“The international systems we’re putting in place to find, track and characterize – and, if it comes to it, mitigate the impacts of – hazardous asteroids and comets are working as intended,” said Andy Rivkin, an astronomer and planetary defence researcher at the Johns Hopkins Applied Physics Laboratory in Maryland.
Here’s what you need to know about 2024 YR4.
How was this asteroid discovered?
It was identified by the Asteroid Terrestrial-impact Last Alert System, or ATLAS, four telescopes around the world that hunt near-Earth objects and are funded by NASA. Its telescope in Chile found 2024 YR4 on December 27, just two days after a close approach to Earth.
It’s now speeding away from the planet and getting fainter by the day.
How big is 2024 YR4?
According to the European Space Agency’s Near-Earth Object Coordination Centre, it is between 130 and 330 feet long. This size range is based on the amount of sunlight it is reflecting. Without knowing exactly how reflective 2024 YR4’s surface is, only a range of sizes can be given.
A more accurate estimate could be made using radar, but that won’t be possible until the asteroid makes another close, but perfectly safe, pass by Earth on December 17, 2028.
Is an asteroid of this size a concern?
Yes.
A 130-foot asteroid is comparable to the Tunguska impactor, a meteor that exploded over a remote patch of Siberia in 1908 and decimated an 800-square-mile forest (that’s over twice the size of New York City). A 330-foot asteroid would cause far greater localised damage: a strike on a city would destroy much of it. If the object survives its journey through the atmosphere and strikes the ocean just offshore, the resulting tsunami could devastate nearby coasts.
How do we know there is a chance of an impact in 2032?
The Centre for Near-Earth Object Studies, at NASA’s Jet Propulsion Laboratory in California, is home to America’s asteroid and comet cartographers. Using sophisticated software, they track the motion of all known near-Earth objects.
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One of their programs, Sentry, assesses the possible orbits of known near-Earth objects and determines whether they stand even a tiny chance of striking Earth within the next century. Those whose impact odds cannot be confidently reduced to (essentially) zero remain on the Sentry Risk List.
“The possibility that 2024 YR4 might impact in 2032 was identified right after discovery,” said Davide Farnocchia, a navigation engineer at the NASA center. But based on just a few observations, the prediction uncertainties for 2032 were initially very large. As the number of observations grew to the hundreds, he said, “the impact probability has gradually increased over the last month and has now surpassed 1 per cent, an important threshold.”
The Torino Scale is a tool for communicating how concerned the public and policymakers should be about an asteroid. It ranges from 0 (the likelihood of a potentially deadly collision is effectively zero) to 10 (a collision is certain and may imperil all of human civilisation).
2024 YR4 currently sits at 3: a close encounter, less than a decade away, meriting attention by astronomers, one that has a chance of 1 per cent or greater of a collision capable of localised destruction.
This is the second-highest rating ever given to an asteroid. Only Apophis, an asteroid once thought to be a threat, briefly reached a 4. But as we learned more about Apophis, we found it had no chance of striking Earth for at least a century.
When can we expect the impact odds to change?
What normally happens is that the impact odds plummet to zero as more observations come in and the asteroid’s orbit is better known with more precision.
The same story will probably unfold with 2024 YR4. “The most likely outcome is that further observations will rule out an impact,” Rankin said.
2024 YR4 is getting extremely faint as it travels away from Earth, meaning most telescopes are going to struggle to track it. “However, given this is a special case, members of the community have requested (and received) time on some of the larger and more capable facilities,” Rivkin said. “Those should do OK through April.”
Astronomers will also have an even greater opportunity to refine their predictions during the December 2028 flyby. But until then, it’s possible that an impact in 2032 won’t be entirely ruled out.
“We expect the impact probability to go to zero rather than 100%,” Rivkin said. “But it may take a few years before we get the data to show that.”
Ultimately, should we be worried about 2024 YR4?
No, not at present. It’s very likely to miss the planet in 2032.
And if we find out that it will hit, “we might be able to do something about it,” Rankin said.
One option, if space agencies had enough time to mount an operation, would be to attempt to alter the asteroid’s path by crashing a spacecraft into it.
If that failed, or wasn’t possible, and governments worked out a precise impact location, they could evacuate people who might be at immediate risk.
This article originally appeared in The New York Times.
Robin George Andrews is the author of How to Kill an Asteroid, a book about the science of planetary defense.
