The interstellar comet 3I/ATLAS, which swept through the inner solar system in late 2025, originated in a primordial planetary system roughly 12 billion years ago, according to an isotopic study published in Nature. That places its formation less than two billion years after the Big Bang, making the object older than the Sun and Earth by a factor of three. The finding, led by researchers at NASA’s Goddard Space Flight Center, marks the first time astronomers have dated an interstellar visitor to the galaxy’s early epoch using direct chemical evidence.

Spectroscopic observations from the James Webb Space Telescope and the ALMA array in Chile captured the comet’s gaseous coma as it receded from perihelion in December 2025. The water ice in 3I/ATLAS contains deuterium at a concentration of 0.98 percent—more than ten times the level seen in solar-system comets and above values measured in local stellar nurseries. Physico-chemical models indicate such enrichment requires water to form on dust grains at temperatures of 30 Kelvin (–243 °C) or lower, conditions typical of a dense, frigid molecular cloud in the early Milky Way. Simultaneously, the ratio of carbon-12 to carbon-13 far exceeds the homogeneous signature found across the solar system, consistent with an origin before later generations of stars had injected heavier carbon isotopes into the interstellar medium.

While the comet’s chemistry opens a window into galactic archaeology, a separate milestone underscores the reach of human-engineered probes. Voyager 1, launched in 1977, will this November cross the distance of one light-day from Earth—nearly 26 billion kilometres. The twin Voyager spacecraft, designed for a five-year mission to Jupiter and Saturn, still return data after almost half a century, using computers with less memory than a modern car key fob. Their longevity, sustained by a rare planetary alignment that enabled the “Grand Tour” of the outer planets, has transformed the outer solar system from points of light into mapped worlds.

Viewed from research centres in the United States and Russia, the two developments illustrate complementary extremes: one object carries a chemical fingerprint from the galaxy’s infancy, the other is a testament to sustained engineering in the present. The next observational milestone for interstellar objects will be the capacity to resolve their composition earlier in their inbound journey, while Voyager’s slowly declining power supply means mission controllers will continue shutting down instruments one by one to stretch operations into the 2030s.