The Hubble Space Telescope has photographed a never-seen-before breakup of an asteroid. Named P/2013 R3 (Catalina-PanSTARRS), it was discovered last September 15 by the Catalina and Pan-STARRS sky surveys as a faint, slightly fuzzy object. Two weeks later, the giant Keck Telescope in Hawaii took a closer look and saw not one but three separate pieces cruising along convoy-style in a dust cloud of their own making.
Animation showing the break up of P/2013 R3
By December it had crumbled into ten pieces, the four largest of which measure about 650 feet (200 meters) across or nearly two football fields apiece. The Hubble data show the fragments are drifting apart at the leisurely rate of just under 1 mile per hour (1.5 km/hr) or about the speed of someone walking while texting.
“This is a really bizarre thing to observe — we’ve never seen anything like it before,” says co-author Jessica Agarwal of the Max Planck Institute for Solar System Research, Germany. “The break-up could have many different causes, but the Hubble observations are detailed enough that we can actually pinpoint the process responsible.”
Astronomers have ruled out a collision, which would have happened suddenly and sent pieces flying apart at much great speeds. Shattering from the pressure of vaporizing ices in its interior also seems unlikely given the asteroid’s distance of 298 million miles (480 million km) from the sun – believed too cold for any ice it might possess to suddenly turn to vapor and pry the body apart. Besides, if it did contain ice, P/2013 R3 wouldn’t be considered an asteroid anymore but a main belt comet, an asteroid-like object between Mars and Jupiter that occasionally flares up as a comet.
So what could be responsible for perpetrating killing off an asteroid? Scientists suspect it was YORP up to his old tricks. YORP or the Yarkovsky-O‘Keefe-Radzievskii-Paddack effect requires only the light touch of sunshine to get rolling.
Sunlight absorbed by P/2013 R3 is re-emitted as heat. Assuming the asteroid is irregular in shape – and most are because they’re so small – some areas get hotter and give off more heat than others. The imbalance causes a torque on the asteroid, increasing its spin rate.
Many asteroids are “rubble piles” of individual objects held together by gravity rather than solid rocks. Collisions with other asteroids over the 4.5 billion year lifetime of the solar system have shattered and pulverized their interiors. Primed to fall apart, the spin-up from YORP causes the asteroid to come apart at the seams. Pieces that were loosely-bound can drift away due to centrifugal forces; fresh dust exposed creates an enveloping comet-like cloud of debris. Pretty darn cool.
We’ve seen one other instance of an asteroid breaking to pieces when Hubble photographed the aftermath of a head-on collision between the peculiar comet-like asteroid P/2010 A2 and a smaller asteroid in January 2010. But this is the first time ever we’ve watched an asteroid fall apart of its own accord.
“This indicates that the Sun may play a large role in disintegrating these small Solar System bodies, by putting pressure on them via sunlight,” said Agarwal.
Much of P/2013’s debris, weighing in at around 200,000 tons, will spiral its way into into the sun, but a portion could one day light up Earth’s skies as a lovely meteor shower. Amazing isn’t it how nature shares its incredible stories when we pay attention.