Artist’s conception of Hera Mission
The last week of the year always seems to bring out the worst sort of doomsday predictions. But after a pre-holiday interview with one of France’s leading experts on near-Earth asteroid planetary defense, there’s reason for cautious optimism.
For the next 100 million years, we don’t have to worry about a civilization-ending near-Earth impactor, Patrick Michel, a planetary astrophysicist at France’s CNRS national research institute, told me in his office at Nice Observatory.
Asteroids that could threaten Earth are all 140 meters or less; none are civilization killers, says Michel. But the impact frequency of objects in that size range occur every 10,000 years on average. So, the likelihood that in our lifetime, an object of that size would hit earth remains extremely small; it’s not zero, but it’s small, says Michel.
Depending on the density and the speed of the asteroid, if a 140-meter asteroid impactor hit off the coast of Nice, France, it would likely wipe out the whole French Riviera, says Michel. That’s why we need to have a robust plan, he says.
We’re Making Strides
In 2022, NASA’s Double Asteroid Redirection Test mission successfully with the asteroid moonlet Dimorphos, an object just 530 ft. in diameter, says NASA. Dimorphos, in turn, orbits a larger 2,560 ft. asteroid named Didymos.
Although DART exceeded expectations, the European Space Agency is launching, Hera, a follow-on mission to Didymos and Dimorphos in October of 2024. It will rendezvous with the binary asteroid in early 2027.
We need to measure the mass of Dimorphos to measure the efficiency of the DART impact to make sure the deflection test can be extrapolated to other scenarios, says Michel, Hera’s principal investigator. From DART, we learned that before the impact, the time it takes the small moon to make one turn around the central body was 11 hours and 55 minutes, says Michel. After the DART impact, that orbit was decreased by 33 minutes. DART made a deflection that reduced the orbital period, he says.
How Far Are We From Having A Scalable Deflection Mechanism?
The more we do the deflection in advance, the less energy we would need to deflect the asteroid, says Michel. At this stage, however, to use a DART type mitigation strategy, we would need a minimum of a decade of advance impact warning, he says.
But Michel says there is still a communication disconnect between politicians, the media and planetary defense scientists.
This was a recurring theme in the 2021 disaster film, “Don’t Look Up.”
Although in the film, Earth was in danger from a long period comet instead of an asteroid, Michel says that the way the film depicts the interaction of scientists with the media and politicians is accurate.
To be seen as credible is very difficult; you usually have only two minutes to explain the complex problem between two news segments which have nothing to do with the topic, says Michel. The problem is to make the politicians believe you because they don’t have any science knowledge, he says.
At least at NASA, there is a planetary defense coordination office, says Michel. But in many countries, like France, for instance, he says planetary defense is not a big subject.
Michel says that in the event of either a “Don’t Look Up”-type high inclination comet or a 140-meter asteroid headed on an unexpected trajectory towards Earth with only two years of advance warning or less, the only option would be nuclear. A DART type mitigation strategy simply would not work, he says.
To that end, in a paper published just last week in The Planetary Defense Journal, researchers at the Lawrence Livermore National Lab in California have newly assessed the potential for using a nuclear device to defend earth from catastrophic asteroid impacts.
If there’s enough warning, we’d then have two options, says LLNL. The first option would be to detonate the device and deflect the asteroid, which would keep it intact, but would push it on a trajectory that would not impact Earth. The second option would be to completely disrupt the asteroid into small, fast-moving fragments that would also miss our planet, says LLNL.
But Michel reasons that if we use such a strategy to destroy a potential near-Earth impactor, we’d have a lot of fragments coming straight for us.
Even more reason to hone our mitigation strategies.
Asteroids are super complex and super diverse, says Michel. We need to keep doing these missions in order to practice so that when we try to interact with them we are efficient in doing so, he says.
