The Great Red Spot is shrinking.

There is no question that the solar system’s most famous storm is considerably smaller than it was 40 years ago. When the Voyager spacecraft flew by Jupiter in the late 1970s, the Great Red Spot was large enough to hold three Earths. Today, it could only hold about one Earth. And if one were to reach back over a century, images of the red spot suggest that it was staggering in size.

“If you look at pictures from the late 19th century, you’d swear it was the great red sausage,” Glenn Orton, a planetary scientist at NASA’s Jet Propulsion Laboratory, tells Inverse. The storm might once have stretched across 30 degrees of latitude, nearly a tenth of the gas giant’s circumference.

It remains uncertain, however, how great the Great Red Spot really was back then, or how old it is. Precise records have only been kept since the 1970s, although telescope-users spotted the storm over 150 years ago.

“The history of the thing is spotty — no pun,” says Orton. “It was only until after 1855 when people started saying they saw something.”

That the storm now appears to be shrinking makes little sense, as it should gain more girth and power by continually gobbling up other storms around it. Last week, the NASA space probe Juno stared directly down into Jupiter’s crimson cyclone for some 12 minutes. It’s our closest-ever view of Jupiter’s Great Red Spot, and it might give scientists some insight into why it’s diminishing.

A close-up processed image of Juno's recent (also close) flyby, which brought the space probe 5,600 miles above the storm. The darker areas are deeper portions of the storm, says NASA's Glenn Orton.

Three years ago, some NASA scientists proposed that collisions with other storms might be responsible for the historic storm’s undoing by sapping it of energy.

“Our original hypothesis was about small counter-rotating eddies perhaps opposing the Great Red Spot’s momentum, effectively taking energy from it,” wrote Amy Simon, a senior scientist for planetary atmospheres research at NASA’s Goddard Space Flight Center, in an e-mail to Inverse.

But after reviewing images of the spot from the powerful Hubble Space Telescope, Simon and her team found that the nearby eddies were not draining the Great Red Spot. In fact, the storm continues to consume many of these smaller storms.

“It’s ingesting smaller vortices — think of the Great Red Spot as a vampire eating smaller storms,” says Orton. He also recommended Pac-Man as a metaphor but wasn’t sure how many people these days are familiar with the ravenous, yellow arcade creature.

A view of Jupiter and the Great Red Spot from the near infrared-viewing Gemini North telescope, The lighter areas, notably the Great Red Spot, signify high altitude clouds. NASA researchers will use infrared imaging of the storm -- in concert with other images -- to try and understand why it's shrinking.

For now, “it remains an open question,” says Orton. He suggests that although the Great Red Spot is still consuming storms, there might not be as many storms around to eat. Or the storms might not be spinning as rapidly, so they don’t provide the great crimson spot with the energy it needs to sustain itself.

The solar system’s great tempest, then, eats and eats but continues to shrink. Both Simon and Orton plan to assess the latest Juno images, as well as infrared images from other telescopes and data from Hubble (which has been watching Jupiter for decades) to give them a complete picture of the storm’s depth, temperatures, and speed. The sum of the data may clarify the storm’s mystifying behavior.

Juno stared deeply into the eye of the storm last week, but the detailed, swirling images sent back to Earth didn’t answer many questions. In fact, it created more. The center of the storm, similar to the empty eye in one of Earth’s hurricanes, is filled with clouds, but these clouds aren’t spinning. “Winds in the middle of the spot are almost zero,” says Orton, and scientists don’t understand why.

This is a weird phenomenon but a fitting feature for a strange, inexplicably shrinking storm on a gas giant whose thick bands of swirling clouds have sometimes baffled scientists. Upon seeing some of Juno’s first images depicting storms in the south pole colliding with one another, like bumper cars, Scott Bolton, principal investigator of the Juno mission, said this: “There is so much going on here that we didn’t expect that we have had to take a step back and begin to rethink of this as a whole new Jupiter.”

If the Great Red Spot isn’t just in a shrinking phase, but actually in the process of dying, this might disappoint global astronomers, scientists, and people generally, but Orton wouldn’t be too surprised.

“Nothing lasts forever,” he says.

In the late 1970s, three Earths could have fit into Jupiter's Great Red Spot. NASA scientist Glenn Orton says that about 1.3 Earths can fit inside today.