Press Enter or click to view the image in full sizeOn July 21, 2025, the Hubble Space Telescope at 3i/Atlas showed sunlight rays in front of objects, and the tail often observed in comets has no tail. (Image source: D. Jewitt et al./NASA/Wikimedia)
The best image we have so far with the Nova Object 3i/Atlas is Hubble Space Telescope On July 21, 2025. The image shows the coma rays before the 3i/Atlas moves toward the sun. There is no evidence of a bright comet tail in the opposite direction. This ray is interpreted as the evaporation of dust facing the sun from 3i/Atlas.
Figure 3 of the analysis paper (accessible here) shows a steep surface brightness curve of gloss with a projected power law slope of -3, meaning a three-dimensional emissivity with a radial power law slope of -4. Such slopes are steeper than those observed in comets in solar system. Together with my amazing colleague Eric Keto, we realized that the slope of -4 is consistent with the alternative model where dust flows out around the central source around the 3i/Atlas. This model naturally illustrates the steep brightness curve, as the slope of the outflow density of -2 is accompanied by the radial drop in the illumination radiation flux, with an additional drop of -2.
Press Enter or click to view the image in full sizeSurface brightness is a function of the angular distance from the 3i/Atlas core Hubble Space Telescope image. Average the brightness by a 0.8 arc-wide strip along the axis connecting 3i/Atlas. (Picture: D. Figure 3 of Jewitt et al. 2025)
If the 3i/Atlas produces its own light, it may be much smaller than what the model reflects sunlight expects. The reflection model has a diameter of up to 20 km, which is untenable, as a limited reservoir of rock material in interstellar space can only provide such huge rocks every 10,000 years or more (see calculations in my paper).
Last night, we held the annual Football Cup among students at the Harvard Institute for Theory and Computing, where I served as director. Although I scored 2 goals for the teacher team, the students won 3 to 2. Disappointed with the results, but woke up the next morning and I focused on 3i/Atlas.
Press Enter or click to view the image in full sizeImages of Harvard School of Theory and Computing Students vs. College of the Year Soccer Games (Credit: TJ Martin, August 16, 2025).
First, I calculated that the luminosity of 3i/Atlas needs to be 10 GW. Second, I realized that the steep brightness curve surrounding the 3i/Atlas means that the core dominated the observed light. Regardless of the origin of light, it must be persisted. In other words, the nucleus predominates the emission of light surrounding it.
The illumination of sunlight cannot explain the steep 1/r⁴ profile of scattered light, where r is the radial distance from the nucleus. This is because the steady dust outflow forms a 1/r² profile that disperses sunlight in the same emissivity profile. Sunlight will dominate lighting in this model, as the rock core reflects only a small portion of the sun's intensity than in the area. Hubble Space Telescope image. Another possibility for the steep brightness profile is that the scattered aura is made of ice-cold particles that evaporate when moving from the 3i/Atlas toward the sun. This could explain why these scattering particles have no tails. The required evaporation time must be 10 minutes, but it is not clear whether this will result in the observed 1/R⁴ brightness profile.
The simplest explanation is that the 3i/Atlas core produces most of the light. What I calculated is that the core cannot be a heat emitter with an effective surface temperature below 1000 degrees Kelvin, or its peak emission wavelength will exceed 3 microns, exponential cutoff at shorter wavelengths, incompatible with the data. At higher effective temperatures, the required luminosity required for the 3i/ata can be obtained from a source diameter of less than 100 meters. The compact bright emitter will make the size of the 3i/map atlas comparable to the previous interstellar objects 1i/`oumuamua or 2i/borisov, making more sense than the 20 km size inferred in a model reflecting sunlight than the 20 km size.
What can make up the required light source?
I first calculated that a primitive black hole with an eagle temperature of 1,000 degrees can only produce 20 nmwatts of power, which is obviously not enough to power 3i/Atlas. Natural nuclear sources may be rare fragments of nearby supernova cores, with abundant radioactive materials. Given the scarcity of radioactive elements in interstellar space, this possibility is extremely unlikely.
Additionally, the 3i/Atlas may be a spacecraft powered by nuclear energy, and the dust emitted from the frontal surface of its lobe may come from dirt that accumulates on its surface during interstellar travel. This cannot be ruled out, but better evidence is needed to be feasible.
To insist that 3i/Atlas are natural objects, one may consider the hypothetical situation of objects that are frictionally heated on an environmental medium. In this case, the momentum flux of dust flowing out of the object must exceed the momentum flux of the ambient medium of the remaining frame of the object, the so-called ambient RAM pressure. Otherwise, the ambient medium will inhibit the outflow of dust. What's going on in this situation?
Given the mass loss rate (6-60 kg per second) and the ejection speed of dust (20-2 km per second) Hubble Space Telescope Images, I calculated a slight exclusion of this model. In addition, the required ambient density is ordering magnitude greater than the mass density of the twelve gases and dust, and the mass density of the three-generation gases and dust passes through this mass density when the 3i/Atlas passes through the main asteroid belt.
This leads us to interpret the brightness profile near the 3i/Atlas as originating from a central light source. Its potential technical sources are supported by fine-tuning trajectories (visualized here and discussed here).
The new interstellar object 3i/attalog is expected to be 28.96 (+/- 0.06) million kilometers from Mars on October 3, 2025. This will provide an excellent opportunity to observe 3i/Atlas at Hirise Camers near Mars, the Hirise Camera near Mars, one of six instruments on a Mars reconnaissance plane. This morning, I encouraged the Hirise team to use the camera in the first week of October 2025 to collect new data on 3i/Atlas. They responded favorably. Observe the 3i/Atlas of 3i/Atlas at about the same time, as the 3i/Atlas in our sky is close to the direction of the sun. The more data we collect on 3i/Atlas, the closer we will be to understanding its essence.
About the Author
Press Enter or click to view the image in full size(Photo source: Chris Michel, National Academy of Sciences, 2023)
Avi Loeb He is the founding director of Harvard University's Galileo Project – Black Hole Initiative, Director of the Institute of Theory and Computing at the Center for Astrophysics at Harvard University, and former Chairman of the Department of Astronomy at Harvard University (2011-2020). He was a member of the President's Advisory Committee on Science and Technology and was also the Chairman of the National Academy's Physics and Astronomy Committee. He isalien: The first sign of smart life outside the earth“and textbook co-author”Life in the universe”, both published in 2021. The paperback version of his new book is titled “Interstellar”, published in August 2024.