Astronomers are closely tracking the interstellar comet known as 3I/ATLAS as it prepares for its nearest approach to Earth, expected on Friday. First identified earlier this year, the object has already marked several significant milestones during its journey through the solar system. The comet was initially spotted on 1 July by the ATLAS survey telescope in Rio Hurtado, Chile, when it was around 420 million miles from Earth, according to NASA. Travelling at exceptional speed on an unusual trajectory, it has been classified as an interstellar visitor — only the third such object ever confirmed passing through our solar system from beyond.
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Although the discovery was formally announced in July, astronomers later traced earlier sightings back to mid-June. Archived data from multiple ATLAS telescopes worldwide, along with observations from the Zwicky Transient Facility in California, helped confirm its origin and path.
By 21 July, scientists were able to assess the comet’s physical characteristics using the Hubble Space Telescope, which captured the sharpest images obtained so far. These observations suggest the comet’s nucleus could be up to 3.5 miles across, though it may be significantly smaller.
Further analysis followed in August, when NASA’s James Webb Space Telescope examined the comet using its near-infrared instruments to study its structure and chemical composition. Shortly afterwards, the SPHEREx mission monitored the object for over a week, gathering additional data and releasing new imagery. In early September, NASA’s Psyche spacecraft observed the comet for several hours from a distance of roughly 33 million miles. Its multispectral imaging allowed scientists to refine calculations of the comet’s trajectory by tracking reflected sunlight from its surface and faint surrounding coma.
Additional monitoring was carried out by NASA’s STEREO mission, which usually studies solar activity. Researchers noted that the comet appears to take on a bluish hue as it moves closer to the Sun, a feature of particular scientific interest.
Experts say the comet’s closest approach to Earth will offer the clearest opportunity yet to study its features. Darryl Z. Seligman, an assistant professor of physics and astronomy at Michigan State University, said this phase would make key characteristics easier to detect with ground-based and space telescopes.
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Scientists believe 3I/ATLAS could provide valuable insights into how planetary systems form. Its apparent differences from comets native to our solar system may help researchers better understand the materials and processes that shaped our cosmic neighbourhood billions of years ago.
