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2018-09-28. Cosmic conundrum: The disks of gas and dust that supposedly form planets don’t seem to have the goods.

posted Sep 29, 2018, 9:21 PM by Alan Gould
By Adam Mann, Science Magazine. [https://www.sciencemag.org/news/2018/09/cosmic-conundrum-disks-gas-and-dust-supposedly-form-planets-don-t-seem-have-goods] For GSS A Changing Cosmos chapter 7. Excerpt: Astronomers have a problem on their hands: How can you make planets if you don’t have enough of the building blocks? A new study finds that protoplanetary disks—the envelopes of dust and gas around young stars that give rise to planets—seem to contain orders of magnitude too little material to produce the planets. “This work is telling us that we really have to rethink our planetary formation theories,” says astronomer Gijs Mulders of the University of Chicago in Illinois, who was not involved in the research. ...The brightness of radio waves emitted by dust in the disk can be used to give a reasonable estimate of its overall mass. ...In the new study, astronomers led by Carlo Manara of the European Southern Observatory in Munich, Germany, used [Atacama Large Millimeter Array (ALMA)] to compare the masses of protoplanetary disks around young stars between 1 million and 3 million years old to the masses of confirmed exoplanets and exoplanetary systems around older stars of equivalent size. The disk masses were often much less than the total exoplanet mass—sometimes 10 or 100 times lower, the team will report in an upcoming paper in Astronomy & Astrophysics. ...a great deal of mass, perhaps as much as 10 times what’s been observed, could be hidden in the form of pebbles, which are slightly too big to show up in such investigations....