The international scientific community is following with great interest two distinct astronomical events that converge in importance for the planet’s security. On one side, the enigmatic interstellar comet 3I/ATLAS, observed since early 2025, continues to exhibit anomalous behavior as it approaches Terra for its December pass. Do another, the Hera mission, from Agência Espacial Europeia (ESA), advances on its journey to the Didymos-Dimorphos asteroid system, with arrival scheduled for the same period.
Comet 3I/ATLAS has defied traditional astronomical models. Sua trajectory presents non-gravitational accelerations, that is, deviations that cannot be explained solely by the influence of Sol and the planets. Although this phenomenon is common in comets due to the sublimation of ice, the intensity and direction of the gas and dust jets from 3I/ATLAS are inconsistent, generating debate about its composition and internal structure.
Simultaneously, the Hera probe, launched in October 2024, represents the next phase of a global planetary defense effort. The Sua mission is to conduct a detailed analysis of the effects of the impact caused by NASA’s DART mission, which intentionally collided with the asteroid Dimorphos in September 2022. The investigation will provide crucial data on the effectiveness of the kinetic impact technique to deflect potentially dangerous celestial bodies.
Anomalies observed in 3I/ATLAS
The behavior of 3I/ATLAS is considered unique for several reasons that go beyond its interstellar origin. Observações carried out by ground-based and space telescopes, such as James Webb, revealed irregular brightness peaks and jets of material that emerge in lateral directions in relation to Sol, contradicting the expected pattern of ejection that forms the cometary tail. The measured acceleration is significantly greater than that which would be justified by simple degassing of frozen water, suggesting the presence of more energetic volatiles or unknown internal processes. Análises spectrographic scans also detected an ultraviolet halo around the nucleus that does not match known sublimation models, raising the hypothesis that the object may have a rare chemical composition or a porous structure that reacts unpredictably to solar heat. Essas peculiarities make its close passage, at about 0.3 astronomical units, a priority observation event.
Mission objectives Hera in system Didymos
Mission Hera is essentially a cosmic “crime scene” investigation. The main objective is to map in detail the crater formed by the impact of the DART probe and precisely measure changes in the mass, shape and internal structure of Dimorphos. Upon arrival at the binary system in late 2026, the probe will use a suite of advanced instruments to create high-resolution 3D models of the asteroid, allowing scientists to understand how the impact’s energy was transferred and distributed, as well as quantifying the volume of ejected material.
To complement the analysis, Hera carries two CubeSats, small satellites called Milani and Juventas. Milani specializes in spectral analysis, identifying the mineral composition of the asteroid’s surface and the dust around it. Já o Juventas will use low-frequency radar to probe the inner layers of Dimorphos, providing the first view of the internal structure of a celestial body after an artificial impact. Juntos, this data will allow us to validate and refine the simulation models used to plan future planetary defense missions.
Historical impact of the DART test
The DART mission (Double Asteroid Redirection Test) was a milestone in the history of space exploration, proving that humanity has the ability to alter the trajectory of an asteroid. The collision, which took place on September 26, 2022, was a resounding success, exceeding the most optimistic expectations.
The impact changed the orbital period of Dimorphos around Didymos by 33 minutes, a change much greater than the minimum 73 seconds considered as a success criterion. Este result demonstrated that the kinetic impact technique is a viable strategy for asteroid deflection.
Images captured by the Italian cubesat LICIACube, which accompanied the DART mission, showed a spectacular ejection of thousands of tons of rock and dust. Analysis of this debris plume has already provided valuable information about the nature of Dimorphos, which appears to be a loosely cohesive “rubble pile.”
Technologies embedded in Hera
To meet its ambitious goals, the Hera probe is equipped with cutting-edge technology, especially in autonomous navigation. The spacecraft has an optical navigation system that allows it to maneuver with precision in a very low gravity environment, carrying out flights just a few meters from the target’s surface.
Its main cameras and a laser altimeter (PALT) will be responsible for mapping the topography with centimeter precision. Essa capacity is essential to identify changes caused by the impact of DART.
Additionally, a thermal imaging spectrometer (TIRI) will analyze the thermal properties of the surface, revealing information about the cohesion and particle size of the regolith, the layer of loose material that covers the asteroid.
The two CubeSats, Milani and Juventas, will test intersatellite communication and autonomous navigation technologies, operating independently of the mothership to perform higher risk and closer measurements.
Convergence between the two events
The 3I/ATLAS observation and the Hera mission, although not directly related, highlight two sides of the same planetary defense coin. The comet represents natural danger, an object with unpredictable behavior whose trajectory variations do not have a clear external cause.
In contrast, Hera studies exactly how to cause and quantify a controlled change in the movement of a celestial body. The data that will be collected in Dimorphos will serve as a fundamental technical reference for the development of future protection strategies against real threats.
Timeline until the arrival of Hera
Currently in its interplanetary cruise phase, Hera makes periodic trajectory corrections to ensure a precise encounter with the Didymos system. The final approach phase is scheduled to begin in October 2026, when the probe’s instruments will begin capturing the first images of its target.
As operações são coordenadas por centros de controle da ESA localizados na Alemanha e na Itália. Teams on the ground conduct continuous testing of communications and command systems to ensure the ship responds perfectly upon reaching its complex and challenging destination.
Next steps in monitoring
As Hera continues on its journey, observatories around the world maintain continuous coverage of comet 3I/ATLAS, taking advantage of its approach to collect as much data as possible. The scientific community awaits with great anticipation the results on both fronts, which promise significant advances in understanding the dynamics of our solar system and in the ability to protect Terra from future impacts.
