News from Jupiter: How our understanding has deepened

NASA’s Juno spacecraft is deepening our understanding of the solar system’s largest planet, with findings that suggest its swirling weather patterns continue 1,900 miles into the atmosphere. The planet is about 89,000 miles across at the equator, so we now know that leaves a core below the weather of more than 85,000 miles in diameter.

Launched from Cape Canaveral, Florida, in 2011, Juno reached Jupiter in 2016. Between then and March 7, when the latest discoveries were announced, it had carried out 10 complete orbits covering 122 million miles. At its closest, the probe reaches to within 2,200 miles of the cloud tops — which look, according to some of the nearest photos, like swirls of colored whipped cream.

Jupiter is something like a protostar that never ignited, almost 90 percent hydrogen and 10 percent helium with "a sprinkle of all the other elements." Its lightning is 100 times as bright as our little planet's. Speaking of size, Jupiter encompasses 70 percent of the solar system's planetary material. Below a certain level — the new study suggests that is almost 2,000 miles under the cloud tops — the gigantic interior is a ball of liquid metallic hydrogen. Vast pressure at depth has "squeezed" all the electrons off the hydrogen atoms, with the remnant reacting like a metal, according to NASA.

Four papers analyzing the latest discoveries were published March 7 by the scientific journal Nature. To summarize the papers' abstracts (which are themselves summaries), researchers found:

• Jupiter's jet streams, which can be tracked through Earth-based telescopes because of the cloud movements, "extend down to depths of thousands of kilometres (British spelling for kilometers) beneath the cloud level, probably to the region of magnetic dissipation at a depth of about 3,000 kilometres" or 1,900 miles. Findings about the varying gravity allowed scientists to make the estimates. The results mean that about 1 percent of Jupiter's mass is involved in atmospheric dynamics, as compared with Earth's 0.0001 percent.

• As Juno swept above the cloud tops, it sensed that Jupiter's gravity wasn't pulling on it evenly, but changed; the gravitational field is not symmetrical. The lack of symmetry is "attributed to differential rotation and deep atmospheric flows." The paper adds, "We find a north-south asymmetry, which is a signature of atmospheric and interior flows."

• Although the cloud zones rotate at different rates — the differential is up to nearly 225 miles per hour — until now nobody knew whether the interior rotated as a unit. The new studies show that "the deep interior of the planet rotates nearly as a rigid body, with differential rotation decreasing by at least an order of magnitude compared to the atmosphere." Deep down, magnetic drag from the liquid metal hydrogen apparently overpowers the atmosphere's rotation.

• Jupiter is side-on to Earth, so telescopes here can't study the poles with precision, and earlier probes passed by the planet's central region. For the first time, the Juno project cruises above the poles, sending us startling discoveries about wind patterns there. Clusters of long-lasting cyclones surround both. The circulation forms persistent patterns of large polygons, says the report. "In the north, eight circumpolar cyclones are observed about a single polar cyclone; in the south, one polar cyclone is encircled by five circumpolar cyclones." Why cyclones around each pole don't merge, and how they formed, "are unknown."

Alberto Adriani, Rome, lead author of the polar paper, said in missionjuno.swri.edu, "Each one of the northern cyclones is almost as wide as the distance between Naples, Italy, and New York City — and the southern ones are even larger than that. They have very violent winds, reaching, in some cases, speeds as great as 220 mph (350 kph). Finally, and perhaps most remarkably, they are very close together and enduring. There is nothing else like it that we know of in the solar system."

On a side note: The Juno project costs American taxpayers $1.13 billion, according to jpl.nasa.go. It's a worthy scientific endeavor, a bargain at twice the price. Ideally, any citizen should be able to read the scientific results in full, at no additional charge, as soon as finalized. The space agency refers readers to Nature's website, where only the abstracts are available free. To read the full report, one must subscribe to Nature at $199. This is hugely unfair to the project's sponsors, all of us.

Scott Bolton, principal investigator of the Juno project, called the results astonishing. He said they show that Jupiter has turned out to be different from predictions. They testify "to the value of exploring the unknown from a new perspective with next-generation instruments," he said on missionjuno.swri.edu.

Juno has finished its 11th cruise past the poles. Its planned career is only about one-third over. Before it "deorbits" into the planet, it will have circled it 33 times. Earthlings await further discoveries.

Joe Bauman writes an astronomy blog at the-nightly-news.com and is an avid amateur astronomer. His email is joe@the-nightly-news.com.