NASA Activates Planetary Defense Protocol for Interstellar Comet 3I/Atlas: Scientists Baffled by “Anti-Tail” Phenomenon

Credits: TalesOnTheGo / YouTube

In July 2025, astronomers involved with the ATLAS survey detected an object that immediately countered expectations. Now officially called 3I/Atlas, at 45 km in diameter, it has caused NASA to activate a planetary defense protocol, not due to collision concerns but instead because of the object's anomalous behavior.

Analysis of the spectrum showed large amounts of nickel, with no iron, a chemical fingerprint never seen in any comet in our system. To add even more, its coma is composed of carbon dioxide, water, nitrogen, and carbon monoxide, in ratios that are unlike what we have seen before.However, most concerning was the comet’s “anti-tail,” a stream of particles that points toward the Sun rather than the usual direction, thus, anti-gravity working against the known laws of radiation pressure.

Although 3I/Atlas is approximately 240 million km from Earth, it took on unpredictable accelerations and movements that could not be explained by gravitational models.Harvard astrophysicist Avi Loeb posited that it might be performing an "Oberth maneuver", a propulsion technique characteristic of advanced spacecraft. Most scientists in the field are quick to recoil in rejection, but nevertheless privately confess to a feeling of unknowing, or ‘something about I/Atlas that does not fit.’ For the first time in space science history, NASA states that it is not ruling anything out.

References :

https://www.esa.int/Space_Safety/Planetary_Defence/ESA_tracks_rare_interstellar_comet

https://avi-loeb.medium.com/the-international-asteroid-warning-network-initiated-a-campaign-to-monitor-3i-atlas-d2a698859747