The third interstellar object ever detected has made its nearest approach to our planet, providing a rare opportunity for a “solar system-wide” observation campaign involving telescopes from Earth to Mars.
The rare interstellar comet 3I/ATLAS reached its closest point to Earth on Friday (19 December), passing safely at a distance of 270 million kilometers (1.8 AU). Traveling on a hyperbolic path that will eventually take it out of our solar system forever, the icy visitor has become the focus of intense study by NASA and the European Space Agency, who’ve used the encounter to look into the chemical makeup of a body born around another star.
Discovered on July 1, 2025, by the ATLAS survey in Chile, 3I/ATLAS is only the third confirmed interstellar interloper, following 1I/ʻOumuamua (2017) and 2I/Borisov (2019). Unlike the rocky ‘Oumuamua, 3I/ATLAS is a hyperactive comet. Recent data from the Atacama Large Millimeter Array revealed that the comet is “bizarrely enriched” with methanol and carbon monoxide concentrations up to four times higher than those typically found in “home-grown” comets from our own Oort Cloud.
Friday’s “closest approach” saw the comet positioned near the bright star Regulus in the constellation Leo. While the object stayed too faint for the naked eye, professional observatories captured high-resolution images showing a “wispy, contorted tail” sculpted by solar winds. What’s really unique is that the comet was also photographed by NASA’s Perseverance rover and the HiRISE camera on the Mars Reconnaissance Orbiter as it whizzed past the Red Planet earlier this fall.
“This is a historic opportunity to observe a true interstellar body up close… It provides an entirely new perspective on the birth and evolution of other solar systems,” a report from NASA’s Center for Near Earth Object Studies stated.
“It seems really chemically implausible that you could go on a path to very high chemical complexity without producing methanol,” NASA astrochemist Martin Cordiner noted, pointing out how the comet’s “alien” chemistry serves as a laboratory for interstellar building blocks of life.
Interstellar comets are essentially “time capsules” from other stellar neighborhoods. Because 3I/ATLAS is currently heating up as it exits the inner solar system, it’s sublimating (turning ice into gas) at a high rate, letting scientists analyze its internal composition through spectroscopy. The comet is racing through space at a staggering 130,000 miles per hour (209,000 kph), the highest velocity ever recorded for a visitor to our system.
Having completed its flyby of Earth, 3I/ATLAS is now headed toward Jupiter, where it’s expected to pass within 33 million miles in March 2026. Astronomers expect to track the object until at least 2028 before it crosses Neptune’s orbit and returns to the void of interstellar space, never to be seen again.
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