Frigid 'Flying Saucer' May Change What we Know about Planets and Their Formation

The frigid "flying saucer" may change what we know about planets. Scientists have measured the temperature of large dust grains around the young star 2MASS J16281370-2431391 and have found a bit more about discs of gas and dust.

In this latest study, the researchers used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the glow coming from carbon monoxide molecules in the young star's disc, which is nicknamed the Flying Saucer. That's when the researchers noticed that in some cases they saw a negative signal. Normally, a negative signal is physically impossible. In this case, though, the researchers had an explanation.

"This disc is not observed against a black and empty night sky," said Stephane Guilloteau, one of the researchers, in a news release. "Instead it's seen in silhouette in front of the glow of the Rho Ophiuchi Nebula. This diffuse glow is too extended to be detected by ALMA, but the disc absorbs it. The resulting negative signal means that parts of the disc are colder than the background. The Earth is quite literally in the shadow of the Flying Saucer!"

The researchers then derived a disc dust grain temperature that was only 7 degrees above absolute zero. It was the first direct measurement of the temperature of large grains in such objects, and was much lower than the 15 to 20 Kelvin that most current models predict.

"To work out the impact of this discovery on disc structure, we have to find what plausible dust properties can result in such low temperatures," said Emmanuel di Folco, one of the researchers. "We have a few ideas-for example the temperature may depend on grain size, with the bigger grains cooler than the smaller ones. But it is too early to be sure."

Further observations are needed, but the cooler dust may just have significant consequences for the understanding of protoplanetary discs.

The findings are published in the journal Astronomy & Astrophysics.

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