Hubble's Bizarre X-Shaped Slow-Motion Asteroid Collision

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In January, something mysterious was spotted lurking in the asteroid belt between the orbits of Mars and Jupiter. The eerie comet-like feature — sporting a long tail of dust being swept back by the sun’s radiation pressure — was thought to be a rare asteroid/comet hybrid, but when the Hubble Space Telescope took a closer look, a bizarre shape formed.

An “X” pattern emerged, revealing to astronomers that they were actually looking at the site of a recent (and equally as rare) asteroid-on-asteroid collision a little over 100 million miles from Earth. The pattern was believed to be the debris of the smash expanding into space. However, all’s not what it seems.

BIG PIC: Mystery Comet or Asteroid Collision?

According to Hubble scientists that have been tracking the debris cloud (called P/2010 A2), the asteroid collision didn’t happen recently, it actually happened last year, most likely around February or March 2009.

“We thought this event had just occurred,” said David Jewitt, UCLA astronomer and lead scientist of the Hubble observation, in today’s press release. “We expected the debris field to expand dramatically, like shrapnel flying from a hand grenade.”

This chance observation by ground observatories caused a rush to get Hubble turned around and look at the event. After all, catching a once-in-a-lifetime glimpse of the exploding debris of colliding two space rocks would be over quickly. But in actuality, the debris cloud was expanding much slower than expected.

“We found that the object is expanding very, very slowly and that it started not a week but nearly a year before our January observations,” Jewitt added.

Although asteroid collisions are predicted to occur roughly once a year, spotting the resulting debris cloud requires a lot of luck. These events are crucial to our understanding of how the solar system — and other star systems — evolved, hence the rush to use Hubble to analyze P/2010 A2.

“These observations are important because we need to know where the dust in the solar system comes from, and how much of it comes from colliding asteroids as opposed to ‘outgassing’ comets,” Jewitt continues. “We can also apply this knowledge to the dusty debris disks around other stars, because these are thought to be produced by collisions between unseen bodies in the disks. Knowing how the dust was produced will yield clues about those invisible bodies.”

Hubble kept an eye on P/2010 A2 from January to May 2010, resolving a point-like object approximately 120 meters wide followed by the X-shaped debris field. It is thought the 120-meter-wide object is what remains of the larger asteroid after impact. The smaller asteroid is estimated to have been 3 to 5 meters wide before it was pulverized. The pair were probably traveling at a speed of 11,000 miles per hour, generating an explosion of comparable energy to the detonation of a small nuclear weapon.

The X-shape was most likely caused by the irregular shape of one or both of the asteroids — if they were smooth and spherical, the debris cloud would have been far more symmetrical.

It’s events like these that remind us that we are still in an evolving and dynamic solar system where asteroids are still grinding away, shattering and occasionally generating some powerful fireworks. What’s more, if the collision of P/2010 A2 is typical, perhaps astronomers have more time to look out for the debris clouds of these space rock clashes.

Image credit: NASA, ESA, and D. Jewitt (UCLA)

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