2024-01-31 09:15:33
Near-Earth Asteroids (NEAs) are those that come within 200 million kilometers of our planet. Most are harmless and don’t get too close. But others, due to their size and the short distance they reach, represent a potential threat due to the consequences of a possible impact against the Earth’s surface.
That is why a large part of the world scientific community and space agencies such as the European Space Agency (ESA) and NASA have monitoring and study programs for these celestial objects.
There are various types of asteroids according to their spectrum and composition. Due to their internal structure, we can differentiate between monolithic asteroids and those that are “piles of rubble”. The main characteristic of the latter is that they were formed from the remains left by the catastrophic collision between large asteroids. They are, literally, an agglutination of individual and irregular rocks, which are only held together by gravitational attraction and frictional forces.
In general, debris pile asteroids are small, with diameters less than ten kilometers. According to the most accepted theory, when the speed of rotation on its axis is very high (less than 2.2 hours), the centrifugal force is greater than the gravitational force and, consequently, they would tend to expel material. But in certain cases this has not been observed. One of the questions, still unanswered, is: how do they manage to maintain their shape and why do they not disintegrate?
A new investigation has focused on a binary asteroid system located, in the section of its route closest to Earth, about ten million kilometers from it.
The research has been led by Nair Trógolo, an astronomer at the Córdoba Astronomical Observatory (OAC), dependent on the National University of Córdoba (UNC) in Argentina, and a scholarship holder from the National Council for Scientific and Technical Research (CONICET) of Argentina.
The aforementioned binary asteroid system is composed of Didymos (the main one, 780 meters in diameter) and Dimorphos (only 160 meters in diameter). The second is orbiting the first.
The choice of this binary system as an object of study is not accidental. NASA and ESA jointly sent the DART space probe and will send another, Hera, to study its composition and internal structure.
The study carried out at the Córdoba Astronomical Observatory (OAC) has a fundamental objective for the agencies that will send the Hera mission: to know if Didymos is ejecting material out of its orbit, which would allow the probe’s trajectory to be programmed to protect it from possible collisions with these fragments scattered in nearby space.
With computer simulations, Trógolo analyzed the forces to which a rock fragment on the surface of the main asteroid is exposed, particularly in the equator area.
For that region he was able to determine that if the centrifugal force caused by the rotation (the one that tends to “throw” the rock in the example into space) was greater than the gravitational force (the one that tries to keep the rock stuck to the surface), that rock It lifted off from the surface and began to orbit the asteroid for a while. However, practically, most of the time that boulder fell back on the asteroid.
“That is, Didymos could be constantly losing rocks from the surface. Now, what happens to them next? In 97% of cases they land again on the surface of Didymos, from where they will end up taking off again, in cycles of ejection and fall, thus maintaining a certain balance in the system,” Trógolo explains to Argentina Investiga.
Tests with the numerical codes also revealed that in the ejection phase a few stones continued their journey and landed in Dimorphos, while others fled the system completely. The largest rocks, meanwhile, remained orbiting Didymos, forming a thin disk of stone matter at the equator,” says the scientist.
“In the simulations we observe a disk around the asteroid that is not very stable, which remains there because there is an exchange of particles all the time: while some are constantly ejected, others return to the surface, others leave the system and others fall into the secondary asteroid,” Trógolo summarizes.
The results obtained in this new study could be confirmed with data from the DART (Double Asteroid Redirection Test) mission, which consisted mainly of a programmed collision against one of the asteroids, with the purpose of trying to modify the orbit of a celestial body in space.
NASA’s DART space probe left Earth on November 24, 2021. DART traveled accompanied by a small CubeSat designed to capture images of the collision, called Licia CubeSat.
After 10 months of traveling through space, the DART, weighing about 570 kilograms, successfully impacted the asteroid that was its attack target: Dimorphos, the small asteroid of that binary system. She did so on September 26 (or early on the 27th in other time zones), at a speed of approximately 22,000 kilometers per hour.
The images captured at that time are still being analyzed, but they could provide the first clues to verify the material ejection hypothesis proposed in the research conducted by Trógolo.
The definitive answer will come in 2026, when the Hera probe reaches the binary system to study it up close.
Artist’s recreation of NASA’s DART spacecraft and the small LICIACube spacecraft (below right) of the Italian Space Agency (ASI). The images of the asteroids Dimorphos and Didymos that appear next to the spacecraft are real and were obtained by the DART spacecraft. (Image: NASA Johns Hopkins APL / Joshua Diaz)
Deflecting asteroids
Scientific groups, together with citizen science programs coordinated by space agencies in all parts of the world, are working to identify and track asteroids that could impact Earth. To prevent these catastrophic events, surveillance programs were developed, such as NASA’s Near-Earth Object.
Most NEAs are small and do not pose a significant threat. However, there are a small number of “potentially dangerous objects” that have a diameter greater than 140 meters and an orbital path that brings them quite close to our planet. These are monitored permanently.
A possible solution to avoid a collision would be to alter the asteroid’s course using techniques based on gravity or kinetic energy. Broadly speaking, it would be about changing the trajectory of an asteroid by colliding a spacecraft against it. Currently, this alternative is considered a viable option to protect the Earth from possible impacts in the future.
The study carried out by Trógolo and his colleagues is titled “Lifted particles from the fast spinning primary of the Near-Earth Asteroid (65803) Didymos”. This work was developed during a research stay at the University of Alicante, Spain, together with members of the NASA DART mission research team.
In addition to Trógolo, the study is also signed by Adriano Campo Bagatina and Paula G. Benavideza, from the University of Alicante in Spain, and Fernando Moreno, from the Institute of Astrophysics of Andalusia (IAA), dependent on the Higher Council for Scientific Research (CSIC). in Spain. (Source: Victoria Rubinstein / National University of Córdoba / Argentina Investiga)
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