The UN's International Asteroid Warning Network is closely watching comet 3I/ATLAS. Here's why.

As the interstellar comet 3I/ATLAS prepares for its closest approach to Earth on Dec. 19, it's being monitored not just by space agencies but also the United Nations.

The comet, which will come within roughly 167 million miles (270 million kilometers) of our planet, will be tracked by telescopes around the world so astronomers can pinpoint its location and make predictions about future objects like it.

The U.N.'s International Asteroid Warning Network (IAWN) is about halfway through its 3I/ATLAS observing campaign and expects to publish its findings in a peer-reviewed journal next year, James Bauer, a small-bodies node principal investigator at IAWN and a research professor in the University of Maryland's astronomy department, told Live Science. The network consists of more than 80 observatories and citizen scientists around the world doing active research on near-Earth objects, such as comets and asteroids.

NASA coordinates the IAWN and the network's observing campaigns, Bauer said, and 3I/ATLAS is the first interstellar object to be tracked since the campaigns began in 2017. (Notably, the potentially hazardous near-Earth asteroid Apophis was observed by IAWN in 2020 and 2021, and a new campaign is expected between 2027 and 2029 as the asteroid makes a safe-but-close approach to Earth.)

"The idea behind these campaigns is really to strengthen the technical capabilities for measuring sky positions, which we call astrometry, for asteroids and comets," Bauer said of IAWN's work. The investigators will be testing a new astrometry technique to track the pathway for 3I/ATLAS, which can be helpful for determining how to send a spacecraft to a similar comet in the future.

"We want the community to use the latest and greatest techniques," Bauer said. (Bauer also serves as principal investigator for the NASA Planetary Data System's small bodies node, which archives, catalogs and distributes scientific data related to comets, asteroids and interplanetary dust.)

Tracking 'a comet's comet'

IAWN had been planning an observing campaign like this since October 2024, so 3I/ATLAS was a late-but-fortuitous arrival when it was first spotted in late June. The interstellar comet's upcoming close approach coincides well with the team's planned observing schedule, and because 3I/ATLAS was visible in the network's observatories and of high interest, it seemed like a great fit, Bauer said.

There are challenges in accurately measuring a comet's position, he noted, such as the changing brightness and the variability in its coma, the cloud of gas and dust that extends around the comet’s nucleus and tail as it draws closer to the sun and heats up. These features can inflate the comet’s apparent size and make its location harder to pinpoint.

Luckily, although 3I/ATLAS originated outside the solar system, it's showing such classic comet behavior that it is almost a "comet's comet," Bauer said. For example, it includes components like water and carbon dioxide that are behaving similarly to normal solar system comets.

Community interest has been high. Citizen scientists, observatories large and small, and scientific organizations formed a record 171 campaign participants at the kickoff of IAWN's 3I/ATLAS campaign meeting in October. The mid-campaign teleconference, held Dec. 9 and days before Bauer's interview with Live Science, had 100 campaign participants.

"We've been answering questions from the community — for example, 'How to use the tool? What is the proper format for observing, or for reporting the observations?'" Bauer said.

He said he's grateful for the community's time and interest, as it is helping astronomers refine their ability to report the positions of objects in the sky — including "vigilance" for other near-Earth asteroids and objects that come much closer to our planet.