For the first time, scientists studying Neptune have been able to track the blossoming of a ‘Great Dark Spot’ — an enormous, whirling storm in the planet’s atmosphere.

Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and her colleagues have used the Hubble Space Telescope to photograph Neptune each year since 2015. In late 2018, the researchers spotted a dark blob nearly the size of Earth drifting westwards in Neptune’s northern hemisphere. It is the sixth such blob ever seen on Neptune, and represents a vortex of churning winds.

Bright white ice clouds had appeared in the same region two to three years earlier. Computer simulations link the clouds’ brightness with the depth of the storm that followed, and suggest that the 2018 dark spot extended deep into the atmosphere.

The results might aid researchers’ understanding of Jupiter’s centuries-old Great Red Spot and other circulation patterns in the atmospheres of giant planets.