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A year ago, on July 1, 2025, astronomers spotted a captivating new object passing through our solar system. Detected by the Asteroid Terrestrial-impact Last Alert System (ATLAS), this object stood out as something extraordinary. Racing past at an unprecedented speed, the comet, known as 3I/ATLAS, is only the third interstellar object ever observed.
Originating from another star, this transient visitor is now heading out of the solar system at over 60 kilometers per second, never to return. The discovery made headlines across the globe, with some sensational claims suggesting it might be an alien spaceship—though that was more speculation than fact, distracting from the true significance of the find.
A recent study published in Nature by a team led by Martin Cordiner from NASA’s Goddard Space Flight Center provides new insights into the comet’s origins. Their findings suggest 3I/ATLAS is a genuine relic from our galaxy, predating our solar system by billions of years.
What Are Interstellar Objects?
Planetary systems are often chaotic. Besides planets, they contain countless smaller remnants—debris leftover from their formation. Much of this debris follows unstable orbits and is periodically expelled into interstellar space due to gravitational interactions with planets. These objects, such as comets and asteroids, then drift through the vastness between stars.
It has long been theorized that if planetary systems are common across the universe, then these systems produce and eventually shed countless rocky and icy bodies. The space between stars should be filled with this debris—ancient and newly formed—much of which never comes close enough to other stars to be observed. However, with advancements in technology, we’ve now identified a handful of such interstellar visitors, including ’Oumuamua, Borisov, and ATLAS.
An Ancient, High-Speed Visitor
Scientists quickly recognized that 3I/ATLAS was hurtling through space at incredible velocity. At its closest approach to the Sun, it was traveling faster than 68 km/s, and even before feeling the Sun’s gravitational influence, it was moving at over 58 km/s. Such speeds hinted that this object was not typical.
By analyzing its orbit within the Milky Way, researchers concluded that 3I/ATLAS is likely much older than our solar system. It probably originated from the galaxy’s “thick disk”—an ancient stellar population that predates the Sun.
Unraveling Its Cosmic Ingredients
To better understand its history, scientists used the James Webb Space Telescope and the Atacama Compact Array to observe 3I/ATLAS in infrared and microwave wavelengths. These observations revealed that the comet’s emitted gases contained significantly less carbon-13, a heavier isotope of carbon, compared to similar objects in our solar system.
This isotope ratio is key because the production of carbon-13 occurs within the interiors of stars over cosmic timescales. Stars more massive than the Sun convert carbon-12 into carbon-13 through a process called “hot bottom burning.” Over billions of years, this increases the proportion of carbon-13 in the galaxy.
The very low levels of carbon-13 in 3I/ATLAS suggest it formed around 12 billion years ago, during the early years of the galaxy, when the abundance of this isotope was still low. This makes it an ancient relic from the galaxy’s infancy.
What’s Next?
The Vera Rubin Observatory, situated atop a mountain in northern Chile, boasts the largest camera ever mounted on a telescope, designed for rapid, wide-angle sky surveys. It is perfectly equipped to spot interstellar objects as they zip through the solar system. Forecasts suggest this observatory could detect dozens more such visitors over the next decade.
Each interstellar object discovered so far has been unique, but with increased detection capabilities, scientists will start to see these objects as part of a larger population. This will enable a deeper understanding of star and planet formation in our galaxy, revealing the history embedded in these cosmic travelers.
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