The amount of previtamin D2 and photoproducts produced during sun exposure could also have been a photochemical signal (actinometer) to tell the organism that it has been exposed to enough solar UVB radiation and to signal it to leave the surface into deeper water where it would no longer be exposed to UVB radiation due to the ocean's ability to absorb this solar energy.
Also, some characteristics of its surface and history (such as its distance from the Sun, which weakened solar radiation enough to allow some fairly low-freezing-point components to be incorporated during its formation), point to the presence of volatile materials in the interior of Ceres.
Although the question remains open, the conjectures vary from a passing star scenario to grinding of smaller objects, via collisions, into dust small enough to be affected by solar radiation.
When the availability of solar radiation is not enough to develop experimental investigation in the field of concentrating solar energy, solar simulators are a widely employed solution.
You and I are stuck with a subjective, emotion-based risk perception system that mostly works to keep us safe, but sometimes leads us to worry about some things too much (radiation, 'chemicals') and some things not enough (climate change, skin cancer from solar radiation).
Gamma rays from a supernova would induce a chemical reaction in the upper atmosphere converting molecular nitrogen into nitrogen oxides, depleting the ozone layer enough to expose the surface to harmful solar radiation.
Solar radiation passes through to the earth readily enough, but the heat radiated by the earth is at least partly held back.
When solar radiation shines onto the material, electrons can absorb enough energy to jump from the valance band to the conduction band, leaving behind vacancies called holes.
Efficient photocatalytic materials should not only be able to exploit solar radiation to produce electron hole pairs, but also ensure enough charge separation to allow electron transfer reactions, leading to solar energy driven thermodynamically up-hill processes.
