Will we send a spacecraft to intercept 3I/ATLAS?
Scientists first spotted 3I/ATLAS, the 3rd interstellar visitor ever identified in our solar system, in early July 2025. And since then, one question has been asked countless times: will we send out a spacecraft to take a closer look? On August 21, EarthSky’s Will Triggs spoke to University of Edinburgh astronomer Colin Snodgrass to find out the answer. Plus, Colin talked about ESA’s Comet Interceptor, an upcoming spacecraft that will be primed to intercept future interstellar objects. Watch in the player above, or on YouTube.
3I/ATLAS shrinks again
On August 7, 2025, NASA shared a new image of 3I/ATLAS (above) – the world’s 3rd known interstellar object – as well as provided an updated estimate of the size of the object’s nucleus, or core. Shortly after the object was first identified on July 1, 2025, 3I/ATLAS was estimated to have a diameter of about 20 km (12 miles). Then in late July – using data from the new Vera C. Rubin Observatory in Chile – the size estimate dropped to 10 km (6 miles). The latest analysis uses data from the NASA/ESA Hubble Space Telescope. It reduces the estimated diameter of 3I/ATLAS’s nucleus still further, to 5.6 km (3.5 miles).
And, the astronomers using Hubble data said, the object could be even smaller, as small as 320 meters (1,050 feet) across!
Plus, as you can see from the image, 3I/ ATLAS is looking more and more comet-like as it approaches our sun. It’s currently between the orbits of Mars and Jupiter.
The two previous known interstellar objects are 1I/ ‘Oumuamua and 2I/Borisov. ‘Oumuamua’s size is thought to be about 200 meters across at its widest (you’ll recall it has an elongated shape). And Borisov is thought to be less than a kilometer across.
Hellbound and Down 