spaceSpace and Physics

Asteroid Seen Spinning Itself Into Pieces


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer


This is the first time we have witnessed the break-up of an asteroid like this (the images are flipped in Hubble's mirror so that east is to the left). Jewitt et al/The Astrophysical Journal

If, as a kid, you spun yourself around so many times you became dizzy enough to lose your lunch, you might know how the asteroid P/2013 R3 felt (if asteroids were sentient beings). P/2013 R3, R3 for short, is the first main belt asteroid to have been observed disintegrating, and new research attributes the process to excessive spin.

Between August 2013 and February 2014, R3 went from one object to at least 13. Having only been discovered in September 2013, we got to see much of this process. Unsurprisingly, dust was released in the process, enveloping the fragments and making it difficult to see what was happening. However, Professor David Jewitt of the University of California, Los Angeles has offered an explanation of the process.


Although it orbits within the main asteroid belt, risking collisions, Jewitt proposes R3 was not destroyed by an impact. Instead, he thinks it was spinning too rapidly to hold itself together, and centrifugal forces pulled the unfortunate asteroid apart.

We don't know much about R3 prior to the break-up, but the components, with radii of a maximum of 100-200 meters (330-660 feet) would have formed a sphere with a radius up to 400 meters (1300 feet).

Jewitt tentatively proposed this theory for R3's break-up three years ago. Drawing on observations of the fragments and dust from the Hubble Space Telescopes and some of the largest telescopes on Earth, he thinks the evidence is now much stronger.

Such a break-up requires rapid spin, with a period probably less than 2.2 hours. However, if R3 had been spinning like this since its formation it would have broken up long ago. So what gave it the extra spin?


Although classified as an “active asteroid”, rather than a comet, R3 may well have contained some frozen water, and when exposed to sunlight this would have turned to gas, providing torque as it escaped the asteroid's surface. Just 1 gram (0.03 ounces) per second of released water would have been sufficient to induce sufficient spin over a period of less than a million years.

An alternative explanation lies in the YORP effect, where the minuscule energy imparted by photons of sunlight bouncing off an asteroid's angled surfaces produces torque, which generates spin. Unlike a collision, spin induced by either escaping water or the YORP effect can explain why some of R3's fragments broke up themselves so quickly after the initial separation.

In a paper accepted for the Astronomical Journal,and available on, Jewitt calculates that events such as these make a “measurable but probably not dominant” contribution to the Zodiacal Dust Cloud, which orbits the Sun in the same plane as the planets and produces the Zodiacal lights that under ideal conditions can sometimes be seen at dusk.



[H/T: Bad Astronomy]


spaceSpace and Physics
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  • asteroid,

  • break up,

  • angular momentum,

  • YORP effect,

  • Zodiacal dust