March 9, 2014
Hubble Space Telescope observed P/2013 R3 asteroid as it was falling apart all by itself. The first ever observed asteroid that disintegrated without an impact involved is probably caused by the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect.
Asteroid P/2013 R3 pictured falling apart due to the YORP effect. Credit: NASA, ESA, D. JEWITT (UCLA)
Seeing a comet fall apart is normal – it is made of ice and when it gets too close to the Sun, ice rapidly sublimates to vapor and the comet loses its structure and breaks apart. Asteroids are made of rocks, so seeing an asteroid fall apart without an impact is a sensation. The latter is exactly what Hubble Space Telescope observed in the asteroid belt between orbits of Mars and Jupiter and it marks the first time we have observed such a phenomenon.
What looked like three objects surrounded by Earth-sized dusty envelope to Keck Telescope, are actually ten pieces of a single asteroid P/2013 R3, all of them with comet-like tails made of dust. Four largest pieces are about 400 meters across and they are all moving at 1.5 kilometers per hour.
"This is a really bizarre thing to observe — we've never seen anything like it before," says Jessica Agarwal, the Max Planck Institute for Solar System Research, Katlenburg, Germany. "The break-up could have many different causes, but the Hubble observations are detailed enough that we can actually pinpoint the process responsible."
The speed and direction of moving pieces rules out collision with another asteroid. The process that causes comets to break apart is also not likely, keeping in mind that the distance of the asteroid to the Sun is too great for ice in rocks to melt rapidly.
The most likely cause is the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect. The YORP effect is a phenomenon where an asteroid begins to spin because it emits infrared radiation only from one side. The process goes something like this:
First, the Sun's radiation heats up only one side of an asteroid. Then, as the asteroid naturally rotates, this warmer side is now in the shadow and it begins to emit infrared radiation as it cools down. By emitting radiation, it starts to spin slightly faster. Similar thing, but on a larger scale, can be noticed in neutron stars that spin by giving away energy via magnetic field. Finally, over millions of years, it reaches spinning speeds where centrifugal force is so great, the asteroid breaks apart.
For the YORP effect to work, it is believed an asteroid has to have weak internal structure. It is likely that P/2013 R3 was more of a "rubble pile" caused by previous, non-destructive collisions, and not a single, homogeneous rock to begin with.
"This is the latest in a line of weird asteroid discoveries, including the active asteroid P/2013 P5, which we found to be spouting six tails," says Agarwal. "This indicates that the Sun may play a large role in disintegrating these small Solar System bodies, by putting pressure on them via sunlight."