Everyone's favorite comet is about to fly away from Earth and continue its interstellar journey.
3I/ATLAS recently flew past Earth on Friday, December 19, giving astronomers a fleeting but invaluable chance to study the material created around another star. Now, after the next collision, the guest is already returning to deep space, taking his secrets with him, but leaving behind a lot of data that scientists will study for years.
3I/ATLAS approaches Earth
On December 19, the interstellar invader made its closest approach to Earth, coming within 168 million miles of our planet around 1 a.m. EST. 3I/ATLAS had already passed its closest point to the Sun, and this flyby marked the beginning of its exit from the inner Solar System.
From here, the comet will continue to move outward, brushing past planets before eventually leaving the solar system entirely and resuming its long journey through the Milky Way.
First discovered on July 1, 2025 by NASA's Asteroid Impact Late Warning System, 3I/ATLAS immediately stood out. Its trajectory showed that it did not originate anywhere near the Sun, making it only the third known object found passing through our solar system from space. interstellar space. Researchers traced it to a region of the galaxy older than our 6.4 billion-year-old solar system, meaning 3I/ATLAS formed around a star that predated the Sun itself.
But you don't have to say goodbye just yet. Skywatchers hoping to catch one last look can tune in to the Virtual Telescope Project's livestream starting at 11:00 pm EST as 3I/ATLAS slowly fades from view.
Read more: New images of comet 3I/ATLAS show how magical the Universe could be
What Scientists Have Learned and Still Hope to Find Out
When 3I/ATLAS was first discovered, speculation quickly spread, including claims that it could be an alien spacecraft or probe. Careful observations soon disproved these ideas. Months later, astronomers confirmed that 3I/ATLAS looked strikingly familiar to comets in our solar system: Its icy core was surrounded by a glowing coma of gas and dust that changed chemical states as the comet warmed.
3I/ATLAS also provided researchers with a rare opportunity to study raw ingredients which form comets, asteroids and planets around stars other than the Sun. Observations at different wavelengths revealed a composition rich in carbon, oxygen and nitrogen—elements also common in comets in our solar system.
One particularly intriguing question concerned X-rays. Although comets in our solar system emit X-rays, astronomers have not confirmed whether interstellar comets behave in the same way. Using Japan's X-ray Imaging and Spectroscopy Mission, scientists observed 3I/ATLAS in late November 2025, detecting X-rays extending nearly 248,000 miles from its core.
Data collected during 3I/ATLAS's latest close approach to Earth will help determine how these emissions form and whether they reflect processes observed closer to home.
Why have comets always fascinated humanity?
Long before telescopes and space missions, comets inspired awe, fear and fascination. Humans have likely been fascinated by comets for longer than any archaeological record can attest. Ancient cave paintings resembling comets are appearing in Scotland and Italy, and Chinese astronomers have carefully tracked them for centuries, believing they reveal the “will of heaven,” according to the European Space Agency.
Elsewhere, comets were often considered an omen. Roman astrologers blamed them for a variety of disasters, from wars to disease, and medieval fear is famously preserved in the depiction of Halley's Comet in the Bayeux Tapestry.
Even as recently as 1910, the discovery of cyanogen in the tail of Halley's Comet caused mass panic, complete with gas masks, prayer vigils, and so-called comet defense pills.
Although 3I/ATLAS' As the visit draws to a close, its discoveries will continue to shape our understanding of worlds far beyond our own.
Read more: Another comet, ATLAS, appears to be fragmented after its close approach to the Sun.
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