You might have seen news stories about an asteroid called 1950 DA that supposedly has a one in 300 chance of impacting the Earth in 2880. They are all kinds of wrong, and here's why.]
Originating at the Telegraph and replicated by various other news outlets last week, the story that asteroid 1950 DA is set to wipe out life on Earth in 2880 was inspired by recent research that examined how rapidly this asteroid rotates.
Conducted by researchers at the University of Tennessee in the US, the results of the study did little to suggest that the well-known asteroid's chances of hitting the Earth had in any way increased, but the team did find something rather remarkable about the way it's been spinning as it makes its way around its orbital path. According to Phil Plait at Slate:
"The asteroid spins so quickly that it should fly apart! You might think of asteroids as solid, monolithic chunks of rock, but we know that some are “rubble piles”, collections of smaller rocks held together presumably by their own gravity. They probably started out solid, but repeated collisions over the eons have riddled them with cracks, so they are more like gigantic bags of shattered rock.”
Discovered in 1950, Asteroid 1950 DA is a rubble pile, and it’s rotating so quickly that a ‘day' on this asteroid lasts about two Earth hours. An object that’s spinning so fast - especially an object that’s made up of a bunch of smaller objects - should fly apart, but for some reason 1950 DA remains intact, and scientists aren’t entirely sure why.
This new research, published in Nature, seeks to explain the phenomenon, suggesting that a concept known as the van der Waals force could be in play. The van der Waals force describes the effects of an electrostatic charge that occurs between molecules, and it's often used to explain how geckos stick themselves so effortlessly to walls and ceilings. Where asteroid 1950 DA is concerned, the tiny force of momentum that's created by the infrared photons it emits when it’s warm could, over many years, affect how it rotates, and where its orbital path leads.
Which ties into what makes 1950 DA interesting to news outlets who love a good asteroid scare. In 2002, asteroid 1950 DA had the highest 'Palermo rating’ - a scale used by astronomers to rate an object’s chance of impact - of all known near-Earth objects, and since then it’s become somewhat of a poster-child for alarmist space news. Near-Earth objects, or NEOs, are registered as such if their orbits take them within a relatively close distance to Earth, and by “relatively”, we mean on the cosmic scale.
To put this in perspective: "Looking over the next few decades, a typical pass [for 1950 DA] is tens of millions of kilometres away, with some as close as five million kilometres - which is still more than 10 times farther away than the Moon!” says Plait at Slate. "Still, that’s in our neighbourhood, which is one of the reasons this asteroid is studied so well. It gets close enough that we can get a decent look at it when it passes.”
But could it impact the Earth? Plait says yes, but some force would need to alter its orbital path in order for this to happen, and that’s an extremely difficult, if not impossible, thing to predict. But as Plait points out, we do have measurements of its orbital behaviour stretching back to 1950, which means we have a better idea of the asteroid’s future movements than we do for any other known asteroid.
Last year, scientists mapped out their predictions for 1950 DA based on these measurements, and after accounting for all the small effects that could change its orbital path over many years, they’ve come up with their figure. "They found that the probability of an impact in 2880 is about 2.48 x 10-4, which is about 1 in 4000," says Plait. "That’s really small."
Looks like we're probably going to be okay after all.
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