NASA’s TESS and Hubble Capture Best Look Yet at Interstellar Comet 3I/ATLAS

On a January night when Earth lined up almost perfectly between the Sun and a frozen wanderer from another star, two of NASA’s flagship space observatories were watching.

High above the planet, the Transiting Exoplanet Survey Satellite, or TESS, tracked a faint point of light as it glided across its camera. Farther out, the Hubble Space Telescope snapped high‑resolution images of a gauzy tail and hidden jets, backlit by the Sun.

Their shared target was 3I/ATLAS, the third confirmed interstellar object ever observed and the first interstellar comet to be studied in comparable detail to those born in our own solar system.

A January campaign—a week of continuous TESS monitoring from Jan. 15 to 22, capped by a carefully timed Hubble imaging run on Jan. 22—has turned 3I/ATLAS from a dim, fast‑moving dot into the best‑characterized interstellar comet to date. Scientists say the data will help reveal how another planetary system builds comets, and how ready Earth’s observatories are for future visitors from deep space.

A visitor from another star

3I/ATLAS, also known as C/2025 N1 (ATLAS), was discovered July 1, 2025, by the Asteroid Terrestrial‑impact Last Alert System in Chile. Its orbit is clearly hyperbolic, meaning it is not bound to the Sun and must have originated around another star.

The comet passed closest to the Sun in late October 2025, skimming inside the orbit of Mars at about 1.4 astronomical units. It made its nearest approach to Earth on Dec. 19, 2025, at roughly 1.8 astronomical units—about 170 million miles.

NASA has stressed that 3I/ATLAS poses no danger. “The comet poses no threat to Earth and will remain far away,” the agency said in an online overview of the object.

What makes the comet unusual is not its trajectory past Earth, but what that trajectory allows astronomers to see. Unlike 1I/ʻOumuamua, which showed no detectable gas or dust, 3I/ATLAS is an active comet with a visible coma and tail. Unlike 2I/Borisov, it passed through a near‑perfect opposition in January, when the Sun, Earth and comet lined up to put the dust directly backlit from our point of view.

That alignment on Jan. 22, when the angle between the Sun, Earth and comet shrank to about 0.7 degrees, gave Hubble a rare chance to study how light scatters from dust grains from another star system.

An exoplanet hunter changes jobs

TESS was not built to study comets. Launched in 2018, the spacecraft stares at large patches of sky for weeks at a time, measuring the brightness of hundreds of thousands of stars to catch the tiny dips caused by planets passing in front of them.

But the same design—wide‑field, high‑cadence, uninterrupted imaging—makes TESS a powerful tool for tracking how small bodies change brightness over hours and days.

In January, NASA paused TESS’s regular observing plan to run a special campaign on 3I/ATLAS. From Jan. 15 to 22, during an internal segment labeled Sector 1751, mission controllers pointed the satellite so that the comet would stay on a single detector, known as Camera 2, CCD 3.

TESS collected full‑frame images of the field and high‑cadence “target pixel” cutouts along the comet’s predicted path. Those data, released publicly Jan. 27, show 3I/ATLAS as a moving point with a faint tail drifting through a dense star field.

“In the TESS data, 3I/ATLAS appears as a bright dot with a tail passing through a field of stars,” NASA wrote in a Jan. 27 blog post announcing the campaign. The comet’s brightness during the sequence was about magnitude 11.5, roughly 100 times fainter than the limit of naked‑eye visibility.

A solar panel issue briefly pushed TESS into safe mode early in the run, creating a gap between Jan. 15 and 18. Even so, the mission captured about 28 hours of continuous coverage spread over the week.

That nearly unbroken light curve is intended to pin down the comet’s rotation and search for subtle flares.

“Continuous photometry from space fills in the gaps you just can’t avoid from the ground,” said one TESS scientist in a NASA question‑and‑answer post about the observations. “If the comet has short‑lived outbursts or a rotation period close to a day, you really want that space‑based perspective.”

Early analyses combining ground‑based data and Hubble images have suggested a rotation period of roughly 7 hours for 3I/ATLAS. Teams are now using the TESS light curve to refine that estimate and test whether the comet’s spin state is stable or slowly changing as jets of gas act like tiny thrusters.

Hubble’s backlit close‑up

While TESS watched the comet’s overall brightness, Hubble focused on structure.

On Jan. 22, around the moment of opposition, Hubble’s Wide Field Camera 3 took a series of images of 3I/ATLAS using a broad optical filter. Raw frames showed a roughly symmetrical coma, but after image processing to suppress the general glow, a more complex pattern emerged.

The processed views revealed a prominent, narrow dust feature known as an anti‑tail, pointing roughly toward the Sun and Earth, and three additional, smaller jets arranged around the nucleus.

The anti‑tail appears to be a sheet of dust particles lying close to the comet’s orbital plane, made particularly conspicuous because of the geometry. With the Sun behind Earth, the dust is seen almost exactly along its length, like a thin beam pointing at the planet.

“Hubble’s near‑opposition images show a striking anti‑tail and multiple mini‑jets, indicating a nucleus with several active regions,” Man‑To Hui of the Shanghai Astronomical Observatory, who led the Hubble analysis, said in a recent preprint describing the observations.

Using careful modeling to separate the nucleus from the surrounding coma, Hui’s team estimated that the comet’s solid core has an effective radius of about 1.3 kilometers (about 0.8 miles). That is small by the standards of some long‑period comets, but typical for an icy body that has spent eons in deep space.

The team also measured a modest opposition surge—a brightening of about 0.2 magnitude as the phase angle approached zero—consistent with how dust in many solar‑system comets reflects light under similar conditions. The rate at which the comet’s activity has declined since its closest approach to the Sun also matches patterns seen in local comets.

A familiar kind of alien

Those findings fit with a broader picture emerging from radio, infrared and optical observations around the world. Telescopes have detected standard cometary gases such as water products and hydrogen cyanide in 3I/ATLAS’s coma. Radio astronomers reported the first detection of natural radio emission from an interstellar comet, in the form of hydroxyl lines produced as sunlight breaks apart water molecules.

A separate team, led by Thomas Marshall Eubanks of Space Initiatives, used precise position measurements from spacecraft including NASA’s Psyche mission and the European Space Agency’s Trace Gas Orbiter at Mars to study tiny deviations in the comet’s motion. They concluded that the non‑gravitational accelerations seen in 3I/ATLAS can be explained by conventional outgassing.

“3I/ATLAS is exotic and wonderful. It is also a comet,” Eubanks said in a December interview about the work.

Not all researchers agree that the case is closed. Harvard astrophysicist Avi Loeb has argued that some aspects of the comet’s behavior, including the configuration of its jets and its acceleration, deserve closer scrutiny and could, in principle, point to non‑natural explanations. His claims have drawn attention in popular media, but have not been widely accepted in peer‑reviewed studies.

Requests for internal documents on 3I/ATLAS have also reached outside the scientific community. When a prominent records requester sought information from the Central Intelligence Agency about the comet, the agency replied that it could “neither confirm nor deny” the existence of responsive records—a so‑called Glomar response typically used to protect intelligence sources and methods. The CIA did not elaborate on the reason for its reply.

At the same time, major observatories, including TESS and Hubble, have made their data public through standard archives, allowing independent teams to scrutinize the comet.

A dress rehearsal for the next visitor

For planetary scientists, 3I/ATLAS is as much about practice as it is about discovery.

The object will pass closest to Jupiter in March before fading into the outer solar system, eventually heading back into interstellar space. Along the way, it is serving as a test of an increasingly distributed observing network: all‑sky surveys on Earth, multi‑purpose spacecraft in orbit around Mars and elsewhere, and space telescopes originally built for other tasks.

The January campaign showed that missions such as TESS and Hubble can pivot on relatively short notice to catch a one‑time event, and that coordinated scheduling can extract complementary measurements—time‑resolved brightness and high‑resolution structure—from the same fleeting visitor.

Future interstellar objects may arrive with less warning or on more threatening paths. Astronomers are already developing concepts for rapid‑response spacecraft that could intercept such bodies for close study, and pointing to 3I/ATLAS as evidence that the scientific payoff can be high.

For now, the comet that came from another star is shrinking to invisibility in backyard telescopes. On computer servers on and above Earth, however, its detailed record remains: hours of flickering light curves, frames of jets and dust, and spectra of ices that formed in a different sun’s long‑gone nursery.

Together, those data mark a quiet milestone. For the first time, an interstellar comet has been studied with the same depth and tools routinely applied to local comets, turning an anonymous wanderer into a well‑described object with a measured size, spin and structure—and a place in a growing catalog of visitors from beyond the Sun.