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"upstart" writes:

Cosmic conundrum: The disks of gas and dust that supposedly form planets don't seem to have the goods

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.

Stars are born from colossal clouds of gas and dust and, in their earliest stages, are surrounded by a thin disk of material. Dust grains within this halo collide, sometimes sticking together. The clumps build up into planetary cores, which are big enough to gravitationally attract additional dust and gas, eventually forming planets.

But many details about this process remain unknown, such as just how quickly planets arise from the disk, and how efficient they are in capturing material. The disks, surrounded by an obscuring haze of gas and dust, are difficult to observe. But radio telescopes can penetrate the haze and investigate young stars. The brightness of radio waves emitted by dust in the disk can be used to give a reasonable estimate of its overall mass.

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