How Sunlight Spins Space Rocks: New Insights into the YORP Effect

For decades, astronomers believed that the spins of asteroids were shaped almost entirely by violent collisions and gravitational encounters. That story is now changing. As telescopes grow sharper and space missions more precise, scientists are uncovering the surprising truth: sunlight itself can gradually twist, tilt, and even tear apart asteroids. This subtle, long-term influence is known as the YORP effect, and it is rapidly becoming one of the most intriguing topics in planetary science.

What Exactly Is the YORP Effect?

The oddly named YORP effect is an acronym honoring four researchers—Yarkovsky, O’Keefe, Radzievskii, and Paddack—whose work helped reveal how sunlight can alter the behavior of small celestial bodies. In simple terms, YORP describes changes in an asteroid’s rotation caused by sunlight heating and re-radiating from its surface.

Here’s how it works:

• The Sun’s rays strike the asteroid.
• The asteroid absorbs that energy, heats up, and later emits it as thermal radiation.
• Because the surface is rarely uniform—covered in boulders, pits, and odd angles—this re-radiation is uneven.
• The uneven emission produces tiny but constant pushes, effectively acting like miniature thrusters.

Over thousands or millions of years, these tiny pushes add up, accelerating or slowing the asteroid’s spin. In some cases, YORP can even tilt its rotational axis, transforming its future trajectory in subtle but measurable ways.

Real-World Evidence: From Theory to Observation

For a long time, the YORP effect lived mostly in equations and computer models. That changed in the 21st century.

One of the clearest examples is asteroid (54509) YORP, named after the effect itself. Astronomers have measured its rotation speeding up a little more each year. The change is tiny—the asteroid’s day shortens by only a few ten-thousandths of a second annually—but the confirmation was groundbreaking. It showed that sunlight alone can noticeably change the motion of a space rock.

Other observations soon followed:

• Radar data from the Arecibo Observatory and images from the Very Large Telescope revealed unexpected rotational changes in multiple near-Earth asteroids.
• NASA’s OSIRIS-REx mission to Bennu and JAXA’s Hayabusa2 mission to Ryugu demonstrated that so-called “rubble-pile asteroids” are especially vulnerable to YORP. These objects are not solid boulders, but loose clusters of gravel, dust, and rock fragments barely held together by gravity. If their spin speeds up, they can literally reshape themselves—sometimes in real time.

This leads to a fascinating feedback loop:

shape affects YORP, and YORP affects shape. As the asteroid changes form, the thermal thrust changes too, which can redirect its evolution unpredictably.

Cosmic Consequences: YORP’s Long — Term Impact

The YORP effect is not just a scientific curiosity — it can completely alter the destiny of an asteroid.

YORP Consequence Result

• Spin-up to break-up Asteroid sheds material or splits apart
• Formation of binary systems Debris can form a small moon
• Changes in obliquity (tilt) Chaotic, tumbling rotations
• Migration through the

Solar System (with the

Yarkovsky effect) Asteroids can drift into Earth-

crossing orbits

Some astronomers now believe that YORP-driven spin changes are one of the primary reasons so many small asteroids become double systems. When they spin too fast, chunks fly off—sometimes becoming satellites.

Why the YORP Effect Matters to Us

This seemingly gentle force has major implications for humanity:

• Planetary defense: Predicting an asteroid’s future orbit is harder than once believed. Gravity isn’t the only factor anymore—sunlight must be in the equations.
• Space missions: Craft approaching small bodies must account for shifting spin rates.
• Asteroid mining (future prospects): A fast-spinning rubble pile is a terrible mining platform—and YORP might make it spin even faster over time.

In other words, if we want to explore, exploit, or protect Earth from asteroids, we must understand what sunlight is doing to them.

A Subtle Force with a Big Role

The YORP effect is a powerful reminder that the Solar System is not static. Even gentle sunlight—massless, silent, and constant—can sculpt worlds over time. The more we study asteroids, the clearer it becomes that they are dynamic, evolving objects influenced by forces both violent and delicate.

In the end, YORP teaches us something profound: in space, even the smallest nudge, repeated long enough, can change everything.