DART mission: humanity already has a planetary defense plan

They just saw the light in the magazine Nature the results of one of most important experiences in space to date: NASA’s DART mission has successfully hijacked a asteroid 160 meters in diameter called Dimorphos, satellite of a 760 meter asteroid listed as Didymos. This DART impact with Dimorphos happened on September 27, 2022 at 0:14 CET and marked a pivotal moment.

The implications are of such magnitude that they usher in a new era of active planetary defense.. We have a defense plan through multiple missions to survey these bodies, which over the past decades have increased our understanding of near-Earth asteroids, grouped into various groups according to their orbits. And, almost unwittingly, this area illustrates that the investment made over the past decades in space provides scientific milestones that mark our future.

The possibility of an impact with an asteroid a few hundred meters away is low, but not zero, although it seems relegated to science fiction novels and movies. This latent danger, like so many others related to our own unbridled use of planet Earth’s resources, threatens our very existence.

The scientific community led by the NASA and Johns Hopkins University decided to take matters into their own hands and use the growing knowledge of asteroids to test the effectiveness of the kinetic impact method against an asteroid. This technique aims to transfer the angular momentum of a kamikaze probe to the asteroid, without using an explosive charge.

we could think First of all which is a simple applied physics experiment, similar to the one we perform on a pool table. Nothing could be further from the truth.

DART hit Dimorphos at a speed of 6.14km/s. When we hit an asteroid at hypervelocity, some of the collision is transmitted elastically, but as a crater is excavated, additional momentum is created due to the delivery of material in the direction opposite the projectile. This “recoil” component contributes to the momentum provided to the asteroid and contributes very effectively to diverting it from its trajectory. Indeed, the materials ejected after the impact created multiple particle filaments this could be tracked with telescopes from the ground and even from space.

The good news of the results that are revealed today is the great effectiveness demonstrated to deflect the asteroid. Dimorphos. In the paper led by Andrew F. Cheng, of the Johns Hopkins University Applied Physics Laboratory, we quantify the so-called Beta factor associated with this inelastic component which causes the recoil and which plays in favor of the increase in the effects of a kinetic impactor.

In fact, the experiment far exceeded expectations as the angular momentum transfer multiplier factor associated with the inelastic component of the deflection reached a value of 3.6. This means that the contribution at the time of this recoil by particle ejection greatly exceeded the incident momentum of 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 revealed by the images.

Consequence of the diversion, let’s not forget that the objective was shorten the orbital period of Dimorphos around Didymos by just over a minute, but it has been reduced by 33 minutesas detailed in the article led by Cristina A. Thomas University of Northern Arizona. It describes observations made to quantify this orbital period based on photometric observations made of the binary system using the largest telescopes available.

In another book, edited by Jian Yang Li of Tucson Institute of Planetary Sciences, In Arizona, the evolution of the filaments populated by the particles ejected after the excavation of the impact and which evolved over the months subjected to the radiation pressure of sunlight have been studied. The results are of great relevance for understanding what happens to materials that detach after impact and how long they remain around them.

These results encourage the effective development of planetary defense to act against any asteroid detected in a future direct collision course with our planet. Precisely in the article directed by Terik Daly, also of Johns Hopkins University Applied Physics Laboratorywe describe the magnitude of the scientific milestone to be achieved hitting Dimorphos with a robotic, autonomous probe like DARTas well as describing in detail the discoveries made about the nature of Dimorphos and the impact site.

Yet the key to our ability to deflect asteroids will be continue to invest in the early detection of all bodies that represent a real danger. Although this is not an easy task, thanks to the revolution in CCD digital camera technology, we can discover hundreds of them each year and, no less important, track and trace the movements of those already known.

Currently, monitoring programs, initially encouraged by NASA, show that there are some 31,361 asteroids and 119 comets in near-Earth space and that, at some point, one could be identified on a likely future collision course with Earth. In fact, this has already happened in six timesbut with the caveat that this has happened with asteroids a few meters in diameter which more often impact our planet and generate meteorite falls.

We currently know more than 10,400 potentially dangerous asteroids like or larger than Dimorphs, and we need to add a significant percentage of smaller asteroids that remain to be discovered.

The main threats we face are smaller asteroids, around 150 meters in size, of which around 60% are still unknown, as well as some extinct comets like 2015 TB145, a rocky object 650 meters in diameter known as “Halloween asteroid”.

This 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 from the Moon, because it was very little reflective and following a very eccentric orbit, extended almost to the orbit of Jupiter. Such objects, capable of hitting our planet with much higher energy than a conventional asteroid, illustrate the diversity and complexity of the problem we face.

It is not possible to be catastrophic since all the efforts to discover and catalog these bodies allow better quantification of the frequency of impact and suggest that an event like Tunguska would occur every several centuries. They also suggest that, fortunately, kilometer asteroid impacts occur every several tens of millions of years. In any case, the catalog of the Sentinel program of the Center for the Study of Small Objects (CNEOS) of the Jet Propulsion Laboratory (JPL) ensures that, among the near-Earth asteroids listed, none is a source of risk over several centuries. So they are totally baseless these catastrophic news which we unfortunately become accustomed to with each relatively close encounter of an asteroid with Earth.

In the distant past, the Earth was born after countless 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 broader time scale of billions of years, scientific evidence shows that asteroid and comet impacts have played a key role in Earth’s history, especially in water transport and the evolution of life itself.

Currently, the flow of interplanetary matter is not negligible: each year, they reach the Earth approximately 100,000 tons And although most of it does not reach the Earth’s surface, it evaporates and becomes part of our atmosphere.

Perhaps due to the challenge of correctly interpreting the cataclysms caused from space, a large part of the population continues to underestimate this danger that hangs over humanity. Despite this, awareness of the impact of Tunguska on June 30, 1908 and its association with an asteroid which, although less than 50 meters in diameter, devastated 2,200 km2 of Siberian taigashould make us think.

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 and technological capacities, will be the key to our survival. .

*Article originally published by The Conversation – Josep M. Trigo Rodríguez is Principal Investigator of the Meteorites, Minor Bodies and Planetary Sciences Group, Institute of Space Sciences (ICE – CSIC)

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