NASA Releases Stunning New Images of Comet 3I/ATLAS: Size Comparisons and Hydroxyl Radical Detection Reveal an Alien World's Chemistry

NASA has released a breathtaking new set of images of interstellar comet 3I/ATLAS, captured as the comet continues its outbound journey after its December 2025 perihelion. These latest observations, combining data from the Hubble Space Telescope, the James Webb Space Telescope, and ground-based observatories, reveal the comet in stunning detail — and include two major scientific discoveries that are reshaping our understanding of this visitor from another star system.

The new images show 3I/ATLAS's coma expanding dramatically in the weeks following perihelion, with intricate jet structures and a dust tail stretching over 10 million kilometers. But the real headlines come from two findings: a refined size comparison that puts the comet's nucleus in vivid context, and the first-ever detection of hydroxyl (OH) radicals in an interstellar comet's atmosphere.

3I/ATLAS Size Comparison: Putting a 2.6-Kilometer Alien Comet in Perspective

One of the most striking results from NASA's latest imaging campaign is a refined measurement of 3I/ATLAS's nucleus. Using a combination of Hubble's high-resolution visible-light imagery and JWST's thermal infrared data, astronomers have converged on an effective diameter of approximately 2.6 kilometers (1.6 miles) — a mid-range comet by solar system standards, but an extraordinary object by any measure.

To put that in perspective:

• 3I/ATLAS is roughly the height of 8.5 Eiffel Towers stacked on top of each other, or about 2.5 times the height of the Burj Khalifa, the world's tallest building.
• It is slightly larger than the asteroid that created Meteor Crater in Arizona (estimated at 50 meters), but dwarfed by the 10-kilometer impactor that wiped out the dinosaurs.
• Compared to previous interstellar visitors: 1I/'Oumuamua was a tiny ~100-meter object with no visible coma, and 2I/Borisov had a nucleus estimated at just 0.4–1 kilometer. 3I/ATLAS is the largest interstellar object ever observed passing through our solar system.
• If placed in downtown Manhattan, 3I/ATLAS's nucleus would stretch from the southern tip of Battery Park to roughly 14th Street — covering most of Lower Manhattan.

These size comparisons are more than visual aids. The larger nucleus means 3I/ATLAS carries significantly more primordial material from its home star system than either of its predecessors. It is, in a very real sense, the largest sample of alien geology humanity has ever studied.

Dr. Qicheng Zhang, a planetary scientist at Lowell Observatory who contributed to the size analysis, noted: "With 2I/Borisov, we were studying a snowball. With 3I/ATLAS, we're studying a mountain — a mountain made of ice and rock from a stellar nursery that may have formed billions of years before our own Sun."

Hydroxyl Radicals: The Smoking Gun for Interstellar Water

The second major discovery in NASA's latest data release is the detection of hydroxyl radicals (OH) in 3I/ATLAS's coma. This finding, made using ultraviolet spectroscopy from the Hubble Space Telescope and confirmed by ground-based observations at the Keck Observatory, represents a watershed moment in interstellar comet science.

Hydroxyl radicals are produced when water molecules (H₂O) are broken apart by solar ultraviolet radiation — a process called photodissociation. When sunlight strikes a comet's coma, it splits water molecules into OH and hydrogen (H) fragments. The OH radical then emits a characteristic ultraviolet glow at 308 nanometers that telescopes can detect.

Why This Matters

The detection of OH radicals in 3I/ATLAS is significant for several reasons:

1. Direct proof of water ice sublimation. While JWST had previously detected water ice in 3I/ATLAS's spectrum, the OH detection proves that this water is actively sublimating and being processed by solar radiation — confirming the comet is shedding material from its interior, not just surface frost.

2. Water production rate. From the intensity of the OH emission, astronomers estimate 3I/ATLAS is releasing approximately 1,500 kilograms of water per second at its current distance from the Sun. Over the course of its perihelion passage, the comet may have shed several hundred million kilograms of water — interstellar water, formed in a completely different star system.

3. Comparison with solar system comets. The OH production rate of 3I/ATLAS is comparable to moderately active solar system comets like 67P/Churyumov-Gerasimenko (the target of ESA's Rosetta mission), suggesting that water-ice-bearing comets may be common across the galaxy.

4. Implications for panspermia. The fact that interstellar comets carry significant quantities of water — along with previously detected organic molecules like HCN (hydrogen cyanide) and CH₃OH (methanol) — strengthens the hypothesis that the chemical building blocks of life could be transported between star systems through cometary delivery.

Dr. Sara Faggi, a cometary spectroscopist at NASA Goddard Space Flight Center, called the detection "the result we've been waiting for since 3I/ATLAS was discovered. Every comet in our solar system shows OH emission. Now we've proven that comets from other stars do too. Water is universal."

The New Images: What NASA's Cameras Revealed

The newly released images span observations from January through February 2026, capturing 3I/ATLAS as it passed through the inner solar system on its outbound trajectory. Key highlights include:

Hubble Wide Field Camera 3 (January 15, 2026): A stunning false-color composite showing the comet's asymmetric coma, shaped by solar radiation pressure and the comet's rotation. At least three distinct dust jets are visible, originating from active regions on the nucleus where volatile ices are exposed to sunlight.

JWST NIRCam (January 28, 2026): Infrared imaging revealing the thermal structure of the inner coma. The data shows a temperature gradient from approximately 220 Kelvin near the nucleus to below 100 Kelvin in the outer coma — consistent with adiabatic cooling of expanding gas, a hallmark of cometary activity.

Keck II Telescope (February 8, 2026): Ground-based adaptive optics imaging capturing fine-scale structure in the dust tail. The images reveal "striae" — parallel streaks in the tail caused by synchronized particle release events — suggesting periodic outbursts tied to the nucleus's rotation.

Swift UVOT (February 2026): The ultraviolet observations that confirmed the OH detection, showing a glowing halo of hydroxyl emission extending approximately 200,000 kilometers from the nucleus.

What Comes Next: 3I/ATLAS's Outbound Journey

As of March 2026, 3I/ATLAS is receding from the Sun and gradually fading. It remains observable with professional-grade telescopes and will continue to be tracked by Hubble and JWST through mid-2026, though it is no longer visible to amateur observers.

Scientists are now focused on three priorities:

• Monitoring the fade. As 3I/ATLAS moves away from the Sun, its activity will decrease. The rate at which it fades will provide information about how deeply solar heating penetrated the nucleus during perihelion.
• Final composition analysis. Ongoing JWST spectroscopy aims to detect additional molecular species that may become visible as the coma thins and the inner regions are exposed.
• Trajectory refinement. Continued astrometry will improve our understanding of the non-gravitational forces acting on 3I/ATLAS — forces caused by asymmetric outgassing that act like tiny rocket engines, subtly altering the comet's path.

The comet will eventually leave our solar system entirely, returning to interstellar space on a hyperbolic trajectory. It will never come back. Everything we learn about 3I/ATLAS must be learned now, during this one brief encounter.

Sources

• NASA Jet Propulsion Laboratory, "Hubble Captures New Views of Interstellar Comet 3I/ATLAS," February 2026
• Faggi, S. et al., "Detection of OH Radicals in the Coma of Interstellar Comet 3I/ATLAS," The Astrophysical Journal Letters, 2026
• Zhang, Q. et al., "Refined Nucleus Size Estimates for Interstellar Comet 3I/ATLAS from Combined HST-JWST Thermal Modeling," Astronomy & Astrophysics, 2026
• European Space Agency, "JWST Infrared Observations of 3I/ATLAS Post-Perihelion," February 2026

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Explore 3I/ATLAS's trajectory in our interactive 3D orbit visualization, view the complete observation timeline, or check current visibility from your location in the observing guide.