Guilloteau's team carried out the first ever direct measurements of the relatively large grains of dust in the Flying Saucer (measuring approximately one millimeter across), located around 15 billion kilometers (9 billion miles) from the star and found they had settled to a low temperature of -266 degrees Celsius - that's only 7 degrees above absolute zero. These grains will eventually go on to form planets as the system matures, but current theoretical models predict this dust should be at least 10 to 15 degrees (−258 to −253 degrees Celsius) above absolute zero. Although still cold, in the field of planetary formation models, this discrepancy is huge.
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"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 co-author Emmanuel di Folco, also of Laboratoire d'Astrophysique de Bordeaux. "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."
This may sound like a minor complication in the field of planetary science, but the temperature of the dust in protoplanetary disks can greatly impact the size and developmental characteristics of the planets that eventually form. Cooler dust, for example, could allow larger planets to coalesce closer to their parent star in compact protoplanetary disks.
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Now we need more studies of more protoplanetary disks to see if this temperature versus particle size trend is typical for planet-forming systems, hopefully adding more detail to planet formation models.