In yet another interesting presentation from AGU’s Fall Meeting, scientists used the Hubble Space Telescope to image and track a storm on the surface of Neptune. The farthest gas giant has giant storms just as Jupiter does, but it turns out that Neptune’s storms don’t last nearly as long. In fact, they tend to disappear after a couple of years. And the only reason we know this is because we’ve been able to use Hubble to take images of Neptune. Otherwise, a lot of people would think the Great Dark Spot seen by Voyager 2 back in 1989 was still around.

It’s not. Since Hubble went up, it has seen four such storms come and go. Until now. This latest storm did something unusual. Not only is it still there, but it has actually reversed direction and possibly spun off a remnant.

The current storm was first observed in Neptune’s northern hemisphere back in 2018. This year is the two-year mark, which meant new images should have shown the storm dissipating. Basically, storms on Neptune drift toward the equator over time, where the Coriolis effect — the forces that make storms rotate, like hurricanes — is much weaker. Storms are unable to remain coherent, and they break apart and disappear.

However, what scientists found in August of this year was that the storm, which had been seen making its advance toward the equator, was now making its way back north again. Not only that, there was a smaller dark storm that was now moving away from the original storm. No one is certain that the small storm spun off from the bigger one, but it does match some simulations that show a similar type of disruption.

And here is where the telescope time becomes important. It’s not easy to get telescope time. There are proposals and scheduling and targets and considerations of what lines of research are more pressing than others. The pictures taken by Hubble for this study are a part of the Outer Planet Atmospheres Legacy (OPAL) program, led by Amy Simon at NASA Goddard. This program takes annual pictures of the outer planets that allow us to map their surfaces on a regular basis and allows researchers to catch fleeting events they would not see otherwise.

As Simon said: We wouldn’t know anything about these latest dark spots if it wasn’t for Hubble. We can now follow the large storm for years and watch its complete life cycle. If we didn’t have Hubble… we wouldn’t have known about the four other spots Hubble discovered.

Hubble is a gem. Thirty years in, and we are still making discoveries and advances in our understanding of our solar system based on the images it takes.

More Information

Hubble Space Telescope press release