The general rule of thumb for telescopes is the darker the better. But time on the world’s high-powered observatories is precious, so University of California Berkeley grad student Ned Molter was tasked with testing whether it’s possible to study bright objects during the twilight hours as well as at night. It turns out, it is indeed possible. And during one of these tests, Molter and his team discovered a new storm system nearly the size of Earth swirling in the atmosphere near Neptune's equator.
Spanning nearly 5,600 miles across, this equatorial behemoth is unusual for the big blue planet. Though astronomers have watched large, bright storm systems develop and dissipate in Neptune's atmosphere for decades, most of those large storms tend to develop near the planet’s poles—not its equator.
So far, this latest storm has also stuck around, reports Nadia Drake for National Geographic. Molter first spotted the storm on June 26, watching it grow brighter between then and July 2. As of July 25, the storm was still visible, reports Drake.
Neptune has some of the worst weather in the solar system, with winds that whip up to 1,500 miles per hour and average temperatures hovering around -353 Fahrenheit. According to a press release, in 1989, the Voyager 2 spacecraft imaged a giant storm on Neptune dubbed the Great Dark Spot. By the time the Hubble Space Telescope took a peek in 1994, that storm had dissipated, but the space eye did find a series of storms dubbed the Northern Cloud Complex. When they first got a glimpse of the new storm, Molter and his adviser Imke de Pater, initially thought they might be observing those older systems, reports Drake, but the measurements did not line up.
There are a couple possibilities for the origin of the storm, according to the press release. One is that it is an upper atmosphere disturbance that could fizzle out relatively quickly. The other is that the bright clouds of the mega-storm are connected to a deep (and dark-colored) vortex that is sucking up gases closer to the planet’s surface. As the gases rise up they cool, condensing into the bright methane clouds.
As Maddie Stone at Gizmodo reports, this newest storm is composed of bright splotches, but scientists don't yet know if these are clouds floating out of a dark vortex, which is unusual at the equator where it is difficult to sustain such strongly swirling storms. “It could be that the underlying vortex is a few degrees north or south of the equator, or that this cloud lacks an underlying vortex and will quickly shear apart,” Molter tells Stone.
Understanding ice giants like Neptune and Uranus is taking on new importance. In June, data from the Kepler planet-hunting space telescope revealed that miniature versions of Neptune are some of the most common types of planets in our galaxy.
Understanding our icy neighbors will give researchers insights into far-flung planetary systems. Just in the last few months support for new missions to explore the two planets has gained steam, with NASA releasing proposals for missions to the planets in June. So far, Voyager 2 is the only mission to reach the planets, conducting flybys of Uranus in 1986 and getting a closer glimpse of Neptune in 1989.