They just saw the light in a magazine Nature the results of one of the most important experiments done to date in space: darts mission NASA successfully deflected a 160-meter diameter asteroid called Dimorphssatellite of another 760 meters cataloged as Didymos. The collision occurred on September 27, 2022 at 0:14 CET and was a key moment.
The consequences are so great that they open a new era of active planetary defense. This is thanks to the numerous missions to study these bodies, which in recent decades have expanded our understanding of near-Earth asteroids, grouped into different groups according to their orbits. And almost unintentionally, this field shows that the investments made in space in recent decades provide scientific milestones that mark our future.
The probability of an asteroid colliding with the Earth is not zero
The chance of hitting an asteroid a few hundred meters away is low, but not zero, although it seems to be the case in science fiction novels and movies. This hidden danger, like many others associated with our unbridled use of the resources of planet Earth, threatens our existence.
The scientific community, led by NASA and Johns Hopkins University, decided to put the matter to the table and use the growing knowledge about asteroids to test the effectiveness of a kinetic impact method on one of these bodies.
This method aims to transfer the kinetic momentum of a kamikaze probe to an asteroid without the use of an explosive charge. we might think a priori which is a simple applied physics experiment like the one we do on the pool table. Nothing is further from the truth.
DART reached Dimorphos at 6.14 km/s. When we collide with an asteroid at hypervelocity, some of the impact is elastically transferred, but as the crater is excavated, additional momentum is created, caused by the ejection of materials in the opposite direction of the projectile.
This “recoil” component is involved in the supply of an impulse to the asteroid and very effectively contributes to its deviation from the trajectory. In fact, the materials ejected after the impact gave rise to numerous strands of particles that could be followed with telescopes from the ground and even from space.
Milestone achieved by DART mission kinetic impactor
The good news about the results that are now emerging is the greater efficiency demonstrated by the DART mission in deflecting the asteroid Dimorphos. In a paper led by Andrew F. Cheng of the Johns Hopkins University Applied Physics Laboratory, we quantified the so-called beta factor associated with this inelastic component, which causes recoil and plays to enhance the effects of the kinetic impactor.
In fact, the experiment far exceeded expectations, since the multiplication factor of the transferred angular momentum, associated with the inelastic component of the deflection, reached a value of 3.6.
This means that the contribution to the momentum of this recoil from the ejection of particles is much larger than the incident momentum from the DART mission. This parameter is vital and most important for quantifying an asteroid with debris pile characteristics, as the images show.
As a result of the deflection, the goal was to shorten Dimorphos’ orbital period around Didyma by just over a minute. But it was shortened by 33 minutes, as detailed in an article led by Christina A. Thomas of Northern Arizona University. It describes observations made to quantify this orbital period. This is based on photometric observations of the binary using the largest available telescopes.
Another work led by Jian-Yang Li of the Planetary Science Institute in Tucson, Arizona, studied the evolution of filaments populated by impact excavated particles that developed over months under the pressure of solar radiation. The results are of great importance in understanding what happens to materials released after an impact. And the time they stay by your side.
Such results indicate that planetary defenses can be effectively designed to counter any asteroid moving on a collision course with the Earth. It is in a paper led by Terik Daly, also of the Johns Hopkins University Applied Physics Laboratory, that we describe the magnitude of the scientific milestone of hitting Dimorphos with a robotic and autonomous probe such as DART. Just as the discoveries made about the nature of this asteroid and the place of impact are described in detail.
However, the key to our ability to deflect asteroids will be to continue investing in the early detection of all those bodies that pose a real danger. Although this is not an easy task, thanks to the revolution in digital CCD camera technology, we can discover hundreds of such images every year. And, no less important, to track and refine the movements already known.
31,361 known asteroids and 119 comets in near-Earth space
Currently, monitoring programs initially encouraged by NASA indicate that there are about 31,361 asteroids and 119 comets in near-Earth space. And that at some point it is possible to determine the likely path of a future collision with the Earth. In fact, this has already happened six times, except that it happened with asteroids several meters in diameter, which more often hit our planet and cause meteorites to fall.
We currently know of over 10,400 potentially hazardous asteroids as large or larger than the Dimorphs. We must add a significant percentage of similar bodies, but smaller, which remain undiscovered.
The main threats we face are asteroids around 150 meters in size, about 60% of which are still unknown to us. Also some extinct comets such as 2015 TB145rocky object with a diameter of 650 meters.
This skull-shaped object put us on our guard, as it was discovered only three weeks before its passage on October 31, 2015, at a distance slightly greater than the distance from the Moon. This is because it is highly reflective and follows a very eccentric orbit, practically extended to that of Jupiter. Such objects, capable of colliding with our planet with much more energy than a normal asteroid, illustrate the variety and complexity of the problem we face.
Impossible to be catastrophic, as all efforts to locate and catalog these bodies allow us to better quantify impact frequency and suggest that an event like Tunguska will occur every few centuries. They also suggest that, fortunately, kilometer-long asteroid impacts occur every few tens of millions of years. In any case, the Jet Propulsion Laboratory’s (JPL) Center for Small Object Science (CNEOS) Sentry program catalog ensures that none of the cataloged near-Earth asteroids poses a risk on a multi-century scale. Thus, the catastrophic news that we get used to at each relatively close collision of an asteroid with the Earth is completely untenable.
The enriching role of the past marked by impacts
In the distant past, the Earth was born after countless asteroid impacts and even, in the final phase, they were with genuine planetary embryos, the size of the planet Mars itself. On a larger time scale of billions of years, scientific evidence shows that asteroid and comet impacts have played a key role in Earth’s history. In particular, with the transfer of water and the evolution of life itself.
At present, the flow of interplanetary matter cannot be neglected. Every year, about 100,000 tons reach the Earth, and although most of this amount does not reach the Earth’s surface, it evaporates and becomes part of our atmosphere.
Perhaps due to the difficulty of correctly interpreting the cataclysms caused by outer space, a large part of the population continues to underestimate this danger hanging over humanity. Despite this, the realization of the Tunguska strike in 1908, which, despite the fact that its diameter was less than 50 meters, devastated 2200 km² of the Siberian taiga, should make us reconsider our views.
In this context and with a healthy desire to continue learning, the DART mission leads us the way. Space exploration and a decisive approach to the problems facing humanity. Especially, using our scientific and technical capabilities, which will become the key to our survival.
Source: Hiper Textual
