The water wakes left by ocean tankers and container ships don't last long, but large vessels also leave an airborne trail.

In July, the cloudy signatures of passing ships spelled out the letter A above the Pacific waters off the coast of northeast Russia. NASA's Aqua satellite was passing overhead and captured the alphabetical phenomenon.

On Sunday, NASA's Earth Observatory shared the image online.

It's an intriguing image, and some viewers may wonder: how do passing ships generate clouds?

Phytoplankton can help explain.

Previous studies have identified connections between clouds and phytoplankton, the tiny, drifting algae-like organisms that populate the world's oceans.

One NASA study used satellite data and marine biology models to show phytoplankton "produce airborne gases and organic matter to seed cloud droplets, which lead to brighter clouds that reflect more sunlight."

In the same way water vapor clings to biologically-seeded aerosols -- sourced from plankton-packet ocean spray -- clouds can form around pollution particles emitted by large ships. The narrow clouds form in long strips tracing the paths of ships.