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Artist's impression of an asteroid – PA
- An asteroid grazed the Earth Thursday being spotted only 24 hours ago.
- The big rock still had the ability to shave a city if it had fallen on our planet.
- A new case proving the difficulty of spotting these dangerous space objects, as Olivier Sanguy, scientific mediator of the Cité de l'Espace in Toulouse, interviewed by "20 Minutes" explains.
The asteroid "2019 OK" has
grazed the Earth Thursday, passing between our planet and the Moon. From a size between 50 and 130 meters, he could have razed an entire city if he had fallen on it, deploying thirty times the energy of the bomb.
Hiroshima.
But this big rock was spotted only 24 hours before we touched, about 77,000 kilometers from our blue planet. This inability to see him earlier questions our surveillance of the most dangerous asteroids. A task more difficult than we think, as Olivier Sanguy explains, scientific mediator
of the Cité de l'Espace in Toulouse, contacted by 20 minutes.
It is customary to think that with all the technological advances, asteroids are easy to spot. How is this a problem?
They are not simple objects to observe, whatever you may think. Like all objects in the solar system, out of the sun, they do not emit light, and reflect very little because they are mainly dark matter. The smaller the body, the farther it is, and the harder it is to see it. It is thought that the vast majority of the most dangerous asteroids, those measuring more than one kilometer, have been cataloged and which would cause – in case of impact – a global planetary catastrophe for humanity. Intermediate asteroids, large enough to survive entering the atmosphere but measuring less than one kilometer, are more difficult to see and less referenced. This was notably the case of "2019 OK", which measured between 50 and 130 meters.
There is also a strong budget limit. Thanks to several automated telescopes, which photograph the same point of space at different times, it is easier to spot asteroids. A point that moves between two photos is enough. But it is expensive and it is not the current priority. Finally, third limit, there are blind spots, including an asteroid arriving by the sun.
The most dangerous asteroids for the Earth have therefore been referenced, but there is a risk with asteroids of intermediate size?
Precisely, and there is little by little an awareness of the dangers that these asteroids represent, says of regional disaster. However, we understand that depending on where the impact takes place, the regional disaster can become a global disaster. For example, "2019 OK", which is called "City Killer", can have major geopolitical consequences if it falls on a major capital like Beijing or Washington. Or in the Middle East, disrupting the global oil cycle.
While we thought we had done the basics by cataloging the asteroids of more than one kilometer, we realize that the asteroids of "regional disaster" can only have the name.
Will this awareness have an impact?
There is an annual campaign where astronomers try to reference asteroids. But awareness is hard to pass when it comes to budget funding. It should not be misunderstood, if the disaster can have an impact on the whole of humanity, it has a low risk of arriving. Also, there is advanced research on asteroid deflection. It's not science fiction anymore,
NASA in particular is testing a program to achieve this kind of technological feat. And it's more glorious than referencing them, it attracts more. But what we try to make clear is that it is useless to know how to divert them if we do not know how to spot them in time. For example, if "2019 OK" was going to impact the earth, no matter what our deflection technology was, it was spotted much too late to do anything.
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Of course, the detail “diagnostic” (detection of NEOs, determination their orbits and other parameters) is the first step to saving Earth. But as for the next step – real and adequate “cure”…
Actually, most of proposed approaches to planetary defense are neither effective nor scalable even to asteroids capable of country-wide destruction. For example, it is unlikely that the kinetic impact will work because of the internal structure of near-Earth asteroids is crumbly: “We think they’re very loose aggregates. They’re not solid through and through” said Melissa Morris, OSIRIS-REx deputy program scientist at NASA Headquarters in Washington, D.C. The detailed photos and probe impacting of Bennu and Ryugu reveal rubble-pile natural properties of the NEOs, which will prevent shock wave propagation and proper impulse transfer.
The nuclear blast method is risky and can pose danger both on the ground and in the atmosphere. This type of explosion could potentially create a stream containing hundreds of “city-killing” radioactive pieces, e.g., in the case of disintegrating a sub-km asteroid. Moreover, as follows from computer simulations, shortly after explosion all of the pieces will tend to settle towards the center of mass, which would still be headed on a collision with the Earth.
The asteroid laser ablation method is not viable because of cooling concerns for powerful (over 100 W) lasers. In space, the laser source will not have a means to radiate heat quickly enough to avoid damage to itself.
As of now, it appears that asteroid ablation using highly concentrated sunlight is the only method that meets all of the following criteria: scalability up to global-threat sizes and any type of hazardous bodies owing to maximum thrusting power without huge volume of propellant, as well as low cost and environmental friendliness. This method creates thrust similar to the laser ablation method, creating a natural rocket out of the asteroid, without the power and heating concerns.
An improved concept for such solar-based deflection using an innovative solar collector was proposed and substantiated in 2013 – see https://link.springer.com/article/10.1007%2Fs11038-012-9410-2
and also a short demo-video