News in Science

Mystery of the missing stellar dust

Dust buster Astronomers are baffled by the sudden disappearance of a planet-forming disc around a distant star.

Scientists say the system has undergone some sort of dramatic event, and solving the mystery may provide a new insight into the birth of our own planet 4.56 billion years ago.

Astronomers including Dr Carl Melis from the University of California, San Diego were studying a thick disc of swirling dust orbiting a star 460 light years away in the constellation Centaurus.

"The star named TYC-8241-2652-1 is similar to the Sun, but a lot younger, about 10 million years old," says Melis.

These planetary dircumstellar discs are where new planets are born, and the disc that disappeared was about the same distance from its host star as Mercury is from the Sun.

Planetary birth

The disc was made up of the collision of rocky boulder-sized objects, asteroids and bigger forming planets.

"This is similar to what was happening in our solar system when the Sun was between 10 million and 100 million years old," says Melis.

Melis and colleagues find these dust discs by looking for the infrared radiation they emit.

"We spot these discs and tag them for follow up," says Melis.

"We don't usually expect something to happen so we take our time. But when we checked back about half a year later we found over half the infrared light being emitted from the disc had suddenly gone.

"We thought something must have gone wrong with our instruments so we waited for fresh data from NASA's Wide-field Infrared Survey Explorer (WISE) space telescope.

"But when the WISE data came in, it showed that the disc was now completely gone," says Melis.

Mystery deepens

Follow-up observations by Melis and colleagues have confirmed their initial findings.

What was once one of the brightest discs in the sky had disappeared in less than two years. Nothing like this has been seen before and scientists have no theories to explain it.

"The discovery has just blown my mind," says Melis.

"We struggled with that for quite some time trying to convince ourselves that there's nothing wrong with our data.

"There's no evidence that the star is changing and there's nothing that could have blocked out the light from the dust ring without also blocking out the star itself."

Writing in the journal Nature, Melis and colleagues have proposed two hypotheses which they say fit the short time scale for the disc's sudden disappearance.

The first involves the dust particles becoming small enough to be blown out of the disc by light pressure from the star.

Alternatively, surrounding gas in the disc may have slowed the dust particles' orbital speed, causing them to spiral into the star.

"I'm not saying that either scenario actually occurred," says Melis.

"We really need more evidence. We're going to keep monitoring the system to see what, if anything, changes.

"Anything that happens now will be a clue as to what's going on, even if it's nothing."