Astronomers detect a pulsing sunward jet from interstellar object 3I/ATLAS

The Anti-Tail of 3I/ATLAS Wobbled Before Perihelion reports new observations of the interstellar object 3I/ATLAS by Avi Loeb, based on ground-based telescope data collected in mid-2025.

The article summarizes the results of a peer-reviewed paper that analyzes images taken over several weeks and identifies a recurring change in the direction of a narrow, sunward jet, known as an anti-tail.

The reported motion follows a regular pattern, described as a wobble, with a measured period of about eight hours.

The context of the report is the ongoing study of rare interstellar objects that pass through the solar system.

Because these objects originate outside the Sun’s gravitational influence, they provide information about physical processes beyond the solar system.

Observations of 3I/ATLAS were made between July and September 2025 using the Two-meter Twin Telescope in Tenerife, Spain.

The data include repeated measurements of the jet’s position angle at a fixed distance from the object’s brightness peak.

The article also places these findings alongside earlier measurements of brightness variation, timing the object’s closest approach to Earth, and public interest in the object.

Together, the observations aim to describe the object’s rotation, activity, and geometry using available data.

Detection of a periodic jet wobble in 3I/Atlas

The main scientific result described is the detection of a periodic change in the direction of the anti-tail jet of 3I/ATLAS. According to the paper, the jet shows a repeating modulation with a period of 7.74 ± 0.35 hours.

The article explains that this pattern is consistent with a jet emitted from a location offset from the object’s rotation poles, causing the jet direction to trace a cone as the nucleus rotates.

The authors describe the effect using a comparison: the jet motion is “just like the rotating light beam of a lighthouse or a pulsar.”

Measurements were taken at a projected distance of 6,000 kilometers from the brightness peak, allowing for consistent tracking of the jet angle across multiple nights.

The article notes that this is “the first periodic jet-angle modulation detected in an interstellar object.”

The derived jet period is linked to the object’s rotation. If the jet comes from a single active region near a pole, the implied rotation period is about 15.5 hours.

This value is close to an independently measured brightness variation period of 16.16 hours reported earlier.

The agreement between these measurements supports the interpretation based on rotational motion rather than random activity.

Observations, timing, and broader context 

The article places the jet analysis within a broader observational timeline. Images were collected over 37 nights between July 2 and September 5, 2025, using sidereal tracking and stacked exposures.

The anti-tail appears faint but persistent, maintaining an almost constant average position angle with small periodic deviations. The mean jet direction is used to estimate the sky-projected orientation of the rotation axis.

The report also notes an upcoming observational opportunity. On December 19, 2025, 3I/ATLAS is expected to reach a closest approach distance of about 269 million kilometers.

The timing coincides with a New Moon, reducing sky brightness and allowing clearer observations. The article states that “the data collected around that time by multiple telescopes on Earth and in space will educate us about the qualities of our latest interstellar visitor.”

In addition to technical results, the article includes excerpts from two messages received by the author. One reader writes,

“Thank you for reminding the world that science should be an adventure into the unknown,” while another notes that historical examples show “a greater attachment to the received hypothesis than to data.”

These comments are presented as part of the public response to ongoing observations of 3I/ATLAS.
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