Uranus might have ammonia clumps in its atmosphere Buradaki/Alamy
Neptune and Uranus may have mushballs, which are slushy hailstones that hide deep within them. These ammonia-rich clumps may be the reason why ammonia is low in the atmospheres of the ice giants.
Based on other compounds measurements, Uranus, Neptune, and other giant planets seem to have surprisingly low levels of ammonia. However, the vast majority of giant planets in the solar system should have the same amount. These two planets could have formed by some other process.