At first blush, Titan seems an inhospitable place for an active biosphere. Its opaque nitrogen-methane cocoon is the second-densest atmosphere among all the solid bodies of the solar system, after Venus. Its atmospheric blanket sustains surface temperatures of –290 degrees Fahrenheit (–178 degrees Celsius). Still, these chilly temperatures are much warmer than the moon’s smaller sibling Enceladus, whose daytime temperatures hover nearly 80 F (27 C) below Titan’s. Yet despite such frigid temperatures, Titan has other features that might make it more conducive to life.

Titan experiences rainfall. But instead of water, Titan’s clouds dump liquid methane, which is chemically similar to the natural gas that many of us heat our homes with. No matter what the rain is made of, the great moon is the only world besides Earth confirmed to have an active rain cycle fed by evaporation from surface lakes and rivers. Its river valleys drain into liquid-filled basins, some as large as the terrestrial seas. Titan’s largest sea, Kraken Mare, covers about 154,000 square miles (400,000 square kilometers), making it roughly five times the area of North America’s Lake Superior, or nearly the size of Asia’s Black Sea.

A second kind of precipitation may have even more bearing on the search for life on Titan: a steady drizzle of hydrocarbons. This organic “soot” combines with methane to form complex compounds, the raw materials of life. Titan’s winds pile up the hydrocarbon fallout into vast sand seas.

But methane and hydrocarbons aren’t the only things falling from Titan’s soupy skies. Sunlight and radiation from Saturn break up nitrogen and methane molecules in Titan’s atmosphere. When these fragments recombine, they create a compound called vinyl cyanide. Vinyl cyanide is important in the search for life because it tends to assemble into membranes like those found in terrestrial living cells.

This news has exciting implications for life on Titan, but it was a long time coming. Over a decade ago, the Cassini spacecraft detected the building blocks of vinyl cyanide on the distant moon, yet it was not equipped to confirm its existence. Later, in 2014, astronomers calibrating the 66 antennas of the Atacama Large Millimeter/submillimeter Array in Chile happened to use Titan as their target. As luck would have it, their data contained the fingerprints of vinyl cyanide. We now know that thousands of tons of the stuff float high in Titan’s upper atmosphere, and an astounding 10 billion tons may have accrued in Titan’s largest methane seas, Ligeia Mare and Kraken Mare.