The Great Red Spot has been a fixture in Jupiter’s clouds for at least 350 years. Maybe longer. The huge spot is still ‘Great,’ but not as great as it once was. The famous storm is getting smaller.

When Voyager 1 and Voyager 2 cruised past Jupiter in 1979, the Great Red Spot measured 14,500 miles across. In 1995, the Hubble Space Telescope estimated the storm was 13,020 miles across. A 2009 photo showed the shrinking continue with the storm measuring 11,130 miles across. By 2012, amateur observations showed the shrinking accelerating to a pace of 580 miles per year.

In 2014, the Great Red Spot measured just 10,250 miles across. Here’s what NASA’s Amy Simon had to say at the time. “In our new observations it is apparent very small eddies are feeding into the storm,” said Simon. “We hypothesized these may be responsible for the accelerated change by altering the internal dynamics and energy of the Great Red Spot.”

Today, NASA’s Juno spacecraft will fly directly over the solar system’s most famous storm. At 10:06 pm ET, Juno will be 5,600 miles above the swirling vortex of clouds making up the Great Red Spot. Every instrument and JunoCam will be trained on the storm system.

Juno’s instruments will look through the top cloud layer and see how far this storm goes. What drives it? What local conditions create the unique storm? The data collected tonight will give scientists their best look yet at the Great Red Spot.

Data is great and all, but when are we getting the first pictures? We don’t have an exact time frame yet. First, Juno has to complete its up-close look at Jupiter. After that, the spacecraft will downlink the data back to Earth. You can watch that happen in real-time over at Deep Space Network Now.

We do have a general idea of what the pictures will look like. Candy Hansen, Juno’s co-investigator, jumped on the Unmanned Spaceflight forums to tell us what to expect.

“We have scheduled 3 GRS images – one that will capture the northern edge, one centered as Juno is right over the GRS, and one looking from the south. The third one will include the methane filter.”

Also, image processing is a little different with this mission. The Juno team looks to the public for help. And the results are stunning. Here’s one recent image processed by Gerald Eichstädt.

Jupiter clouds

Credit: NASA / SwRI / MSSS / Gerald Eichstädt / Seán Doran

And another from Björn Jónsson.

Jupiter in true color

Credit: NASA / JPL-Caltech / SWRI / MSSS / Björn Jónsson

With all the excitement surrounding the Great Red Spot flyby, we won’t be waiting long to see the first breathtaking up-close image. Juno has traveled more than six years in space for tonight’s moment above the Great Red Spot.

“The success of science collection at Jupiter is a testament to the dedication, creativity and technical abilities of the NASA-Juno team,” said Juno project manager Rick Nybakken recently. “Each new orbit brings us closer to the heart of Jupiter’s radiation belt, but so far the spacecraft has weathered the storm of electrons surrounding Jupiter better than we could have ever imagined.”

Juno will continue diving perilously close to Jupiter until February 2018. Then, it will fly one final time above Jupiter’s clouds before slamming into the thick atmosphere and burning up.

I’ll keep this post updated as we hear more from the Juno team.


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