Why did all the planet-forming dust around this star disappear in only three years?

Illustration for article titled Why did all the planet-forming dust around this star disappear in only three years?

Back in 1983, astronomers discovered a star 450 light-years away that was surrounded by a cloud of dust — a textbook example of a solar system in the making. Now, nearly thirty years later, the cloud has suddenly and mysteriously disappeared.

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This discovery could mean that everything we thought we knew about the birth of planets is wrong.

This is one of those observations that, on the face of it, doesn't make a lot of sense. Astronomers have always believed that it takes hundreds of thousands of years — if not millions — for the dust orbiting a young star to congeal and form planets. This recent observation, however, indicates that planets may form significantly faster than we thought. Or alternatively, that these dust clouds behave in ways unknown to us.

Making sure the data is correct

To confirm and cross-reference this strange discovery, researchers were pooled from a number of institutions, including universities from Georgia, San Diego, Los Angeles, California-Polytechnic, and Australia. This was a team effort.

Illustration for article titled Why did all the planet-forming dust around this star disappear in only three years?

What troubled these scientists was that the cloud of dust circling a star in the Scorpius-Centaurus stellar nursery simply disappeared within the span of three years.

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The researchers used data from a wide array of sources, including a mid-infrared imager at the Gemini South Observatory in Chile, NASA's Wide-field Infrared Survey Explorer, the Japanese AKARI telescope, and the European Space Agency's Photodetector Array Camera and Spectrometer. Looking at all the data provided by these instruments, the scientists could not help but conclude that, from the period 2008 to 2009 the infrared emissions dropped by nearly two-thirds (indicating a dramatic decrease in dust), and that by 2010 the dust cloud had all but vanished.

Okay, so what happened to all the dust?

With the data largely confirmed, the scientists were forced to come up with theories explaining the anomaly.

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One suggestion, as absurd as it sounds, is that it doesn't take long for planets to form given certain conditions — what is dubbed "runaway accretion." In such a scenario, the growth of dust and rocks snowballs quickly, leading to the rapid, nearly instantaneous formation of planets. If true, this would completely reset our notions of just how quick and easy it is for planets to form around a star.

But three years? Really? It would be nice to see computer models prove this idea. Moreover, if this theory is true, a new planet should be orbiting this star. Hopefully, using more advanced telescopes than we have now, we might someday be able to find it.

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Another possibility is what the scientists call "collisional avalanche." This theory suggests that the dust was expelled from the sun's orbit. Because these dust particles are so small — smaller than a grain of sand — the constant stream of photons emanating from the sun could push them away and into each other until they leave the sun's orbit. The problem with this theory, however, is that it makes planetary formation sound rare and difficult, which we know it certainly is not.

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And yet another theory suggests that the sun swallowed all the dust in one gigantic gulp. Again, another unsatisfying answer. As Nola Taylor-Redd noted in a recent Space.com article, "[This] theory, known as the collisional cascade model, would likely require time scales longer than two years to clear the dust from the system."

Clearly more work needs to be done, and the researchers are planning their next move. Specifically, they want to analyze old observations like the one made in 1983 and compare them to new data pulled from modern telescopic techniques, to make a systematic search for other stars that may have recently gone through a similar phase.

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These results were published today (July 5) in the journal Nature.

Sources: Daily Mail, Space.com.

Images via Space.com.

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DISCUSSION

If giants are common in inner solar systems (they seem to be), then its possible a gas giant or even a system of gas giants collected the material... Its also possible that there's an eccentrically orbiting giant that wildly varies its distance from the parent star, which would allow it to sweep up large amounts of material on the inbound/outbound trajectories without creating too much wobble that we'd notice with limited observations.

Of course, something else could have collected the dust and material. We could have just seen the "billion-billion to one" shot of watching an advanced interstellar species mine a lifeless system for material. Or if it turns out that the system has rocky inner planets, we may have just seen a species prep a star system for eventual terraforming and colonization.

If you're a really advanced species, and you want the perfect place to expand and your technology is sufficiently advanced, you choose a very young star with the qualities you would like for your species. No fuss, no muss. No life has formed there yet, nothing to interfere with your plans, no pesky intergalactic Greenpeace telling you "better not touch the morklings in the oceans..." The world would preferably be one with bucketloads of material to harvest - then you just wait for the star to settle down a bit, watch to make sure you're not going to end up with gas giants in the inner system, then collect the unused material as resources when rocky worlds of a sufficient size have formed. A little terraforming, perhaps a bit of solar-forming and voila - instant colony for you and your billion fellows - a nice cottage world to get away from the rough and tumble drudgery of intergalactic city life. Easy resources near by too, because its not to far away from a stellar nursery.