Determining the dimensions of a comet from another star
The Hubble Space Telescope has captured the clearest image yet of an interstellar comet dubbed 3I/ATLAS. Early July 2025 saw the first discovery of this celestial guest, only the third known item of its kind.
It is on a hyperbolic route; therefore, it is simply going through our solar system before continuing its voyage into the immense emptiness of space.
NASA and European Space Agency astronomers are closely examining the item, which presents a rare chance to understand how planets develop in far-off areas of the Milky Way.
Hubble Offers a New Estimation of Size
With the help of the Hubble Space Telescope’s keen vision, experts could accurately determine the comet’s chilly core. Initially, its extent was thought to be many kilometers across.
The new data, however, imposed a tougher constraint on the nucleus. The diameter of the comet is thought to be between 320 meters and 5.6 kilometers.
Even with Hubble, the solid core, sometimes known as a snowball, is too small to be observed directly. Hence, these findings are a major advancement in our knowledge of the object’s characteristics.
Unraveling Comet Characteristics
Some enigmatic features have also come out in Hubble’s photographs. Ahead of the comet’s motion toward the Sun, a diffuse glow was seen instead of a normal trailing tail.
With one side of the comet remaining exposed to the Sun and constantly shedding dust, a sluggish rotation period is thought to be the source of this unusual phenomenon.
Another incongruous observation is that the spectrum of the comet reveals no evident gas emission from typical cometary molecules, which is not what would be anticipated from a comet having an active dust cloud.
Conflicting Hypotheses Regarding the Origin of the Object
Three I/ATLAS’s peculiar qualities have sparked a contentious argument among researchers. Harvard astronomer Avi Loeb has a different theory, even though most experts assert that the object is a natural comet with unusual properties.
Considering the brightness of the comet, he has proposed it could be a significantly bigger object and so an engineered extraterrestrial invention. Though it emphasizes the perplexing nature of the interstellar traveler, this theory differs from Hubble’s estimates of smaller sizes.
Future Observations from Additional Missions
3I/ATLAS is presently being studied by numerous observatories both on Earth and in space. For instance, the James Webb Space Telescope should provide fresh infrared information that might clarify the chemical composition of the object.
The comet is presently going 209,000 kilometers per hour, yet it presents no threat to Earth. It will pass near Mars before swinging around the Sun and finally entering interstellar space, never to be seen again.
Conclusion
The finding of the interstellar comet 3I/ATLAS has opened a new portal into the universe. Although Hubble has corrected its size estimate, its enigmatic properties have also ignited a fascinating scientific argument.
Hopefully, further observations from other missions will help to solve these riddles and advance our knowledge of the general cosmic surroundings.
You can watch an interview with Avi Loeb about his theory on the interstellar comet here. This video provides more insight into his controversial claims about the nature of 3I/ATLAS.
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