New measurements indicate that 3I/ATLAS, the third interstellar object confirmed to visit Sistema Solar, has experienced a significant acceleration in its rotation. Após its closest approach to Sol, known as perihelion, on October 29, 2025, the celestial body began to complete one revolution around its own axis every 7.1 hours. The discovery was made possible thanks to a detailed analysis of data collected by Telescópio Espacial Hubble and a ground-based observatory.
The research, led by astrophysicist Abraham Loeb in a collaboration with amateur astronomer Toni Scarmato, used observations taken between November and December 2025. The change in rotational speed offers valuable clues about the composition and behavior of objects formed in other star systems when exposed to heat and radiation from our star.
This phenomenon reinforces the importance of continuous monitoring of interstellar visitors. Cada observation provides crucial data for understanding the complex dynamics that govern these bodies, revealing how interaction with Sistema Solar’s environment can drastically alter its physical characteristics, such as the speed of rotation and the activity of its surface.
Dual methodology for accurate measurement
To determine the new rotation period with high confidence, scientists employed two distinct and independent techniques, the results of which proved remarkably consistent. The first approach involved analyzing images of Telescópio Espacial Hubble, captured between November 20 and December 27, 2025. The researchers applied advanced image processing, known as the Larson-Sekanina Rotational Gradient filter, which removes the symmetrical glow of the object’s coma and highlights the structure of the gas and dust jets expelled by it. Essa technique allowed measuring the position angle of the main jet, revealing a periodic oscillation that corresponded to a rotation period of 7.20 hours, with a small margin of error of 0.05 hours, indicating the precession of the jet around the axis of rotation.
In parallel, an observation campaign was conducted from a 0.25 meter telescope located at Calábria, Itália, between December 9 and 22, 2025. The data showed brightness modulations of up to 30%, which repeated every 7.136 hours, with an even greater precision of just 0.001 hour. Combining the two results, obtained using completely different methods, led the team to establish the average post-perihelion rotation period at 7.1 hours. The small discrepancy between measurements is attributed to systematic effects inherent to each technique, but the general agreement provides great robustness to the research conclusion.
The acceleration caused by the solar passage
Comparing the current rotational period with measurements taken before 3I/ATLAS passed through perihelion reveals a dramatic change. Observações previews indicated a much longer period, estimated between 16 and 17 hours, based on variations in brightness.
The main hypothesis for this acceleration is the intense activity generated by the proximity to Sol. Heating the object’s surface may have activated new regions, causing jets of material to be expelled from a second rotational pole that was previously inactive.
This activation of jets on opposite sides of the object effectively doubled the frequency of Terra’s observed brightness modulations. What was once seen as a 16-hour cycle now manifests as an approximately 7-hour cycle, explaining the apparent halving in the rotation period.
The third visitor from another star system
3I/ATLAS was first identified in July 2025 and its trajectory quickly confirmed its extrasolar origin, making it the third known interstellar visitor to cross our Sistema Solar. Sua hyperbolic orbit, which will take it back to deep space without returning, is the signature of an object that is not gravitationally bound to Sol. Sua’s closest pass to our star occurred at a distance of about 1.4 astronomical units (AU), a safe distance but sufficient to trigger notable cometary activity. Diferentemente From its predecessors, the enigmatic 1I/’Oumuamua (2017) and the cometary 2I/Borisov (2019), 3I/ATLAS stood out for displaying an extremely well-defined and active coma and jets of material, providing astronomers with an unprecedented opportunity to closely study the composition of a body formed around another star. Continued observations with Hubble, beginning soon after its discovery, have created one of the most complete data sets ever obtained for an object of this class.
An unusual alignment with the Sol
One of the study’s most intriguing findings was the alignment of the 3I/ATLAS rotation axis. Measurements indicate that the axis is aligned with the line connecting the object to Sol, with a margin of just 20 degrees.
This configuration is considered statistically rare, with an estimated probability of occurring by chance between 1.5% and 6%. The Tal alignment suggests that the object’s rotational state was established long before its entry into the cold, vast interstellar space.
What Brightness Variations Really Mean
The research clarifies a fundamental point about the nature of the brightness variations observed in 3I/ATLAS. Contrary to what one might assume, these modulations are not caused by the irregular shape of the object’s core.
Analysis of high-resolution images from Hubble indicates that less than 1% of the light we detect originates directly from reflection off the surface of the rocky or icy core.
The real source of the variability is the dense cloud of gas and dust, the coma, and the jets that are expelled from it. The precession of the rotation axis causes the orientation of these jets to change relative to our line of sight.
This change alters the amount of dust between the object and Terra, generating periodic fluctuations in brightness. The phenomenon was described by researchers as a “heartbeat” in the ejection of material, dominated by the dynamics of active jets.
Unique observation opportunity in January
Astronomers await with great anticipation January 22, 2026, when 3I/ATLAS will reach a position of almost perfect opposition. Nesse celestial event, the Terra will be positioned directly between the Sol and the interstellar object.
This unique orbital geometry will cause the jet pointing in the direction of Sol to be aimed precisely at the telescopes at Terra. Isso will offer an unprecedented head-on view of the jet’s internal structure, enabling detailed studies of its composition and dynamics.
Continuous monitoring of the cosmic traveler
As 3I/ATLAS continues its journey away from Sol, away from our Sistema Solar never to return, space and ground-based telescopes remain vigilant. Novas observations are scheduled for the coming months, with the aim of verifying whether the 7.1-hour rotation period remains stable or undergoes further changes as the object’s activity decreases with distance.