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.

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.

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.

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.

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.

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.

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.

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

Sources: Daily Mail, Space.com.

Images via Space.com.