On September 27, 2022, NASA’s DART (Double Asteroid Redirection Test) mission collided with its target, the asteroid Dimorph, and changed its orbit.
This was the first planetary defense test mission designed to change an asteroid’s course, and its success was followed by intensive analysis of the collision, which includes studying the tons of rock that were displaced and flung into space.
The results of these analyzes are published today in four articles in Nature, which included the participation of researchers from the Institute of Astrophysics of Andalusia (IAA-CSIC) and the Institute of Space Sciences (ICE-CSIC).
The DART mission sought to demonstrate the usefulness of the kinetic impact method to deflect potentially dangerous asteroids without using explosive charges. Its target, located 11 million kilometers from Earth, was the dimorphic satellite, about 160 meters in diameter, which orbits the asteroid Didymus (780 meters in diameter), forming a binary system.
The DART spacecraft sought to demonstrate the usefulness of the kinetic impact method to deflect potentially dangerous asteroids without the use of explosive charges.
The impact of the ship, which was traveling at about six kilometers per second, deviated Dimorph’s orbit and shortened its translation period relative to Didymus by more than half an hour, which was a success for the project.
“However, many other aspects remained to be studied, namely the characterization of the material ejected after the collision”, says Fernando Moreno, a researcher from the IAA-CSIC who participates in one of the articles.
Thus, from the moment of impact and until several months later, the Hubble Space Telescope (HST) captured images of this material and characterized its evolution.
The CSIC researcher clarifies: “Although part of the material consists of particles ejected at high speed, at several hundred meters per second, and which quickly disappear from the field of view of the cameras, we were able to observe the low-velocity component.”
This article presents a fundamentally morphological study of the evolution of this material, which allowed us to determine the complex interaction between the asteroid system and the dust under the action of radiation pressure produced by sunlight.
This work made it possible to determine the complex interaction between the asteroid system and the dust under the radiation pressure produced by sunlight.
“When DART excavates the impact crater, the surface and subsurface structure of the asteroid plays an important role. Large rocks are thrown out, but for the most part, we saw that many were weakened by spatial processing on the asteroid’s surface and therefore were preferentially crushed by the impact and immediately flung into space in the opposite direction of the projectile. as centimeter to micrometer-sized particles, which are then subjected to the radiation pressure of sunlight itself,” points out Josep Maria Trigo, a researcher at ICE-CSIC in Barcelona and also a co-author of the study.
“This radiation pressure pushes micrometer particles to distances of several thousand kilometers in a few days, while the larger particles, ejected at speeds close to the system’s escape velocity (about forty centimeters per second) show spiral motions around the system and a complicated evolution over the days”, indicates Moreno.
“We see, for example, the appearance of a double tail, which may be related to the re-impact of a portion of the largest particles or boulders emitted on the surface of Didymus, or to the disintegration of these same boulders due to high rotational speeds or due to mutual collisions”, he points out.
Asteroid activation is a phenomenon that occurs naturally in the Solar System and produces an increase in object brightness and the deployment of a dust tail similar to that of comets. The DART experiment will help characterize naturally active asteroids in which collisions with other asteroids act as a trigger mechanism.
Great efficiency in deflecting asteroids
On the other hand, Trigo, a member of the Institute of Space Studies of Catalonia (IEEC) at ICE-CSIC, studied and interpreted the Dimorpho images obtained by the Draco camera on board the DART and also the Italian probe LICIACube, as well as the effects produced in the Binary system environment from some of the largest telescopes on Earth and in space before and after impact.
The specialization of the ICE-CSIC team in the chondritic meteorites that make up these asteroids has improved the interpretation of the processes that occur in them.
The CSIC researcher also contributed to quantify the impulse factor produced by the DART crash, the so-called beta factor, participating in three of the four articles published by Nature.
Scientists have found that a probe like DART, based on a technique known as a kinetic impactor to deflect asteroids, has great potential to be effective.
“Through these images we verified the effects caused by the impact of the DART. For several weeks, measurements of Dimorph’s period of revolution were hampered by the enormous amount of dust emitted by the DART crater. We cannot forget that Dimorfo is enormously fractured by colossal impacts and seems to have a fragile structure like a pile of rubble, with the density and porosity of the material being fundamental factors when it comes to quantifying the beta factor”, highlights Trigo.
Scientists have found that a probe like DART, based on a technique known as a kinetic impactor to deflect asteroids, has great potential to be effective. “Humanity now has a plan in case it discovers an asteroid on a direct collision course with Earth. In fact, we can say that DART inaugurated a new era of active planetary defense against the danger of asteroid impacts”, he concludes.
The DART mission’s observations will yield more results soon. “We will characterize the ejected material with the application of dynamic Monte Carlo codes, which allow us to study the dynamic evolution of particles and build synthetic images, which in turn reveal the properties of the dust: size distribution, velocities and total mass ejected ” , points out Fernando Moreno.
Soon we will be able to go even deeper into the dynamic origin and collisional evolution of these bodies, representative of those that can compromise life on Earth.
Josep Maria Trigo
“This is very important to determine the so-called beta factor in the efficiency of transmission of linear momentum in the collision, in addition to the knowledge it conveys about the natural processes of collision in the asteroid belt”, he specifies.
“Soon we will understand the structure, composition and porosity of both asteroids, thanks to the arrival in this binary system of the Hera mission of the European Space Agency (ESA), which will allow us to deepen even more the dynamic origin and collisional evolution of these bodies, representative of those that can jeopardize life on Earth”, points out Trigo.
The Applied Physics Laboratory (APL) at Johns Hopkins University (USA) built and operated the DART spacecraft and manages the DART mission for NASA’s Planetary Defense Coordination Office as a project of the US agency’s Office of Planetary Mission Programs. LICIACube (Light Italian Cubesat for Imaging of Asteroids) is a mission of the Italian Space Agency (ASI) that is part of the DART mission carried out by Argotec.
The properties of the crater generated on the surface of Dimorpho, as well as the evolution of the dynamics of the system, will be studied by the Hera mission of the European Space Agency (ESA), which will be launched in 2024 and will begin the study of the system in 2026. .
References:
Cheng A, et al. “DART Mission Kinetic Impact Momentum Transfer on Asteroid Dimorphos”, Nature (2023)
DalyT., et al. “Successful kinetic impact on an asteroid for planetary defense”. Nature (2023)
Li J.-Y., et al. “Eject from active asteroid Dimorphos produced by DART”. Nature (2023)
