Scientists Can’t Explain Why Some Asteroids Suddenly Change Direction — Cosmic Mysteries Deepen

 

In a stunning series of observations spanning the past year, astronomers have documented celestial objects — including asteroids and interstellar visitors — that shift their paths in ways not predicted by gravitational models alone. These unexpected changes are forcing researchers to rethink how tiny forces and unseen processes can alter the motion of rocky bodies across the solar system.

 

Recent attention has focused on the interstellar comet 3I/ATLAS, first detected on July 1, 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Chile. This object is only the third confirmed interstellar visitor ever seen, meaning it comes from outside our solar system and follows a hyperbolic trajectory that takes it through and beyond the Sun’s influence. Wikipedia

What has startled many researchers is that the motion of 3I/ATLAS appears to deviate from what gravity alone should produce. Recent analyses suggest a measurable non-gravitational acceleration, meaning the object’s speed and direction aren’t explained solely by the Sun’s gravitational pull. Medium+1

This kind of behaviour was first identified — in even stranger fashion — in the interstellar object ‘Oumuamua in 2017. That object displayed a tiny but persistent extra push that could not be fully explained by simple models of how comets and asteroids behave.

 

What “Non-Gravitational Acceleration” Means in Space

Non-gravitational acceleration usually refers to motion caused by forces other than gravity. For many comets, this can be explained by outgassing, where heat from the Sun causes ice in a comet to vaporize, producing a tiny jet-like reaction that can nudge the body’s trajectory. It’s the same principle that powers a rocket — but on a much, much smaller scale.

However, even after accounting for the expected outgassing from 3I/ATLAS and similar bodies, some of the observed trajectory tweaks still don’t add up. This has led scientists to explore additional mechanisms that could subtly alter motion. Medium

 

The Yarkovsky and YORP Effects — Radiation Can Nudge an Asteroid

One widely accepted explanation for unexpected asteroid motion over long timescales is the Yarkovsky effect — a process where sunlight heats an asteroid’s surface, and the re-radiated heat produces a tiny thrust. Although extremely subtle, this force can slowly change an asteroid’s orbit over years or decades. Wikipedia

A related process, the YORP effect (named after scientists Yarkovsky, O’Keefe, Radzievskii, and Paddack), can alter not just orbital motion but rotation rates due to uneven heating and reflection around the object’s surface. Wikipedia

Both effects are widely accepted in astrophysics and help explain long-term changes in small body motion that ca