Saturn’s largest moon is Titan. NASA’s Cassini spacecraft detected evidence of a methane rainstorm at low altitudes on it. The Cassini observations suggest the conditions that led to the rainfall observed on Titan are similar to tropical weather patterns on Earth. The difference is, methane is substituted for water. Last spring, Cassini observed a storm around Titan’s equator, and a month later, clouds were detected. Subsequent months revealed images of a darker surface. Scientists believe this is due to the moon’s surface becoming saturated following the methane rainstorm. Geophysical Research Letters reports atmospheric circulations are affected by solar illumination as Titan is the only moon in the solar system with a developed atmosphere. Methane clouds form on Titan as moisture clouds form on Earth.

Fastcast: A shower.

A 40 percent chance of storms. Partly cloudy, high near 89. Easterly winds 5 mph. Tonight: 30 percent chance of rain before 1 a.m. Low about 69. Easterly winds 5 mph.