Astronomers discover rare, self-destructing asteroid

Chuck Bednar for – @BednarChuck

A rare class of so-called “active asteroids” that appear to leave behind a tail of dust and debris similar to that of a comet are travelling so fast that they are essentially making themselves blow up, according to research published Friday in Astrophysical Journal Letters.

For many years, people assumed that asteroids were nothing more than lifeless rocks floating throughout space, but in recent years, experts began discovering signs of activity in these objects, according to CNET. In fact, in 2010, a new sub-type of active asteroid with comet-like tails was discovered, and scientists were at a loss as to why the object was ejecting dust.

Hypervelocity collisions versus rotational disruption

Scientists came up with two predominant possible hypotheses to explain these asteroids. One was that the explosion was the result of a hypervelocity collision with another minor object. The other was that it was launching dust and fragments as a consequence of a phenomenon known as “rotational disruption,” in which the asteroid was spinning so quickly that the large centrifugal forces produced exceed its own gravity and cause it to begin breaking apart.

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In their new paper, a team led by astronomers at the Jagiellonian University in Poland explained that they used the Keck Observatory in Hawaii to observe and measure an active asteroid which was believed to be experiencing rotational disruption. They calculated the rotational speed of the object and found that it was spinning so fast that it was essentially self-destructing.

“When we pointed Keck II at P/2012 F5 last August, we hoped to measure how fast it rotated and check whether it had sizable fragments. And the data showed us all that,” lead investigator Michal Drahus of the Jagiellonian University explained last week in a statement.

He and his colleagues discovered at least four individual fragments of the object, which was established to have impulsively ejected dust in mid-2011, and an extremely short rotation period (3.24 hours) that was fast enough to cause the object to impulsively explode. Essentially, it was spinning so fast that it burst, leaving behind a comet-like trail of dust and fragments.

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“This is really cool because fast rotation has been suspected of catapulting dust and triggering fragmentation of some active asteroids and comets. But up until now we couldn’t fully test this hypothesis as we didn’t know how fast fragmented objects rotate,” explained Drahus.

Measuring periodic fluctuations in brightness

He and his colleagues calculated the rotation period of the target object, P/2012 F5, through measurements of slight periodic fluctuations in brightness. These oscillations occur naturally as the irregular nucleus rotates about its spin axis, they explained, and reflect different amounts of sunlight during a different points in a rotation cycle.

“This is a well-established technique but its application on faint targets is challenging,” said Waclaw Waniak, a researcher at the Jagiellonian University who processed the Keck Observatory data. “The main difficulty is the brightness must to be probed every few minutes so we don’t have time for long exposures. We needed the huge collecting area of Keck II, which captures a plentiful amount of photons in a very short time.”

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While the data collected by Drahus and his colleagues is consistent with the rotational disruption scenario, he noted that possible alternative explanations for the asteroid’s breakup, such as a high speed collision with a smaller object, cannot be completely eliminated at this time.


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