Scientists Discover Unexpectedly Cold Planet-Forming Flying Saucer Disk

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Astronomers in France have discovered a protoplanetary disk surrounding a young star about 400 light years away from Earth. Dubbed the Flying Saucer, the disk’s building blocks are so cold that they may force scientists to rethink the current models of how planets form. Usually planetary disks form at various angles with respect to the sun. But this stellar body appears edge-on from Earth, earning it the nickname Flying Saucer.

Astronomers measure the dust grains of the Flying Saucer

Its host star 2MASS J16281370-2431391 is located in the Rho Ophiuchi star formation region. Astronomers were able to make direct measurements of large dust grains in the protoplanetary disk. Stéphane Guilloteau of the Laboratoire d’Astrophysique de Bordeaux in France said in a statement that the disk could not be observed against a black and empty night sky. Instead, it is visible in silhouette in front of the glow of the  Rho Ophiuchi Nebula. Parts of the disk are colder than the background, said Guilloteau.

Astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and the IRAM 30-meter telescope in Spain to study the disk. The Flying Saucer is located about 9 billion miles from the star. Scientists found that temperatures in the disk were -266 degrees Celsius, just 7 degrees Celsius above absolute zero. As the system matures, these dust grains will form planets.

Dust temperature affects the size and characteristics of planets

However, the existing models of planetary formation suggest that the disk must be between -258 and -253 degrees Celsius, or 10-15 degrees above absolute zero, to form planets. Although still cold, the discrepancy is huge in models of planet formation. It may prompt astronomers to rethink how planets form within protoplanetary disks surrounding newborn stars.

Emmanuel di Folco, the co-author of the study, said they need to find out what dust properties could result in such low temperatures. One possibility is that temperature may depend on the grain size, with larger grains being cooler than their smaller siblings. The dust temperature in planetary disks has a significant impact on the developmental characteristics and size of planets that eventually form.

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