It seems like every day there's something new about exoplanets. A new study published in Nature is challenging how scientists think planets form. Turns out, the process might be much faster than previously thought. And there might be far more stars harboring planets than we think, too.It all began with a curious finding: disappearing dust.
A team of astronomers analyzed data from the Infrared Astronomical Satellite (IRAS), which surveyed more than 96 percent of the sky in 1983. They found a cloud of dust circling a young star in the Scorpius-Centaurus stellar nursery. Known as TYC 8241 2652 1, the star was distinctive because of the cloud of dust radiating infrared energy surrounding it; the dust was absorbing energy from the star and radiating it in the infrared range.They looked at the star again in the mid-infrared range in 2008 and 2009 using the Gemini South Observatory in Chile. The 2008 infrared emission pattern was similar to the 1983 measurement, but the 2009 measurement showed that the infrared emission had dropped by nearly two-thirds.NASA’s Wide-field Infrared Survey Explorer (WISE) looked at the same star in 2010 and found that the dust cloud around TYC 8241 2652 1 had almost entirely disappeared. The scientists confirmed their findings with the Japanese AKARI telescope and the European Space Agency’s Photodetector Array Camera and Spectrometer (PACS) at the Herschel Space Observatory. Every measurement said the same thing: the dust was gone.The discovery raised more questions than it answered. Warm dust surrounding a star is thought to be the raw material that makes planets. The most common model has particles accreting to form solid bodies over time, but scientists don’t have a clear understanding of how long the process takes.__“The most commonly accepted time scale for the removal of this much dust is in the hundreds of thousands of years, sometimes millions,” says Inseok Song, an assistant professor of physics and astronomy in the UGA Franklin College of Arts and Sciences. But if the gas disappeared in three years, that's really fast for a new planet to be born. Or, it means planets form a lot faster than we thought.But it could be that the dust was expelled from the star's orbit. If the particles are small enough, somewhere on the order of a hundred times smaller than a grain of sand, the constant stream of photons from the star could push them away from its orbit.Carl Melis, a postdoctoral fellow at UC San Diego likens the discovery to a classic magic trick. “Now you see it, now you don’t,” he says. “Only in this case we’re talking about enough dust to fill an inner solar system, and it really is gone.”Astronomers typically looks to gas clouds to catch planetary formation in action, but if planets form in years instead of hundreds of thousands of years, there may be loads more planets out there that we just can't observe yet. In the search for another habitable world and distant solar systems, it's opening up a world (no pun intended) of possibilities."People often calculate the percentage of stars that have a large amount of dust to get a reasonable estimate of the percentage of stars with planetary systems, but if the dust avalanche model is correct, we cannot do that anymore," says Song. "Many stars without any detectable dust may have mature planetary systems that are simply undetectable."Scientists will need to pursue more research before making a definitive statement about the disappearing gas cloud. Likely they will compare measurements from 1983 with data from modern telescopes to systematically search for other stars that have rapidly depleted — or replenished — their dust clouds. Ultimately, the goal is for a clear picture of how planets are born.
Inseok Song
Advertisement
_Or, it means planets form a _lot_ faster than we thought._
Advertisement