In December 2025, the interstellar object 3I/ATLAS (the third confirmed visitor from another star system) provided a series of stunning scientific revelations. New high-resolution images captured by the Hubble Space Telescope on December 12 and 27, 2025, have revealed a complex "wobbling" double-jet structure that is challenging our understanding of interstellar matter.
1. The December Observations: A Tale of Two Jets
As 3I/ATLAS recedes from the Sun following its October 29 perihelion, Hubble re-observed the object using its WFC3 UVIS (F350LP) camera. These 170-second exposures, processed with the Larson-Sekanina gradient filter, revealed a distinct double-jet structure that significantly evolved between the two December dates.
The Sunward Jet (Anti-tail): A prominent, long jet directed toward the Sun (an "anti-tail").
The Secondary Jet: A weaker jet appearing on the opposite side of the nucleus.
Temporal Variability: Between December 12 and December 27, the relative brightness and projected shape of these jets shifted noticeably. This "flickering" or change in geometry is a primary indicator of a rotational wobble.
2. The Mechanics of the "Wobble"
The "wobble" is technically a precessional motion. Research published in late 2025 (Serra-Ricart et al.) indicates that these jets are not perfectly aligned with the object's rotation axis.
| Feature | Data / Measurement |
| Rotation Period | Approximately 15.5 hours (refined from 16.8 hours). |
| Jet Wobble Cycle | Repeats every 7 hours and 45 minutes. |
| Jet Misalignment | The jet base is offset by roughly 8 degrees from the rotation pole. |
| Velocity | Estimated launch speeds exceeding 1 km/s near the nucleus. |
As the nucleus rotates, the jets sweep through space in a cone-like motion, similar to the beam of a slightly tilted lighthouse.
3. Scientific Implications: Comet or Probe?
The discovery of these jets has fueled a lively debate in the astronomical community, spearheaded by Harvard astrophysicist Avi Loeb.
The Natural Comet Hypothesis
Most astronomers view 3I/ATLAS as a "pristine" interstellar comet. The double jets are explained by:
Opposite Poles: Heat transfer through the nucleus could be activating "pockets" of volatile ices (like CO or $CO_2$) on both the day and night sides.
Composition: The presence of Nickel (Ni) without Iron (Fe) at large distances suggests a unique chemical fingerprint from its home star system, likely involving metal carbonyls that sublimate at low temperatures.
The Technological Hypothesis
Avi Loeb has proposed that the jets could be a signature of an artificial probe. His arguments include:
The Alignment Anomaly: The probability of the rotation axis being aligned within 8 degrees of the Sun by chance is roughly 0.5%.
Active Defense: In this view, the sunward jet could act as a shield against solar wind or radiation, while the secondary jet acts as a stabilizer or navigational thruster.
4. Why the "Anti-tail" is Rare
Typically, comet tails point away from the Sun due to solar radiation pressure. An anti-tail points toward the Sun. In the case of 3I/ATLAS, this is not just an optical illusion of perspective; it is a physical jet of larger dust particles or gas being ejected with enough force to resist the solar wind's push temporarily.
5. What’s Next for 3I/ATLAS?
3I/ATLAS made its closest approach to Earth on December 19, 2025, at a distance of 168 million miles. It is now speeding toward the outer solar system on a hyperbolic trajectory, meaning it will never return.
Future Observations: Astronomers are preparing for final high-resolution spectroscopic runs using the Keck Observatory and James Webb Space Telescope (JWST) to confirm the exact chemical composition of the "wobbling" gas.
The Legacy: 3I/ATLAS has provided the first-ever evidence of localized outgassing (jets) in an interstellar nucleus, offering a "time capsule" of a distant planetary system's birth.