The reason why the presence of dusty disks were surprising is because; A) such systems could not have formed planets.
A dusty disk is a circumstellar disk of dust and debris found in the orbit around a star and sometimes these disks contain prominent rings.
Now, these disks around young stars are made up of 99% gas and 1% dust and this small amount of dust is still sufficient to make the disks opaque and dark at visible wavelengths.
Now, the dust may be 1% but it is 1 million times more than that found in our solar planets and it orbits at a distance from the star that is similar to the orbits of Earth and Venus around our own Sun.
The missing options are;
A) such systems could not have formed planets.
B) their composition differs so much from their stars.
C) their instruments were not thought to be powerful enough to make such a measurement.
D) gas and dust should be rapidly ejected into space by the radiation from a hot star.
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