Below is a short summary and detailed review of this video written by FutureFactual:
Comet 3I Atlas Update: Interstellar Visitor Nears Perihelion with New Insights from Hubble JWST and TESS
Short summary
Comet 3I Atlas, the first interstellar object to visit our solar system in years, continues to reveal surprising details as it approaches perihelion on October 30. Data from Hubble, JWST and TESS show a smaller nucleus than early estimates, a complex coma with varying outgassing patterns, and a carbon chain depletion signature. Ground-based imaging documents a growing tail and detectable cyanide emission, while polarization measurements indicate unique light scattering. Amateur observations have even suggested a green hue under specific lighting, though verification is ongoing. The video reviews discoveries since July, including brightness surges, possible rotation hints, and the outlook for future observations before Atlas disappears behind the Sun.
Introduction and context
A new era of interstellar reconnaissance is unfolding as Comet 3I Atlas continues to be observed by multiple major facilities. Identified as the third interstellar object to visit our solar system, Atlas travels at roughly 58 kilometers per second and carries an estimated age between 3 and 11 billion years. Since the initial July coverage, the body has become a focal point for researchers, leading to a rapid increase in published studies from a handful to dozens within weeks.
Key observational breakthroughs
Hubble captured Atlas on July 21 at 446 million kilometers from Earth, revealing a teardrop-shaped dust coma and providing a refined nucleus size estimate of 440 meters to 5.6 kilometers in diameter. The dust coma majority now accounts for much of the reflectance, revising earlier nucleus-only interpretations. JWST's near infrared spectroscopy exposed a complex coma morphology with outgassing patterns sensitive to the elements present. Early indications showed carbon monoxide and carbon dioxide sublimation dominating over water at this stage, with substantial dust emission directed toward the Sun, likely from dust grain fragmentation and gas-sustained lifting. TESS data, including pre-discovery imaging, helped verify early brightness trends and highlighted a larger-than-expected brightening as Atlas approached Earth.
Physical properties and composition
Ground-based efforts, including TRAPPIST North and South, and Gemini South, contributed to a refined understanding of Atlas's activity. Observations indicate the comet's CN (cyanide) emission is strengthening, with measurements suggesting the object released about 800 sextillion CN molecules per second when near 3 astronomical units from the Sun. Relative to other comets, Atlas shows significant carbon-chain depletion: the ratio of C2 to CN is less than 0.09, making it one of the most carbon-chain-depleted comets observed. This attribute, shared with Borisov, may reflect the primordial conditions under which Atlas formed, though the small interstellar sample size cautions against broad generalizations. The potential for increased C2 production, or the emergence of other volatiles like water as Atlas nears perihelion, remains a key area of interest for ongoing monitoring.
Outgassing, rotation, and tail development
Despite initial uncertainties, several studies converge on a rotation period near 16 hours, with hints of a longer 29-hour signal in noisier data. Imaging from Gemini shows a tail extending about 1/120 of a degree, larger than earlier July observations, suggesting rising activity as the Sun warms the coma. The presence of CN in the coma, and potential indicators of diatomic carbon fluorescence, point to evolving chemistry as Atlas moves deeper into the inner solar system. Researchers also note that dust production can complicate the appearance and apparent tail length, due to the Sun-driven radiation and drag on dust grains.
Polarization and unusual scattering
Polarimetric measurements mark Atlas as having an exceptionally deep and narrow negative polarization branch, a scattering behavior not previously observed for interstellar objects or known comets. This implies distinctive dust properties or surface regolith structure, potentially placing Atlas in a distinct small-body class and inviting comparisons with some outer solar system bodies such as certain trans-Neptunian objects. The finding underscores how polarization can reveal physical properties not accessible through spectroscopy alone.
Green hue observations and amateur interest
During a recent lunar eclipse, observers reported a green hue on Atlas, which would align with C2 fluorescence under sunlight. Given Atlas’s carbon-chain depletion, confirmation is pending and researchers caution against premature interpretation. Nonetheless, amateur observations highlight the broader public engagement and the importance of citizen science in contributing to early signal recognition during dynamic apparitions.
Origin discussions and scientific caution
The discourse around Atlas’s origin has featured Avi Loeb proposing that Atlas may be too large to be a typical asteroid and speculating about alien technology. Critics emphasize that early data, including comets’ coma and nucleus estimates, are still evolving and that more defensible explanations lie in natural dynamics. Subsequent analyses challenge non-gravitational acceleration scenarios and argue that current trajectory data are consistent with standard gravitational and outgassing forces. This debate illustrates the importance of data credibility and the dangers of premature conclusions while maintaining healthy scientific skepticism about extraordinary claims.
Perihelion and future observations
Atlas is scheduled to reach perihelion on October 30 at about 1.4 astronomical units from the Sun. It will be unobservable close to the Sun but is expected to reemerge in December for renewed study. Observatories likely to contribute include NASA's SOHO, Sphere X, Maven, as well as ongoing work from Hubble, James Webb, and Gemini. The coming weeks will be pivotal for understanding how Atlas responds to solar heating, whether it breaks apart, and how its activity evolves as it traverses the inner solar system. In the broader sense, Atlas continues to drive inquiry into interstellar object populations and the processes that shape their physical and chemical makeup.
Closing perspective
The video emphasizes the pattern-seeking approach essential to space science: accumulate multi-instrument data, identify consistent signals, and test hypotheses against evolving evidence. It also highlights the value of collaboration across space- and ground-based facilities to capture the dynamic behavior of a rare interstellar visitor, while acknowledging the inherent uncertainties of a rapidly developing dataset. As Atlas fades behind the Sun and science advances, researchers remain poised to extract new insights from every observation and to refine our understanding of how interstellar objects fit into the broader picture of our cosmic neighborhood.