These are not good times for poetry, or at least they don’t seem that way to me. If we don’t care about seeing grandparents die in residences, if we care little that boys and girls learn about the world, past, present and future, and about how to treat each other, if we live in a society where everything must be immediate and it does not fit in our heads to take time to reflect on solutions to problems and how to achieve them together, how are we going to be aware that we are advanced enough to face existential problems that will blow up in our faces sooner or later? Not even if we have suffered it recently does it seem that we learn…
At least this existential pessimism with which I have started my (express) article is not shared by a few scientists and engineers, true Justice League-style planetary defenders, whose dreams and ideas have been supported, thank heavens, for public funds, and that they have embarked on an adventure that has as its objective nothing less than saving our planet (well, more than the planet itself, our existence on it). It could be said that these people, or astrophysicists like me, are catastrophists, fans of more or less realistic Hollywood movies (such as Armageddon either Don’t look up, let each one choose which one is closest to reality), when we warn that perhaps in 200 years, perhaps in 1,000 or perhaps in 10,000, but almost 100% sure, the planet is going to face a cosmic cataclysm. Simply, the Solar System works like this, the Earth was formed by collisions of objects that at first were no more than a few meters in size and that, in a few million years, which for our life is a lot, but for stellar times it is a trifle, they formed something as big as our planetary home or as Jupiter or the Sun itself. And the original bricks are still dancing around, in a slow dance for our times, but unstoppable, there is no one to annul gravity.
Well, that is what they have dedicated themselves to at NASA to create the DART mission, which has met its main milestone —but not its main objective— with great success, a milestone typical of the worst rally driver: crashing your machine against a rock. But now it remains to be seen what we can learn from this cosmic crash.
In addition to crashing a million-dollar probe, the team behind the DART mission has spent more than darts playing pool, or rather, understanding the rules of pool. I am not referring to putting the solid balls in the pocket and ending with the black one, those rules are too human and changeable, I am referring to the immovable and fundamental rules of billiards, which are those of the universe, the physical laws of collisions or clashes between objects.
By collision, the RAE understands “a scratch or wound caused as a result of fighting and rubbing one thing with another”, and by shock it understands “violent encounter of one thing with another”. The second word and definition is the one that makes the most scientific sense, because collisions in physics don’t even have to imply that the colliding elements touch. But it is not our case, DART has touched Dimorfo, it has given him a good touch. But has that touch been like two billiard balls or not? Here is the key question.
We can already imagine that no, no man-made racing car collides with something and remains (almost) impassive as a billiard ball. The question is how close to the game of billiards has DART clashed with Dimorfo. If the collision between DART and Dimorph were very similar to the collision between two billiard balls, and if the approach and impact on the asteroid were optimal, at maximum speed and in the perfect place for our wishes, all the (kinetic) energy of DART would be transferred to Dimorpho. It is what is called an elastic collision in physics, where kinetic energy is conserved, all the energy that objects have before the collision because they move in a certain way is transformed into energy of a different movement of each agent involved in the collision . As the asteroid is much larger than DART, just like if we try to move a truck with our hands, the effect is not going to be very great, but however small, after millions and millions of kilometers and kilometers of travel, perhaps the disturbance suffered is sufficient to save us. I am not referring to this case, Dimorfo is not in the impact trajectory, I am referring to the meteorite or comet that will arrive to endanger life on Earth.
The problem is that collisions in the universe are usually not elastic, but inelastic. Some of DART’s kinetic energy has been transferred to Dimorph in the form of heat, deformation of its surface or even broke it. Part of that initial kinetic energy not converted into final kinetic energy can be lost, but even in the case of an inelastic collision everything is not negative, that is, all the effects that an inelastic collision causes are not wasted and cease to serve to move the object. asteroid from its orbit, which is what we want. Just as in billiards it is sometimes convenient not to hit the white ball very hard to put the colored ball in the hole and make the future easier for us, in the case of a mission like DART the impact speed should not be very high. Because it could cause the asteroid to break apart and expel material on the opposite side of the collision, which would decrease the acceleration that we want to give it to get it out of its orbit. DART’s speed can’t be too low either, because it might not be enough to disturb its movement and prevent it from going where it doesn’t have to go in the future. So neither too bald nor too bald. But to save the planet that phrase has to be converted into numbers, and there has been the work of many years, which will now continue with the real study of the effects of the impact.
And what does it depend on whether the collision is elastic or inelastic and what should the impact velocity be? Well, of many factors, among which we can name, imagining what would matter on a pool table. The composition, density and total mass of the asteroid (playing with wooden balls is not the same as playing with ivory or resin), its shape (try playing with non-spherical balls, like the asteroid!), the point of impact and the angle of incidence (the funniest thing about billiards, playing with the effects), the speed of impact that we have talked about, the characteristics of the surface where the DART actually hit, which could be porous and cushion the shock, or could have hit in a metal vein that makes the collision more elastic, or be basically ice if it were a comet (which would surely be much more difficult to stop with a mission like DART), and a long etcetera. And another very important parameter is the amount of material that is going to be removed from Dimorfo, where it is going to be removed from, and what is going to happen to that material.
Despite how spectacular it has been to live live the clash of DART against Dimorfo, the truly amazing and the most transcendent for the future of our species begins now. We have to make measurements that tell us how the impact was and what effects it had, and for this we also have to analyze all the properties of the asteroid well. To a certain extent, this intellectual and scientific challenge that follows the technical challenge of the DART crash against Dimorpho helps me to overcome the pessimism with which this article began. There is nothing like thinking about how to solve a problem, especially if the company is not easy, but the survival of our genes depends on it.
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