Methane colors the skies of Neptune blue, fills lakes on Saturn’s moon Titan, and powers homes and businesses here on Earth. And it could someday provide evidence of life on planets in other star systems. Methane is a fairly simple organic molecule. Here on Earth, it’s produced by the decomposition of dead plants, and in the digestive tracts of cattle and other animals. It can also be extracted from coal. Methane is the main ingredient in natural gas, which provides more than a quarter of American electricity. It’s also a powerful greenhouse gas, so any that escapes into the air enhances global warming. Methane is common in the atmospheres of the planets Uranus and Neptune. It absorbs red wavelengths of light, so it makes Neptune look blue, and Uranus blue-green. It’s also common on Titan, the largest moon of Saturn. Temperatures are so cold there that the methane is in liquid form, so it fills the role that water fills here on Earth. Along with ethane, it forms clouds and rain, and fi
