Anatomy of an Asteroid Breakup


A team of scientists has observed the breakup of an asteroid as it orbits the Sun. In a new study, they reveal what they’ve learned from their ground- and space-based observations of this disintegration.

Hubble R3

These Hubble images show the fragments of R3 in higher resolution over the span of October 2013 to February 2014. [Jewitt et al. 2017]

Observations of Disintegration

Active asteroids are objects that move on asteroid-like orbits while displaying comet-like behavior. The cause of their activity can vary — ranging from outgassing as the asteroid heats up in its solar approach, to expelled debris from a collision, to the entire asteroid flying apart because it’s spinning too fast.

Led by David Jewitt (University of California at Los Angeles), a team of scientists has analyzed observations of the disintegrating asteroid P/2013 R3. The observations span two years and were made by a number of telescopes, including Hubble, Keck (in Hawaii), Magellan (in Chile), and the Very Large Telescope (in Chile).

fragment schematic

A schematic diagram of the different fragments of R3 and how they relate to each other. Black numbers estimate the fragment separation velocities; red numbers estimate the separation date. [Jewitt et al. 2017]

Jewitt and collaborators then used these observations — and a bit of modeling — to understand what asteroid R3 was like originally, what its pieces are doing now, and what caused it to break up.

Cause of the Breakup

The team found that P/2013 R3 broke up into at least 13 pieces, the biggest of which was likely no more than 100-200 meters in size. The original asteroid was probably less than ~400 m in radius.

By measuring the velocities of the fragments in the various observations, Jewitt and collaborators were able to work backward to determine when each piece broke off. They found that the fragmentation process was spread out over the span of roughly 5 months — suggesting that the asteroid’s breakup wasn’t impact-related (otherwise the fragmentation would likely have been all at once rather than gradual).

fragmentation timeline

Timeline of the destruction of R3. Calendar dates are in black, day-of-year dates are in red. The letters below the timeline indicate observations. [Jewitt et al. 2017]

So if it wasn’t an impact, what caused the breakup of R3? Tidal stresses are unlikely; the asteroid wasn’t close enough to the Sun or a planet to experience strong pulls. Gas pressure from sublimating ice also falls short of being strong enough to have caused the disruption, according to the authors’ calculations.

The authors conclude that the most plausible cause of R3’s breakup was rotational instability. If an asteroid is made up of a collection of rocky material loosely gravitationally bound in what’s known as a “rubble-pile” composition, then it tends to fly apart if the asteroid spins faster than once every ~2.2 hours. The authors show that torques from radiation or anisotropic sublimation could have driven R3 to spin this quickly on a relatively short timescale.

A Dusty End

zodiacal light

Zodiacal light, caused by scattering by dust in the Zodiacal Cloud. [ESO]

Lastly, Jewitt and collaborators examine the debris cloud released by the breakup of R3. They use these observations to estimate how much debris disrupted asteroids likely contribute to the Zodiacal Cloud, the cloud of dust found in our solar system, primarily between the Sun and Jupiter.

The authors estimate that the fractional contribution by asteroids like R3 is roughly 4% — consistent with models that suggest that asteroid dust is a measurable, but not dominant, contributor to the Zodiacal Cloud. Future sky surveys will allow us to better examine this contribution.


David Jewitt et al 2017 AJ 153 223. doi:10.3847/1538-3881/aa6a57

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