/

Breakup of asteroid witnessed for first time

Sighting boosts theory of how sunlight can spin space rocks until they split

Reuters

Scientists have observed for the first time an asteroid breaking apart, crumbling into at least 10 pieces in a kind of slow-motion celestial train wreck.

The rocky asteroid, named P/2013 R3, was one of the innumerable objects populating the crowded asteroid belt between the orbits of Mars and Jupiter, roughly three times farther away from the sun than Earth.

Asteroids have broken apart many times over the eons, but never before have scientists been able to witness it. The dramatic disintegration was first noticed through telescopes in Arizona and Hawaii, and scientists then got a better look using the orbiting Hubble Space Telescope.

“After looking at the asteroid belt for a couple of hundred years — the first one was discovered in 1801 — to find a new thing like this is really exciting,” said David Jewitt, a University of California, Los Angeles, astronomer who led the research.

The findings were published in Astrophysical Journal Letters.

The asteroid was probably around 600 meters in diameter and no more than about 1 km in diameter before it began to disintegrate, Jewitt said. The breakup unfolded over a period of several months late last year.

The Hubble telescope detected at least 10 fragments, each with cometlike dust tails. The four largest pieces each had a diameter of up to 400 meters.

The scientists do not think the asteroid was destroyed in a collision with another object in part because the way it is breaking apart — the fragments are drifting slowly at around a 1.6 kph — does not suggest a violent impact. In addition, the 10 fragments did not all emerge at one time, as they would in an impact, with their appearance staggered over many months, Jewitt said.

They also think it is unlikely the asteroid fell to pieces due to the pressure of interior ice warming and vaporizing because it simply would be too cold for that to occur.

Instead, they said, the fragmentation was probably the result of the subtle but inexorable effect of sunlight over many, many years causing the asteroid to spin at a slowly increasing rate until it became unstable and ruptured. This phenomenon, known as the YORP effect, has been debated by scientists but never previously reliably observed.

“This is a really bizarre thing to observe. We’ve never seen anything like it before,” said Jessica Agarwal of the Max Planck Institute for Solar System Research in Germany. “The breakup could have many different causes, but the Hubble observations are detailed enough that we can actually pinpoint the process responsible.”

When struck with sunlight, objects radiate heat back into space. This exerts a torque on them, leading to a spin.

“That net force due to sunlight is very, very weak. But on long time scales, it can push asteroids around,” Jewitt said. “So this is probably the way asteroids die in many cases. They spin up and blow themselves apart. And in the process, they make dust and debris that populates the inner solar system.”