NASA's Juno spacecraft has been making repeated swoops just above the cloud tops of Jupiter. During the latest fly-by, on Monday, the spacecraft passed about 9000 kilometres above the Great Red Spot, a 16,000-kilometre-wide storm that has swirled for at least 350 years. NASA posted images from the fly-by on the web on Wednesday.

Amy Simon, a scientist at NASA's Goddard Space Flight Centre in Greenbelt, Maryland, who studies planetary atmospheres, said the appearance of the spot may have changed since the end of NASA's Galileo orbiter mission more than a decade ago.

"I would say the internal clouds look less sheared apart in some places, compared with Galileo," she said.

"We expected that, based on recent Hubble imaging, but these images are a higher-resolution view of those clouds and exactly how they've changed over the past decades."

The released images look distorted.

"The hourglass shape is because we are so close and the horizon is foreshortened," said Candice Hansen-Koharcheck, NASA's lead investigator for the JunoCam instrument.

Juno's images are part of the mission's outreach to the public, inviting "citizen scientists" to download the pictures for tweaking and enhancing.

Hansen-Koharcheck pointed to one processed image submitted as part of the crowdsourced analysis effort.

Adjustments put the view back into the proper, undistorted perspective and added a more vivid palette.

"The detail is terrific," she said.

James O'Donoghue, another scientist at NASA Goddard, said: "The more we zoom into the Great Red Spot, the more turbulent it seems to be.

"In some of the processed images, we can clearly see anti-clockwise rotating cells within the giant storm itself - storms within storms."

Detailed study will come later. Scientists will use Juno's other instruments to gather clues about what drives the storm and how far down into the atmosphere it descends.

O'Donoghue is studying temperatures in the upper atmosphere using an instrument known as the Jovian Infrared Auroral Mapper. In a paper published last year, he and colleagues used similar data from ground-based telescopes to study why the region above the Great Red Spot storm was unexpectedly hot.

They suggested that the heat originated from below as the storm's turbulence rose in the form of soundlike waves that crashed at higher altitudes where the atmosphere was too thin for the waves to propagate. The crashing waves heat the upper atmosphere, the scientists said.

Juno's observations should pinpoint spatial variations in the infrared emissions, and the scientists could then check whether turbulent regions seen in the JunoCam images coincide with hot spots in the atmosphere.

"Such a finding would be a spectacular confirmation," O'Donoghue said.

Scott J. Bolton, Juno's principal investigator, was also enthralled by the pictures.

"Nature is incredible," he said in an email statement released by NASA.

"This storm is so powerful and so beautiful. I can't wait to see what's underneath."

The New York Times