idea. Send nuclear rockets up there and divert its course safely away from Earth.
China wants to send 23 Long March rockets to hit the asteroid at the same time. Why not one rocket like in the sci-fi films? It takes a huge amount of energy to turn a rock as tall as the Empire State building. A single nuclear blast would explode it, causing pieces to possibly hit Earth. Multiple rockets would turn it, using extra fuel as both weight and thrust.
The US has a similar idea. It has built HAMMER, which stands for Hypervelocity Asteroid Mitigation Mission for Emergency Response. HAMMER has two modes. In its preferred mode of operation, it would act as an impactor that collides with the asteroid to gently nudge it off course. If there’s not enough time for that, HAMMER’s other option is to detonate a nuclear weapon in order to destroy or deflect the object. The analysis says current US nuclear weapons are sufficiently powerful to knock an object like Bennu off course. Overall efficacy won’t be clear until we get a closer look at Bennu’s makeup. OSIRIS-REx will deliver a sample to Earth in 2023.
Wait, didn’t you just say that using a nuclear blast could blow chunks at Earth? Yes. Which is why we need math and lots of it. If we can calculate with enough years in advance the trajectory of Bennu, the possible trajectory of turning it, and the time it will take for a fleet of rockets to do it (3 years China, 2 years US by current models) , we can build, prepare, and safely avoid any danger.