NASA and the European Space Agency’s Hubble Space Telescope has obtained the sharpest image to date of interstellar comet 3I/Atlas, the third known visitor from outside our solar system (following ‘Oumuamua and comet 21/Borisov), discovered in early July. This observation enabled a more precise estimate of the size of its icy nucleus, now believed to range between 320 meters and 5.6 kilometers in diameter. The findings, detailed in a study pending publication in The Astrophysical Journal Letters and currently available on arXiv, reveal that while Hubble’s images impose tighter constraints on the nucleus size than prior ground-based estimates, the comet’s solid core remains obscured from direct view. Future observations with instruments like the James Webb Space Telescope will refine understanding of this unique celestial body, including its chemical composition. Hubble’s image clearly shows a dust plume ejected from the sun-warmed side of the comet and the beginnings of a dust tail extending away from the nucleus. Data indicates a dust loss rate consistent with comets first detected at approximately 480 million kilometers from the Sun—behavior remarkably similar to solar-bound comets originating within our own system. The critical distinction is that this interstellar visitor formed in another solar system, within a different region of the Milky Way. Traveling at approximately 210,000 kilometers per hour—the highest speed ever recorded for a solar system interloper—3I/Atlas provides compelling evidence of its billions-of-years journey through interstellar space, gaining momentum from gravitational slingshot effects caused by countless stars and nebulae encountered along its path.
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