3I/ATLAS Update Today: Nucleus Detected, JWST Methane, and JUICE Data Incoming

The pace of discovery around interstellar comet 3I/ATLAS shows no sign of slowing. In the past two weeks alone, Hubble has directly detected the nucleus for the first time, JWST has identified methane — a molecule never before seen in an interstellar object — and SPHEREx has caught the comet in the act of a violent post-perihelion eruption. Meanwhile, ESA's JUICE spacecraft is preparing to downlink what may be the closest-ever observations of an interstellar body.

Here is everything that has happened as of February 9, 2026.

Hubble Detects the Nucleus: 1.3 km and Aspherical

The most significant structural result of the month comes from Man-To Hui and colleagues (arXiv: 2601.21569), who used Hubble Space Telescope data from July through November 2025 to directly detect the nucleus of 3I/ATLAS for the first time.

The team applied careful point-spread function (PSF) subtraction to isolate the nucleus signal from the surrounding coma. Their key findings:

• Effective radius: 1.3 ± 0.2 km — making it roughly twice the size of 2I/Borisov's nucleus (0.2-0.5 km) and comparable to many Jupiter-family comets in our own solar system.
• Aspherical shape with an axis ratio of at least 2:1, suggesting an elongated or bilobed nucleus — somewhat reminiscent of 67P/Churyumov-Gerasimenko, the comet visited by ESA's Rosetta mission.
• Geometric albedo of approximately 4.6% — consistent with a very dark, carbon-rich surface typical of cometary nuclei.

The nucleus size resolves months of speculation. Earlier estimates had ranged from 2 to 8 km based on indirect methods (non-gravitational accelerations, water production rates). The direct Hubble measurement settles the debate and places 3I/ATLAS firmly in the mid-range of known cometary nuclei.

The elongated shape is particularly interesting because it affects how outgassing torques spin up the nucleus — and may explain the dramatic rotation period change observed over the past months.

JWST Detects Methane: A First for Interstellar Objects

A team led by Sara Faggi (arXiv: 2601.22034) used the James Webb Space Telescope's MIRI instrument (Mid-Infrared Instrument) to obtain the first detection of methane (CH₄) in an interstellar object.

The observations, conducted in the 7-28 μm wavelength range, revealed:

• Methane (CH₄): Clearly detected in the mid-infrared, confirming the presence of this hydrocarbon ice in 3I/ATLAS's volatile inventory. This is the first time methane has been identified in any interstellar comet or asteroid.
• Carbon dioxide (CO₂): Strong emission features confirming CO₂ as one of the dominant volatiles, consistent with earlier SPHEREx and ground-based observations.
• Water (H₂O): Confirmed in the mid-infrared, complementing near-infrared detections.

The methane detection is significant because CH₄ is a hypervolatile — it sublimites at very low temperatures (~31 K), meaning it can only survive in cometary nuclei that have been stored in extremely cold environments for their entire history. Its presence in 3I/ATLAS tells us the comet's interior has remained essentially pristine since its formation in a distant protoplanetary disk, never having been significantly heated before entering our solar system.

The JWST data also allowed the team to measure production rate ratios between the volatiles, providing constraints on the temperature and chemical environment of 3I/ATLAS's birth system.

SPHEREx Catches a Post-Perihelion Eruption

NASA's SPHEREx infrared space telescope delivered one of the most dramatic results in its February 4 blog update: 3I/ATLAS was observed in December 2025 — two full months after its October 29 perihelion — "full-on erupting into space."

The infrared observations revealed:

• A sharp brightness increase compared to earlier observations, indicating freshly exposed volatile-rich material.
• Newly released water vapor, carbon dioxide, carbon monoxide, methanol, hydrogen cyanide, methane, and even rocky material streaming from the nucleus.
• Evidence of subsurface ices being exposed for the first time as the Sun's heat penetrated deeper into the nucleus through thermal conduction.

This delayed eruption is explained by thermal inertia — the insulating outer crust of the comet takes weeks to transmit solar heat to the volatile-rich interior. By December, the thermal wave had reached fresh ice deposits that had never been exposed to solar radiation, triggering the most intense outgassing event since perihelion.

The SPHEREx team noted that this "second peak" of activity is providing a unique window into the pristine interior composition of an interstellar comet — material that was last exposed to starlight in another planetary system billions of years ago.

TESS Time-Lapse: 28 Hours of Continuous Monitoring

Between January 15 and January 22, NASA's Transiting Exoplanet Survey Satellite (TESS) turned its wide-field cameras toward 3I/ATLAS, producing a continuous 28-hour time-lapse of the comet's motion and brightness variations.

The TESS observations revealed:

• Periodic brightness fluctuations with a 7.4-hour period, interpreted as the rotation of an elongated nucleus — consistent with Hui et al.'s finding of an aspherical shape with a 2:1 axis ratio.
• Short-lived outbursts — brief spikes in brightness lasting 20-40 minutes — appearing roughly every 15 hours, suggesting episodic exposure of fresh volatile pockets as the nucleus rotates.
• Evidence of a safe mode interruption partway through the observation, which cut short what was planned as a longer monitoring campaign.

The TESS data complements the Hubble nucleus detection by providing an independent constraint on the rotation period and confirming the elongated geometry from a completely different observational approach (photometric light curve vs. direct imaging).

The Spinning Top: From 16 Hours to 7

One of the most dramatic changes in 3I/ATLAS since perihelion is its rotation period. Pre-perihelion ground-based observations in July 2025 measured a leisurely rotation of 16.16 hours. By late January 2026, Hubble photometry and the TESS light curve both indicate a period of approximately 7.1 hours — the nucleus has more than doubled its spin rate.

This dramatic spin-up is caused by outgassing torques. As asymmetric jets of gas and dust erupt from the nucleus, they act like tiny rocket engines, applying angular momentum. For 3I/ATLAS, the intense perihelion activity overwhelmingly accelerated the rotation.

The post-perihelion jet structure visible in Hubble images reflects this rapid spin: three symmetric mini-jets separated by approximately 120 degrees wobble back and forth by ±20 degrees with a period matching the 7.1-hour rotation. The rotation axis is nearly aligned with the Sun-comet direction (within ~20 degrees), creating a cone-like sweep pattern.

Whether the nucleus continues to spin up or begins to slow down as outgassing weakens is an open question. Extreme spin-up can threaten structural integrity — if the centrifugal stress exceeds the tensile strength of the nucleus, it could fragment. This is being closely monitored.

JUICE Data Incoming: February 18-20

Perhaps the most anticipated near-term event is the expected downlink of ESA's JUICE spacecraft data between February 18 and 20, 2026.

JUICE (JUpiter ICy moons Explorer), launched in April 2023 and currently en route to Jupiter, passed within observational range of 3I/ATLAS during its gravity assist trajectory. The spacecraft's suite of instruments — including cameras, spectrometers, and particle detectors — may have captured data on the comet from a distance and geometry impossible for Earth-based telescopes.

If successful, the JUICE observations would represent the closest-ever encounter between a spacecraft and an interstellar object. While no dedicated flyby was possible (JUICE's trajectory is fixed for its Jupiter mission), even opportunistic data from the spacecraft's instruments could provide:

• UV spectroscopy of the coma from an angle complementary to Hubble's view
• Particle measurements of dust and gas encountered along JUICE's trajectory
• Images from a perspective unavailable from Earth

The science team is expected to begin releasing preliminary results shortly after the data downlink completes.

Water Production Asymmetry: The Thermal Lag Story

SOHO/SWAN Lyman-alpha observations have precisely quantified a remarkable asymmetry in water production around perihelion:

• Inbound (approaching perihelion): Water production increased as the inverse 5.9 power of heliocentric distance — an extremely steep ramp-up as fresh surface ices sublimated rapidly.
• Outbound (receding from perihelion): Water production declined as only the inverse 3.3 power — a much gentler falloff, meaning the comet stayed active far longer than a simple solar-heating model would predict.

Peak water production reached approximately 3.17 × 10²⁹ molecules per second on November 6, 2025 — about one week after perihelion. This delay between closest solar approach and peak outgassing is direct evidence of thermal inertia: the nucleus takes time to heat through, and its deepest volatile-rich layers continue outgassing well after the solar flux has peaked.

The asymmetry ratio (5.9 inbound vs. 3.3 outbound) is more extreme than most solar system comets, possibly because 3I/ATLAS's interior ices were encountering solar heat for the first time ever — providing an unusually large reservoir of pristine volatile material to drive extended outgassing.

By February 2026, at approximately 3.5 AU from the Sun, water-ice sublimation has largely ceased. But CO₂ and CO — which sublimate at much lower temperatures — may continue driving residual activity.

The Loeb Controversy: Panspermia Claims and Pushback

Harvard astronomer Avi Loeb has continued to make headlines with increasingly bold claims about 3I/ATLAS.

In early February, Loeb published an essay titled "Is There Life on 3I/ATLAS?", arguing that the comet's rich volatile inventory — particularly the detection of prebiotic molecules like hydrogen cyanide (HCN) and methanol — raises the possibility that interstellar comets could serve as vehicles for panspermia, the hypothesis that life can be transferred between star systems via natural means.

Loeb has also estimated that approximately 10 trillion interstellar objects like 3I/ATLAS may be passing through the solar system at any given time — most too small or dark to detect with current surveys. He argues this creates a "cosmic conveyor belt" capable of distributing organic molecules, and potentially microbial life, across the galaxy.

The broader astronomical community has responded with measured skepticism:

• Jason Wright (Penn State) and other SETI researchers have systematically rebutted suggestions that 3I/ATLAS shows any artificial or anomalous characteristics. Every observation to date — chemical composition, outgassing behavior, trajectory, nucleus properties — is consistent with a natural cometary body.
• The four-telescope SETI search (Allen Telescope Array, Parkes/Murriyang, MeerKAT, Green Bank) found zero technosignatures down to 0.1 watts EIRP — the sensitivity of a cell phone.
• While the detection of prebiotic molecules is genuinely significant for understanding the chemical building blocks available for planetary formation across the galaxy, the leap from "HCN exists in a comet" to "life could be transferred between star systems" remains speculative and untestable with current data.

The controversy underscores a broader tension in 3I/ATLAS coverage: the comet's genuine scientific significance is extraordinary enough without embellishment.

What's Next

The next five weeks are packed with pivotal events:

• February 18-20: ESA JUICE spacecraft data downlink — potentially the closest observations of an interstellar object ever made by a spacecraft.
• March 16: Jupiter closest approach at 0.358 AU (53.5 million km). Jupiter's tidal field may trigger fresh outbursts. NASA's Juno spacecraft, still operational in Jovian orbit, may attempt imaging.
• Ongoing: Hubble, JWST, and ground-based telescopes continue monitoring as 3I/ATLAS fades through magnitude 17+. Every photon collected adds to the most complete portrait ever assembled of an object born around another star.

The comet currently sits in the constellation Gemini, approximately 3.5 AU from the Sun, fading through magnitude 16-17. It remains accessible to CCD-equipped telescopes of 10 inches or larger under dark skies, though visual detection is no longer possible.

As 3I/ATLAS approaches Jupiter, the question is whether the gas giant's immense gravity will squeeze one last burst of activity from this interstellar visitor before it begins the long, silent coast into the outer solar system and beyond.

Track 3I/ATLAS in real time on our Orbit page, check observing conditions on the Observing page, and explore the full timeline of discoveries.