Although the odds are slim and NASA says it is extremely unlikely Bennu will ever hit Earth, the space agency says there is a one in 2,700 chance of an Earth impact between 2175–2199. Which, considering the implications of such a strike, may still seem like uncomfortable odds. While the 500 metre space rock is not comparable to the 10 kilometre-wide asteroid which put an end to the dinosaurs, Bennu would still have a devastating impact on our planet.
If Bennu, which NASA is currently studying via its OSIRIS-Rex spacecraft which arrived there in the December, were to hit Earth, it would likely strike the planet at 7000 metres per second – a standard speed asteroids hit at thanks to Earth’s gravitational pull. The speed translates to a staggering 25 MILLION kph.
Weighing a staggering 78bn kilograms and travelling at hyperspeeds would create an explosion the likes of which humanity has never seen.
Physicist Allen Bryan, assistant professor at the University of Alabama at Birmingham, US, believes the collision could create an explosion which packs the energy of 1150 megatons of TNT.
For reference, the nuclear bomb the US dropped on Hiroshima during World War 2 packed just 0.015 megatons of TNT – making Bennu’s potential impact more than 76,000 times more powerful.
Clearly then, the impact would be immense.
Prof Bryan wrote on Q+A site Quora: “Were there to be an impact on land, we can extrapolate from nuclear weapons; the direct fireball could be as large as 20 km, with concussion effects for over 200km.”
However, with the surface of the Earth being 70 percent water, the most likely place the asteroid would land is in one of the planet’s oceans, which would cause mega tsunamis and a climate shift.
Prof Bryan continued: “The most likely scenario would be an airburst over an ocean, possibly followed by a tsunami and/or disruption in weather due to vaporised seawater.”
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OSIRIS-Rex has now completely mapped Bennu, and has selected four potential sites which it could select samples from.
The plan next is to whittle these sites down to two, where it will collect samples from a one inch area.
NASA was not prepared for just how rocky Bennu would be, so it is looking for an area where samples are fine enough for the machine to ingest.
Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson, said: “We knew that Bennu would surprise us, so we came prepared for whatever we might find.
“As with any mission of exploration, dealing with the unknown requires flexibility, resources and ingenuity.
“The OSIRIS-REx team has demonstrated these essential traits for overcoming the unexpected throughout the Bennu encounter.”