Image Credit: NASA/JPL/Cal-tech (Source)

This week, we've had several neat asteroid-centered stories First, an Apollo-class asteroid made an appearance as it passed between Earth and the Moon. Then, yesterday, we finally saw sequential pictures of the never-before-seen demolition of an asteroid.

The asteroid in question, dubbed asteroid P/2013 R3, was first observed on September 15, 2013. When it was originally observed by the Catalina and Pan-STARRS sky-survey telescopes, it merely appeared to be some weird, fuzzy-looking, irregularly shaped object. Then, on October 1st, follow up observations taken on with the W. M. Keck Telescope showed that the little-asteroid-that-couldn't had broken up into three smaller pieces; each piece was encased in a dusty envelope, which, all together, had a diameter that was very similar to that of Earth. After seeing this spectacle, David Jewitt (the leader of the astronomical investigation team that probed into what happened to this asteroid) had this to say: "The Keck telescope showed us that this asteroid was worth looking at with Hubble."


By January of this year, Hubble revealed that the three pieces had become ten: each having a comet-like dust tail. The four largest of which, were about 400 yards (365.76 meters) in diameter (or about the length of four football fields). Now, events like this aren't that unusual. Throughout the last twenty years or so, with the technological progression of sophisticated telescopes, we've seen several near-Earth objects break apart as they approached the Sun, like Comet ISON in the final months of 2013. Such events were typically observed with comets. They are much more fragile and fleeting, mostly because they are largely made up of light components, such as water-ice and bits of other volatiles. Whereas, asteroids are made up of heavier, more sturdy components: like rock and/or metal.  Thus, witnessing something like this is a rare pleasure.

Image Credit: NASA, ESA, D. Jewitt (UCLA)

According to data from the Hubble Space Telescope, the broken pieces of the asteroid are sloooooowly drifting apart at the very lazy speed of 1 mph (1.6 km/h).  The parts have been drifting since the asteroid first began breaking apart last year, and in the most recent pictures we have, new rocky fragments are being observed all the time.  All of this is very interesting, but what is even MORE intriguing is the reason WHY the asteroid is falling to pieces.

Based on the data collected thus far, scientists cannot say definitively if the disintegration is the result of a collision between the asteroid and another object, but they suspect that this scenario is incorrect, as there was no instantaneous or violent impact observed. Plus, if that were the source of the problem, the debris from the huge collision would be expected to travel much faster than snails trudging through mud. Thus, a more sound explanation is required.


One such hypothesis posits that the asteroid exploded because of inner pressure. Said pressure would be an artifact of interior ices warming up and vaporizing. Only, like the above scenario, this one appears to lack observational evidence. Furthermore, this asteroid is far too cold for ices to significantly sublimate. In addition, the asteroid has (presumably) maintained a distance of almost 300 million miles (482.8 million kilometers) from the Sun at any given time in the solar system's history.

With these two hypotheses ruled out, we have pretty much only one left: the asteroid might be disintegrating because of sunlight. Yes, I know this sounds very strange, but specifically, continuous exposure to sunlight might have actively degraded the rotation rate of the asteroid over time, causing it to gradually increase. After a while, this would result in centrifugal force tearing the asteroid apart from the inside out. The disruption of a celestial object, according to the tenets of this phenomenon, called the YORP effect, require another variable, we would need to factor in how minor collisions may have helped contribute to the asteroid's current condition. Perhaps these bumps and bruises made it more susceptible to the consequences of the YORP effect?


A rendering of the YORP effect (Credit: NASA, ESA, D. Jewitt (UCLA), and A. Feild (STScI)

Furthermore, scientists now believe that most small, irregularly-shaped asteroids are damaged this way, making their interiors extremely weak and very chaotic. This was given further credence by Hubble's recent discovery of an asteroid showing off SIX tails (P/2013 P5). Following the detection of this baffling object, astronomers had to reconsider the role sunlight might play in changing the internal pressures of small, rocky bodies, thinking now that this mechanism might be the motivating factor behind the deaths of most small asteroids (less than 1 mile/1.6 km across) in our solar system.

Regardless of how the asteroid died, the 200,000 tons of debris left behind will reappear elsewhere in our solar system, Jewitt says. Most of the debris will, of course, end up eaten by our Sun, but some might enter our atmosphere instead, creating a real-life celestial firework scene, as they fall through our atmosphere and disintegrate.

The full study was published March 6th in "Astrophysical Journal Letters." Additional information can be found here.

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