Carl Melis from the University of California San Diego and a team of fellow astronomers have been observing a young sun-like star located about 456 light years away. In observations made before 2009, researchers noted a dense disk made of dust surrounding the distant sun.
According to recent observations by ground telescopes and satellites, this dust cloud has dissipated substantially in only two years’ time. The study, presented in the journal Nature, reports that “The star seems to have gone from hosting substantial quantities of dusty ejecta, in a region analogous to where the rocky planets orbit in the Solar System, to retaining at most a meagre amount of cooler dust.”
The study is based on observed levels of infrared radiation from the distant sun. Over the course of only two years, the infrared heat signature dropped by a factor of 30, suggesting a dramatic change in the dust surrounding the sun.
Other studies have suggested that it is common for young suns to possess such dust disks. Scientists believe that planets form from these disks. Planet formation has never been directly observed, and most scientists believe that the process takes thousands if not millions of years. But the apparent disappearance of the dust surrounding this young star suggests that planet formation—or at least one stage in the planet formation process—may occur much more quickly.
Margaret Moerchen, a researcher at the Leiden Observatory, says: “perhaps the most exciting possibility is that the brightness drop represents a stage of terrestrial-planet formation that occurs so quickly that we have not been lucky enough to glimpse it until now.”
She continues goes on to explain the collisional cascade model: ”gravitationally bound dust grains experience successive cratering or wholly destructive collisions that eventually yield grains small enough to be blown out of the system.” So the rapid drop may actually be explainable by collisions between young planets that result in dust fine enough to be blown from the system, thus explaining the rapid drop in infrared heat signatures. This may, then, be a phase of early planet formation that has not previously been observed.
Fortuitously for astronomers, this model predicts cyclical behavior. Within the next couple of decades, if this model is correct, a new disk of dust should form around the distant sun. This would lend a great deal of credibility to the model. Either way, the study concludes, “this system has clearly undergone a drastic event that promises to provide unique insight into the process by which rocky planets form.”