It is difficult to think that our existence can suddenly be put in check by a celestial phenomenon. In fact, our ignorance about the danger associated with the impact of asteroids denotes the naivety of our species in the XXI century. Many of us specialists think that the impacts of asteroids and comets have played a key role in the history of the Earth and probably also in the evolution of life. Paradox of our existence is that, in our contemporary history, we have not identified at a popular level the cataclysms caused from outer space.
Despite this, the awareness of the impact of Tunguska on June 30, 1908 and its possible association with a small asteroid of about 50 meters that devastated 2,200 km² of taiga should make us reconsider, as we intend with that international initiative known as Day of the asteroid. The monitoring programs, initially encouraged by NASA, show us that there are some 30,000 asteroids in the space near Earth and that, at some point, a catastrophe could occur. Today we know of more than 10,200 potentially dangerous asteroids, as large or larger than Dimorph, the asteroid hit by the NASA/JHU DART probe. However, it is not possible to be catastrophic, given that the new discoveries made with various techniques that allow better quantification of impacts suggest that an event like Tunguska’s could occur every several centuries. They also tell us that, fortunately, impacts by kilometer-sized asteroids occur every several tens of millions of years. The program catalog Sentry of the Center for the Study of Smaller Objects (CNEOS) of the Jet Propulsion Laboratory (JPL) assures that, among the cataloged near-Earth asteroids, none is a source of risk on a scale of several centuries.
The main threats we face are asteroids smaller than about 150 meters, of which we still do not know about 60%, and also certain extinct comets, such as 2015 TB145, a rocky object 650 meters in diameter. known as a “skull asteroid”. Discovered three weeks before its passage on October 31, 2015, a little more than the distance from the Moon, due to its eccentric orbit extended almost to the orbit of Jupiter, it could have deposited an impact energy much higher than that of a nearby asteroid to the earth. When a comet extinguishes its activity, it transforms into a dark body, difficult to detect.
Until now, the best defense has been the robotic telescopic tracking programs that discover the objects finally cataloged by the Minor Planet Center. Planning a monitoring system with space telescopes in the infrared range with wide-field cameras would facilitate the discovery of such unexpected “monsters”. In addition, they would make it possible to discover all the objects of a few hundred meters that cross the region near the Earth without the observational bias imposed on ground-based telescopes by the apparent movement of the Sun in the celestial vault throughout the year.
But, what would happen if we discovered one en route to a direct impact on our planet? To move into an active role we would need to have at least one Kinetic Impactor-style mission ready whose basic concept NASA has tested with DART. That would allow us to deflect asteroids from several tens to a few hundred meters. Other alternatives have been devised for larger objects, but have never been put into practice and involve much higher costs. To apply them we need to improve new techniques to understand their physical and compositional properties. From the Institute of Space Sciences (CSIC-IEEC) we are applying new techniques to better understand asteroids, based on the study of the mechanical properties of meteorites and the samples that the return missions provide us.
In short, NASA’s DART mission has made history by completing the first in situ experiment to deflect an asteroid by impacting the satellite of the binary asteroid Didymus. Yesterday we came face to face with the enemy: a huge rock stack 160 meters in diameter called Dimorfo. In the next few days we will check if the DART probe in its kamikaze mission has efficiently transferred its angular momentum to Dimorph, boosting it slightly and changing its orbital period around Didymus by a few minutes. Later, with the Hera mission of the European Space Agency (ESA) we will investigate both asteroids, the crater excavated by DART and we will complete a more detailed study of its structure and composition. Because in order to deflect an asteroidal enemy, you have to know him well.
Josep Maria Wheat is an astronomer, researcher at the Institute of Space Sciences (CSIC) and the Institute of Space Studies of Catalonia.
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