Simplify the following text for a Grade 9 native English-speaking person.
Original: Its purpose is unknown , but it may be useful in absorbing ultraviolet rays to manufacture vitamin D , as well as to determine light\/dark cycles , and help with thermoregulation .
Simplified: The function of the parietal eye is unknown , but it may be useful in absorbing ultraviolet rays to manufacture vitamin D. It may also do other things .