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♪♪♪

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In 2135, a potentially hazardous asteroid called Bennu

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will make a close flyby of Earth.

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During this encounter, our planet’s gravity will tweak Bennu’s path,

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making it a challenge to calculate its future trajectory

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and the odds of a potential impact late in the 22nd century.

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Why is this hard to determine?

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Well, we know how gravity works…

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but there are still uncertainties in Bennu’s trajectory

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that will be magnified by the close encounter.

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In addition to gravity, asteroids can be pushed around

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by non-gravitational forces like the Yarkovsky effect.

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When sunlight strikes a rotating asteroid, the dayside heats up.

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As the asteroid turns, the night side cools down

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and releases the heat.

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This exerts a small thrust on the asteroid,

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which can change its direction over time.

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The Yarkovsky effect is challenging to model, but it can make

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a big difference in determining where asteroids end up.

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Because we don’t know exactly how the Yarkovsky effect

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will perturb Bennu’s orbit, we have limited knowledge

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of where Bennu will be as it approaches Earth in 2135.

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Scientists thus have to consider a range of possible trajectories,

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depending on how strongly the Yarkovsky effect is pushing on Bennu.

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A few of these trajectories line up with regions of space

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called gravitational keyholes.

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If Bennu were to pass through a keyhole,

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Earth’s gravity would bend its path in just the right way

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to cause an impact on a subsequent orbit,

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late in the 22nd century.

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The odds of this actually happening are quite low,

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but scientists want to know as much as possible.

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That’s one reason why NASA sent the OSIRIS-REx spacecraft

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to study Bennu from 2018 to 2021.

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OSIRIS-REx greatly improved our knowledge of Bennu’s

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position, density, thermal inertia, and other properties

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that can influence how its orbit will evolve over time.

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The new data allowed scientists to significantly reduce

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uncertainties in Bennu’s predicted orbit,

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ruling out a number of keyholes for the 2135 flyby,

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and eliminating several future impact scenarios.

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While Bennu remains a hazardous asteroid, we can now make

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better models of its orbital evolution thanks to OSIRIS-REx.

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This will allow us – and our descendants –

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to better calculate Bennu’s risk

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in the decades and centuries to come.

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♪♪♪