Yes, asteroid Bennu has a chance of hitting Earth. No, you shouldn’t worry about it. Let’s dive into the facts without the click bait “asteroid could destroy Earth” headlines.

First off, why is Bennu in the news? NASA is gearing up for the third mission of the New Frontiers program. That’s the same program responsible for New Horizons and Juno. A spacecraft, OSIRIS-REx, is scheduled to lift off from Cape Canaveral on September 8th. It’s tasked with meeting the near-Earth asteroid (Bennu) in August 2018.

After two years of intense study, OSIRIS-REx will grab a surface sample before returning back to Earth. If everything goes smoothly, OSIRIS-REx and a piece of Bennu will be back on Earth by 2023.

OSIRIS-REx’s main goal is to help us better understand how asteroids could have seeded life on Earth. The spacecraft will attempt to gather at least 60 grams of Bennu containing organic material. You can read more about how OSIRIS-REx will find the perfect sample of Bennu in my earlier post.

OSIRIS-REx and Bennu

While the main mission will be learning about asteroids part in bringing life to Earth, scientists will also use the close encounter to fine tune the rock’s orbit.

And that brings us to this week. You may have seen several articles talking about how Bennu could destroy Earth. Even ABC News jumped on the “giant asteroid that could destroy Earth,” bandwagon. Although their article did downplay the risks posed by Bennu. If only their title did the same.

Here’s what NASA has to say about Bennu. Officially, it is a potentially dangerous asteroid. Right now, scientists peg its chances at striking Earth at about 1-in-2,700. And that chance won’t happen until the last quarter of the 22nd century according to NASA scientists.

So, even if Bennu does strike Earth – we won’t be around to see it. Unless we start living to 200 all of a sudden (current life expectancy in the U.S. was just under 79 years in 2012. Technology has some work to do).

Also, the 1-in-2,700 chance is related to an Earth flyby around 2135. If Bennu enters a ‘keyhole’ between Earth and the moon, its orbit will shift enough to make a later impact with Earth likely. At least, humanity will know it’s on the way.

Let’s say Bennu hits the ‘keyhole’ and impacts Earth in the last quarter of the 22nd century – what happens? There’s some good news and bad news. First, the good. It won’t destroy Earth. Bennu’s diameter is 1,614 feet. Big, but not wipe everything out big.

The bad news? You don’t want to be where it hits. The destruction would be devastating, but it wouldn’t be global.

Scientists believe an asteroid needs to be about 3,280 feet in diameter to cause a global disaster. The one that helped off the dinosaurs? That asteroid was believed to be about 6 miles across.

Time is on our side. We don’t have the technology today (that we publicly know about) to prevent a collision. But in 2175? I’m sure humanity can come up with something. And hey, if OSIRIS-REx can land in 2018 – we could always turn to Michael Bay in 100 years.

The Yarkovsky effect

OSIRIS-REx will help fine tune orbital measurements of Bennu by observing the Yarkovsky effect. As sunlight hits its dark surface, the asteroid absorbs it and later radiates it away as heat. This effect creates incredibly small changes in its orbit. But the changes are enough for the asteroid to possibly hit Earth one day.

“We’ll get accurate measurements of the Yarkovsky effect on Bennu by precisely tracking OSIRIS-REx as it orbits the asteroid,” Edward Beshore (Deputy Principal Investigator for the mission) said in 2014. “In addition, the instrument suite the spacecraft is carrying is perfectly suited to measure all the things that contribute to the Yarkovsky effect, such as composition, energy transport through the surface, temperature, and Bennu’s topography. If astronomers someday identify an asteroid that presents a significant impact hazard to Earth, the first step will be to gather more information about that asteroid. Fortunately, the OSIRIS-REx mission will have given us the experience and tools needed to do the job.”

Bottom line? Bennu may hit Earth in about 150 years or so. Or, it might not. OSIRIS-REx will tell us more over the next few years. And Bennu won’t be the end of the world even if it does head our way.

Top image: Concept of impact that created Bennu.

Image credits: NASA


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