The results of one of the most important experiments carried out to date in space have just been published in the journal Nature: NASA’s DART mission successfully diverted an asteroid 160 meters in diameter called Dimorphssatellite of a 760 meter asteroid cataloged as didymus. That DART impact with Dimorphos occurred on September 27, 2022 at 0:14am CET and marked a pivotal moment.
The suggestions are of such a magnitude that they open a new era of active planetary defense. We have a defense plan thanks to multiple study missions of these bodies, which in recent decades have increased our understanding of the near-Earth asteroids, grouped into various groups according to their orbits. And, almost unintentionally, this field exemplifies that the investment made in the last decades in space provides scientific milestones that mark the future.
The possibility of an impact of an asteroid with the Earth is not zero
The possibility of an impact with an asteroid of a few hundred meters is low, but not null, although it seems relegated to science fiction novels and movies. This latent danger, like many others linked to our own runaway use of planet earth’s resourcesthreatens our existence.
The scientific community led by NASA and Johns Hopkins University has decided to take action on the matter and use the growing knowledge about asteroids to test the efficiency of the method of kinetic impact against an asteroid. This technique seeks to transfer the kinetic momentum of a kamikaze probe to the asteroid, without using an explosive charge.
we could think a priori which is a mere applied physics experiment, similar to the one we perform on a pool table. Nothing could be further from the truth.
DART reached Dimorphos at a speed of 6.14 km/s. When we hit an asteroid at hypervelocity, a part of the collision is transmitted elastically but, as a crater is excavated, an additional momentum is created caused by the emission of materials in the opposite direction of the projectile. This «recoil» component participates in the momentum supplied to the asteroid and contributes very efficiently to diverting it from its trajectory. In fact, the materials ejected after the impact created multiple filaments of particles that could be followed with telescopes from the ground and even from space.
The milestone achieved by the DART kinetic impactor
The good news of the results that are now coming to light is the great efficiency demonstrated in deflecting the Dimorphos asteroid. In it article led by Andrew F. Chengfrom the Johns Hopkins University Applied Physics Laboratory, we quantified the so-called Beta factor associated with that inelastic component that causes recoil and that plays in favor of increasing the effects of a kinetic impactor.
In fact, the experiment far exceeded expectations as that angular momentum transfer multiplier associated with the inelastic component of deflection reached a value of 3.6. That means that the contribution to the moment of that recoil by the particle ejection far exceeded the incident impulse from DART. This parameter is of vital importance and just the most important to quantify in an asteroid of these characteristics, a pile of rubble as the images revealed.
As a consequence of the diversion, let’s not forget that the objective was to shorten the orbital period of Dimorphos around Didymos by just over a minute, but it was reduced by 33 minutes, as detailed in the article. article led by Cristina A. Thomas of Northern Arizona University. It describes the observations made to quantify that orbital period based on the photometric observations made of the binary system using the largest available telescopes.
is other work, led by Jian-Yang Li from the Planetary Science Institute in Tucson, Arizona, preferred the evolution of filaments populated by particles ejected after excavation from the impact and which evolved over the months withstanding the radiation pressure of sunlight. The results are of great relevance to understand what happens to the materials that are detached after the impact and the time that they remain around them.
Such results encourage planetary defense to be developed efficiently to take action against any asteroid detected in a future direct collision path against our planet. precisely in the article led by Terik DalyAlso from the Johns Hopkins University Applied Physics Laboratory, we describe the magnitude of the scientific milestone that is to hit Dimorphos with a robotic and autonomous probe like DART, as well as describe in detail the discoveries made about the nature of Dimorphos and the impact site.
Even so, the key to our ability to deflect asteroids will continue to invest in the early detection of all those bodies that pose a real danger. Although it is not an easy task, thanks to the revolution in CCD digital camera technology, we can discover hundreds every year and, no less important, follow and pinpoint the movements of those already known.
31,361 known asteroids and 119 comets in near-Earth space
At present, the monitoring programs, initially encouraged by NASA, It shows that there are about 31,361 asteroids and 119 comets in near-Earth space. and that, at some point, one could be identified in a probable future collision path with Earth. In fact, this has already happened six times, but with the salvation that fall happened with asteroids of a few meters in diameter that hit our planet more often and generate meteorites.
We currently know of more than 10,400 potentially dangerous asteroids as large or larger than Dimorphs, and we must add a significant percentage of small asteroids that remain undiscovered.
The main threats we face are smaller asteroids, around 150 meters, of which we still don’t know about 60%, and also certain extinct comets such as 2015 TB145a rocky object 650 meters in diameter known as the “Halloween asteroid”.
That skull-shaped object put us on alert when it was discovered just three weeks before its passage on October 31, 2015 at a little more than the distance of the Moon, due to being very reflective and following a very eccentric, extended orbit. practically to the orbit of Jupiter. Such objects, being able to strike our planet with much higher energy than a conventional asteroid, exemplify the diversity and complexity of the problem we face.
It is not possible to be catastrophic since all the effort to discover and catalog these bodies allows a better quantification of the frequency of impact and suggests that an event such as that of Tunguska would occur every several centuries. It also suggests that, fortunately, impacts by kilometer-sized asteroids occur every several tens of millions of years. In any case, the catalog of the Sentry Program of the Center for the Study of Small Objects (CNEOS) of the Jet Propulsion Laboratory (JPL) ensures that, among the cataloged near-Earth asteroids, none is a source of risk on a scale of several centuries. Thus, those catastrophic news to which we are sadly becoming accustomed to each close encounter with the Earth of an asteroid are totally unfounded.
The enriching role of a past marked by impacts
In the remote past, the Earth was born after innumerable impacts with asteroids and even, in a final phase, they were with authentic planetary embryos, the dimensions of the planet Mars itself. If we talk on a larger time scale of thousands of millions of years, scientific evidence shows that The impacts of asteroids and comets have played a key role in the history of the Earth, particularly in the transport of water and the evolution of life itself..
Currently, the flow of interplanetary matter is not negligible: each year about 100,000 tons reach Earth and, although most of it does not reach the Earth’s surface, it does evaporate and become part of our atmosphere.
Perhaps due to the challenge of correctly interpreting cataclysms caused from outer space, a large part of the population continues to underestimate this danger that hangs over humanity. Despite this, awareness of the Tunguska impact on June 30, 1908 and its association with an asteroid that, despite being less than 50 meters in diameter, devastated 2,200 km² of Siberian taiga, should not make us reconsider.
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In this context and with the healthy desire to continue learning, DART shows us the way: space exploration and a determined approach to the problems facing humanity, using our scientific-technological capabilities, will be the key to our survival. .
This article was originally published on The conversation. read the original.