NASA puzzles over what colours Jupiter’s Great Red Spot

NASA’s Planetary Atmospheres and Outer Planets programs are funding new research into Jupiter’s mysterious Great Red Spot – a gigantic storm wider than the diameter of Earth that has been raging with winds up to 650 km/h mph for at least 150 and maybe 400 years.

The results are due to be published later this year.

One of the researchers, Amy Simon, an expert in planetary atmospheres at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said learning more about Jupiter and its Great Red Spot could help scientists understand Earth’s weather system better.

Jupiter’s weather functions under the same physics as Earth, she said, just millions of kilometres farther from the Sun.

Simon also said Jupiter studies could improve our understandings of worlds beyond our solar system. “If you just look at reflected light from an extrasolar planet, you’re not going to be able to tell what it’s made of,” Simon said. “Looking at as many possible different cases in our own solar system could enable us to then apply that knowledge to extrasolar planets.”

But scientists are still struggling to understand what causes the swirls of colour in the storm and they are not even sure if it is a continuous storm lasting centuries or a string of similar storms. 

While people saw a big spot in Jupiter as early as they started stargazing through telescopes in the 1600s, it is still unclear whether they were looking at a different storm. Today, scientists know the Great Red Spot is there and it’s been there for a while, but they still struggle to learn what causes its swirl of reddish hues.

Creating even further confusion about the duration of the storm, recent observations suggest the storm is decreasing in size (see the Cosmos story Jupiter’s shrinking red spot).

Scientists believe Jupiter’s upper atmosphere has clouds consisting of ammonia, ammonium hydrosulfide, and water, but they don’t know exactly how or even whether these chemicals react to give colours like those in the Great Red Spot.

“We’re talking about something that only makes up a really tiny portion of the atmosphere,” Simon said. “That’s what makes it so hard to figure out exactly what makes the colours that we see.”

Simon and colleagues Mark Loeffler and Reggie Hudson have been performing laboratory studies to investigate whether cosmic rays can chemically alter ammonium hydrosulfide to produce new compounds that could explain the spot’s colour.

But the colouring may result from multiple factors, as opposed to just ammonium hydrosulfide.

“Ideally, what you’d want is a mixture with the right components of everything that you see in Jupiter’s atmosphere at the right temperature, and then irradiate it at the right levels,” Simon said.

Ultimately, Simon and Loeffler said solving the Great Red Spot’s mystery will take more experiments combining chemicals under the right temperatures, light exposures and radiation doses. “What we are trying to do is design lab experiments more realistic to Jupiter’s atmosphere,” Simon said.  

NASA has more facts and figures on Jupiter here.