Astronomers reveal comet 3I/ATLAS is much larger than expected

The discovery of comet 3I/ATLAS has captivated astronomers since its detection in July 2025, originating from interstellar space. It is noteworthy for being the third recorded interstellar object to enter the inner solar system, following 'Oumuamua' in 2017 and comet '21/Borisov' in 2019. This comet, which was identified using data from the Asteroid Terrestrial-impact Last Alert System, a NASA-funded project located in Chile, has been reported to be significantly larger than scientists initially anticipated. Harvard astrophysicist Avi Loeb observed that the comet likely weighs more than 33 billion tons by analyzing its trajectory and mass loss rate, using data collected by the Webb Space Telescope on August 6, 2025. He estimated the diameter of its nucleus to be over 3.1 miles, making 3I/ATLAS the largest interstellar object recorded to date. Composed primarily of carbon dioxide and water ice, the comet's coma, or gaseous atmosphere, has shown a considerable abundance of carbon dioxide gas. Despite its impressive size and unusual trajectory, astronomers confirmed that 3I/ATLAS poses no threat to Earth. However, it is expected to come relatively close to other planets, including a proximity of 1.67 million miles to Mars' orbit on October 3, 2025, which is notable for such cosmic travelers. Following its close encounters, the comet will pass too near the sun to remain visible, but it is projected to reappear in early December 2025 after traveling beyond the sun's obscuring glare. The comet's trajectory has been of special interest to researchers who are keenly observing its path as it travels through the solar system.