Latest Comet 3I/ATLAS news: One day until the comet is closest to Earth!
Thursday, Dec. 18, 2025: Your daily feed for the holiday flyby of interstellar comet 3I/ATLAS by Earth.
How comet 3I/ATLAS captured our hearts with mystery
We'll admit it: We would love it if the interstellar comet 3I/ATLAS really was an alien spaceship, but at the end of the day, it's still a comet. Yet that does not mean 3I/ATLAS isn't still completely amazing; otherwise, we wouldn't have covered the comet's passage through our solar system as we've done over the last six months.
Why not read up on the four key things that NASA revealed about the comet in a long-awaited briefing following the reopening of the U.S. government in November? At the event, NASA Associate Administrator Amit Kshatriya explained "we very much want to find signs of life in our universe," before re-iterating, "but 3I/ATLAS is a comet".
Full article: 4 key things NASA just revealed about the interstellar comet 3I/ATLAS.
Is comet 3I/ATLAS really a comet?
You've probably heard all the theories: It's really an alien spaceship. It's changed direction. It spat out a tiny spacecraft.
Well, NASA recently made it official: Comet 3I/ATLAS is just what it looks like - a comet from beyond our solar system. In late November, NASA held a televised press conference to put the comet 3I/ATLAS rumours to bed.
"It looks and behaves like a comet, and all evidence points to it being a comet. But this one came from outside the solar system, which makes it fascinating, exciting and scientifically very important," NASA Associate Administrator Amit Kshatriya told reporters during the press briefing.
Here's the full story on NASA's take on comet 3I/ATLAS.
How far is Comet 3I/ATLAS from Earth right now?
As of 12 p.m. ET today (Dec. 17), Comet 3I/ATLAS is about 166.9 million miles (268.6 million kilometers) from the Earth and closing, ahead of its closest approach on Dec. 19.
You can track comet 3I/ATLAS yourself with the help of NASA's Eyes On The Solar System webpage, which has a "Distance Tool" that allows you to calculate the separation between the comet and any other solar system object included in the simulation.
How to watch the comet 3I/ATLAS Earth flyby
The interstellar comet 3I/ATLAS will make its closest pass by Earth on Dec. 19, and you'll be able to watch its approach live online, but you'll need to tune a bit earlier than you'd think.
Astrophysicist Gianluca Masi of the Virtual Telescope Project will host a free livestream of comet 3I/ATLAS on Thursday, Dec. 18, at 11 p.m. EST Dec. 18 (0400 GMT on Dec. 19), weather permitting. You can watch the livestream here on Space.com.
Masi's livestream will run through comet 3I/ATLAS's closest approach at 1 a.m. EST (0600 GMT), but will depend on good weather from his telescope's observing site.
The comet is too faint to be seen with the naked eye and will be challenging even for small backyard telescopes. Under dark skies, observers with a telescope of 8 inches or larger may be able to spot it as a faint, fuzzy patch of light. Read how to watch the comet 3I/ATLAS flyby live online.
Who discovered Comet 3I/ATLAS?
If you've been as captivated as us here at Space.com by comet 3I/ATLAS's trip through the solar system, you might find yourself wondering exactly how it was discovered. So did we, which is why our own Kenna Hughes-Castleberry took it upon herself to find out — and the result was eye-opening!
What seemed like a normal July night ended up making history when astronomer Larry Denneau at the University of Hawaii's Institute for Astronomy discovered a new moving object while scrolling through data from ATLAS — the Asteroid Terrestrial-impact Last Alert System."I was the person reviewing at the time that 3I popped out of the pipeline," Denneau told Space.com "And at the time, it looked like a completely garden variety new Near Earth Object."
Read the full story behind the discovery of comet 3I/ATLAS here.
Comet 3I/ATLAS: An early Christmas gift for scientists
When 3I/ATLAS is closest to Earth on Dec. 19, all the features that we are looking for will be easier to detect with our telescopes and it has scientists as eager as kids on Christmas.
Comet 3I/ATLAS is the third large interstellar visitor (an asteroid or a comet) known to have passed through our solar system from beyond our solar system. By studying it closely, astronomers hope to learn more about other celestial objects through telescope observations.
"It has since been careening through the interstellar medium of the Milky Way galaxy for billions of years," Darryl Z. Seligman, an assistant professor of physics and astronomy at Michigan State University, wrote in an op-ed. "And we get front-row seats to watch as it gets close to our sun, for what is almost surely the first time it has ever gotten close to a star".
Read the full op-ed on the comet's Earth flyby here.
Comet 3I/ATLAS has last hurrah this week
Good morning, Space Fans! As of today, we are T-2 days until the interstellar comet 3I/ATLAS makes its closest approach to Earth and then we'll have to say our goodbyes.
Whether or not you're in Team Comet or Team "Could It Be A Spaceship?" 3I/ATLAS has dominated the comet conversation since its discovery on July 1 by the ATLAS telescope in Chile. On Friday, Dec. 19, 2025, the comet will be at its closest to Earth at a range of roughly 168 million miles (270 million kilometers) before heading out of our solar system for good.
Over the next two days, we'll chronicle comet 3I/ATLAS's Earth flyby, and revisit its passage through our solar system — and its legacy.
Read our full preview of the comet's Earth flyby.
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