Clearest images yet of interstellar visitor 3I/ATLAS show icy nucleus and long tail

Astronomers on Friday released the clearest images to date of the interstellar object 3I/ATLAS, showing a dense icy nucleus surrounded by a broad coma and a distinct tail that astronomers say is consistent with cometary activity rather than an engineered craft.

The observations, taken at the Gemini South Observatory in Chile on Aug. 27 when the object was about 240 million miles (380 million kilometres) from Earth, show a multi‑colour view of 3I/ATLAS and a tail stretching in the anti‑Sun direction. The object is moving through the solar system at about 137,000 miles per hour (221,000 km/h). The tail subtends roughly one‑120th of a degree on the sky, a size astronomers say matches expectations for dust and gas pushed away from the nucleus by solar radiation and outgassing.

The Gemini images are among the first multi‑colour ground‑based photographs of the visitor and show the classic components of an active comet: a compact, bright central condensation identified as a frozen nucleus, a surrounding halo of gas and dust known as a coma, and an extended tail directed away from the Sun. That morphology is central to the prevailing interpretation among planetary scientists that 3I/ATLAS is a large, frozen interstellar comet undergoing sublimation of volatile ices as it approaches the inner solar system.

Archival data from NASA's Transiting Exoplanet Survey Satellite (TESS) indicate the object could have been detected months earlier than its official discovery. Researchers examining TESS imagery found 3I/ATLAS in observations dating back to May 7 and tracked it through June 3. During that interval the object brightened by a factor of about five, a change that investigators say exceeds the roughly 1.5‑fold increase expected from the change in distance alone and has prompted additional scrutiny of its activity.

3I/ATLAS was first publicly reported after an initial detection by a NASA telescope on July 1. Since then, teams using a range of facilities have monitored its trajectory and spectral properties. Observations have identified emissions consistent with the release of carbon dioxide and other volatiles, a behaviour typical of active comets arriving from cold interstellar space.

A minority of researchers have argued that some aspects of the object's behaviour merit alternative explanations. Harvard astrophysicist Avi Loeb, a prominent and sometimes controversial proponent of the possibility of extraterrestrial technology, has published a paper suggesting 3I/ATLAS may be accompanied by an unseen "precursor mini‑probe" travelling ahead of the main body. Loeb contends that an artificial object could in principle adjust the course of a small probe to perform close passes of planets.

Loeb's paper notes that on Oct. 3, 2025, 3I/ATLAS is projected to pass within about 18 million miles of Mars — close enough for high‑resolution imaging by spacecraft such as Mars Reconnaissance Orbiter's HiRISE camera to resolve fine structure if present. He wrote that if a technological probe exists and were to change course near the encounter it could pass near or potentially impact Mars. Mainstream planetary scientists and mission teams have said they will monitor the approach but caution that available data to date are consistent with natural cometary processes.

Researchers say continued multi‑wavelength monitoring, including spectroscopy and imaging from ground and space telescopes, will be critical to refine the object's composition, activity drivers and any small fragments or companions. Such observations can quantify the amounts of carbon dioxide, water and dust being released, track changes in brightness and morphology, and test hypotheses about non‑gravitational forces that can alter an object's motion.

For now, the Gemini South images and the TESS archival detections strengthen the interpretation that 3I/ATLAS is an active interstellar comet. The object remains of high interest because interstellar visitors are rare: only a handful have been confirmed, and each provides a unique opportunity to study material formed around other stars. Observing campaigns are continuing as the object moves inward, and teams across the globe have pledged to share data to build the clearest possible picture of the visitor's origin and nature.