NASA’s and Johns Hopkins Applied Physics Laboratory Double Asteroid Redirection Test (DART) mission was launched on November 24, 2021. DART will impact its target, the asteroid Dimorphos, on September 27 at 1:14 am CET, slightly changing its orbit. This is the first planetary defense mission designed to change the course of an asteroid. Josep M. Trigo-Rodríguez, an astrophysicist from the Institute of Space Sciences (ICE-CSIC) and member of the Institute of Space Studies of Catalonia (IEEC), participates in DART’s scientific team.

This mission seeks to demonstrate the ability to use a kinetic impact method to deflect potentially dangerous asteroids. DART will conduct an experiment to change the trajectory and speed of an asteroid in space, using the spacecraft itself for kinetic impact, without an explosive charge. Doing so NASA will test planetary defence capabilities for future possible scenarios.

“With the DART mission we intend to better understand the key aspects that influence the transfer of kinetic momentum by a projectile without an explosive charge. It is a physical experiment to know the efficiency in which a kamikaze projectile excavates a crater in an asteroid, launching materials from the asteroid's surface in the opposite direction to the incoming projectile", says astrophysicist Josep M. Trigo-Rodríguez, from the Institute of Space Sciences and the Institute of Space Studies, who has been part of the scientific team of the DART mission since 2019. “The greater the efficiency of the process, the greater the deviation of the asteroid, but there is a multiplicative factor in the process of impact excavation that can be better understood from this experiment”, he adds.

Infographic showing the effect of DART's impact on the orbit of Dimorphos Credit: NASA/Johns Hopkins APL

The ICE-CSIC Meteorites, Minor Bodies and Planetary Science Group includes experts in the physical-chemical properties of asteroid and comets surface materials contributing profusely in this field. "The ICE-CSIC and the IEEC have carried out a series of experiments to better understand the mechanical properties of the regolith and the shock processes experienced by the asteroids to help understand their nature and mineralogy," says Dr.Trigo-Rodríguez. “Asteroids have a diverse structure, as a result of the continuous bombardment by projectiles since their formation. Because of that, deflecting them creates a major scientific-technological challenge”, he adds.

DART’s target is 11 million km from Earth: the binary asteroid system composed of Didymos (with a 780-m diameter) and Dimorphos (with a 160-m diameter), which orbits Didymos. Neither currently poses a threat to our planet, although it is classified as a Potentially Hazardous Asteroid. Didymos orbit has been studied in detail since its discovery in 1996 and it is considered as a prototype of the rocky bodies the Earth could face in the future.

After the impact, DART will transfer its kinetic momentum slightly shortening Dimorphos’ orbit. DART mission research team will quantify the crater's excavation efficiency by studying the satellite's new period of revolution through photometric light curve studies using some of the world's largest telescopes. In turn, the team will compare DART’s kinetic impact with Dimorphos computer simulations of kinetic impacts on asteroids. In this way, the team will be able to assess the effectiveness of this mitigation approach, as well as the accuracy of the simulations to see how closely they reflect the behaviour of a real asteroid.

In scientific papers prior to the DART spacecraft impact, Dr. Trigo-Rodríguez has helped predicting the nature and properties of Dimorphos's formative materials, which are key to understanding the consequences of DART’s impact with Dimorphos. “We are also awaiting the optical and spectral observations by DART and its LICIACube cubesat for a better interpretation. This robotic device will violently hit an asteroid whose internal structure we do not know, so the final scenario is still open”, he says.

Hera, the European future of the DART mission

“It should be taken into consideration that ESA’s Hera mission will follow DART. Therefore, it will be possible to accurately determine the point of impact and the consequences of crater excavation over the asteroid system (65803) Didymos”, points out Dr. Trigo-Rodríguez, who has been involved for more than a decade in different asteroid hazard mitigation proposals that preceded DART– ESA's Asteroid Impact Mission (AIM) and the Asteroid Impact Deflection Assessment (AIDA)– and he is also involved in the ESA’s Hera mission.

Hera is a European Space Agency (ESA) mission that will visit the binary asteroid Didymos as a follow-up of NASA’s DART to map Didymos and Dimorphos in high resolution. It is also planned to use CubeSat technologies to collect complementary information to mitigate future encounters with asteroids.

After the impact, Dimorphos orbital period will change and will be quantified, but many other details to better understand this binary asteroid will require an additional mission. This is why ESA is building Hera – to study the impact crater and its consequences on Dimorphos. Likewise, it will allow to rebuild its shape with precision, characterize its composition, structure and nature.