Image of interstellar comet 3I/ATLAS (C/2025 N1). The original image is shown on the left and the same image after processing to enhance the structures of the inner coma is shown on the right. A narrow jet of material can be seen emerging from the region illuminated by the Sun, clearly distinct from the dust tail, which extends in the opposite direction to our star. The arrows indicate the direction of the comet's movement and the antisolar direction. The cross marks the centre of the comet. Credit: TTT (Light Bridges) / IAC
The discovery, made in collaboration between the IAC Solar System Group and Light Bridges, reveals the rotation period of comet 3I/ATLAS
The Two-metre Twin Telescope (TTT) has made a pioneering discovery in astronomy: the first detection of a jet of gas and dust and its periodic modulation in an interstellar comet, 3I/ATLAS.
The study, published in the journal Astronomy & Astrophysics, provides the first evidence of localised activity from an interstellar nucleus, offering unique insight into the nature of a celestial body that formed outside our Solar System.
An extraordinarily normal interstellar comet
The research was led by Miquel Serra-Ricart, scientific director of Light Bridges. The co-authors are Javier Licandro, researcher at the Instituto de Astrofísica de Canarias (IAC), and Miguel R. Alarcon, pre-doctoral researcher at the IAC and director of scientific operations at Light Bridges.
Miquel Serra-Ricart emphasises the importance of this milestone: ‘In July, based on the variability in the brightness of the coma, we were the first to talk about its rotation period of around 17 hours, and now we are reporting the first jet in an interstellar comet, which also confirms the rotation calculated in July,’ he explains.
Serra-Ricart also highlights the surprising familiarity of the object, despite its origin: ‘3I/ATLAS is an extraordinarily normal interstellar comet. The detection of this jet allows us to make a direct comparison with the mechanisms of activity observed in comets in our own Solar System,’ he says.
‘Characterising jets in a body such as 3I/ATLAS represents a unique opportunity to investigate the physical behaviour of a pristine body formed in another planetary system,’ comments Licandro.
Processed images of the inner coma of interstellar comet 3I/ATLAS (C/2025 N1) obtained during different nights with the TTT. Image processing allows us to identify a narrow jet of material emerging from the Sun-illuminated core area, clearly differentiated from the dust tail, which extends in the opposite direction. The superimposed lines indicate the orientation of the jet and allow us to infer the direction of the comet's axis of rotation. The arrows indicate the direction of the comet's movement and the antisolar direction, while the cross marks its centre. Credit: TTT (Light Bridges) / IAC
Discovery and rotation of the nucleus
The key observations were made with the Two-metre Twin Telescope at the Teide Observatory in Tenerife during an intensive 37-night campaign between July and September 2025 for the PLANETIX25 project. The team pushed the storage and computing capabilities of ASTRO POC, a public-private astrophysical computing infrastructure, to their limits to focus on the structures of the inner coma of 3I/ATLAS, the third confirmed interstellar object.
Using an image filtering technique known as Laplacian transformation, the research team detected a faint but distinct jet of gas and dust emanating from the nucleus. This is the first evidence that an interstellar nucleus exhibits such a focused release of material.
The most significant finding is that the jet did not remain static. A detailed analysis of its position revealed a small but significant periodic modulation around the nucleus's axis of rotation. This oscillation of the jet, the first of its kind detected in an interstellar comet, allowed the team to deduce the nucleus's rotation period. It was concluded that the rotation period of comet 3I/ATLAS is between 14 and 17 hours if the jet originates near one of the poles, confirming the measurements made last July with data from the TTT by researchers from the IAC, the Gran Telescopio Canarias (GTC or Grantecan) and the Complutense University of Madrid.
Scientific significance
Cometary jets are key tracers of core activity and its state of rotation. The methodology that enabled this discovery was optimal image filtering, which enhances the faint and anisotropic structures of the jet against the bright background of the coma. This advanced analysis contributes significantly to understanding how volatiles and dust behave in bodies such as 3I/ATLAS, which have travelled through interstellar space and contain material originating from the formation of a foreign planetary system.
Light Bridges
Light Bridges is a private research institution established in the Canary Islands, one of the best astronomical locations in the world. As such, our activity is focused on observational astronomy and data management. Our vision is advancing scientific knowledge while promoting both environmental and financial sustainability. We manage the newest robotic telescopes in the Teide Observatory —part of the Instituto de Astrofísica de Canarias (IAC)— alongside Astronomy High-Performance Computing Centers.
Artículo: M. Serra-Ricart, J. Licandro, M.R. Alarcon.“Pre-perihelion detection of a wobbling high-latitude jet in the interstellar comet 3I/ATLAS”, A&A, 2025. DOI: https://doi.org/10.1051/0004-6361/202558072
Contacto:
Javier Licandro, jlicandr [at] iac.es (jlicandr[at]iac[dot]es)
Miquel Serra, miquel [at] lightbridges.es (miquel[at]lightbridges[dot]es)
