Saturn's E ring consists of particles so small that they would be dispersed by solar radiation pressure in a few tens of thousands of years. That the ring exists today suggests, therefore, that it originated in the relatively recent past—but how? Researchers suggest that Enceladus, one of Saturn's moons, may be responsible. This icy moon has no craters, possibly because liquid water from its interior flowed across the surface in the relatively recent past, erasing all preexisting impact features. An impact into Enceladus within the past thousand years or so may have blasted liquid water into space. Water droplets would have frozen quickly into ice crystals, which may then have drifted through the Saturnian system and formed into the E ring.

Which of the following, if true, would challenge the hypothesis presented in the passage concerning Enceladus and Saturn's E ring?

❑ Enceladus is not the only moon orbiting Saturn.
❑ Enceladus's lack of craters is not due to erasure by water.
❑ No impact has occurred on Enceladus in the past few tens of thousands of years.



Select the sentence that points out the significance of the fact that the particles that make up Saturn's E ring are susceptible to dispersion.