Round “anderound anderound”
The JUNO Mission
In the Roman pantheon, the god Jupiter stands above all. As the protector of Rome, he ruled over law and social order with thunder and lightning. So it is appropriate that the largest planet in our Solar System be named Jupiter.
About 1,300 Earths can fit into its volume. It is 320 times more massive than the Earth and contains about 2.5 times the mass of all the other planets combined. Yet, because it is mostly gas, it is about 4 times less dense than the Earth.
Jupiter is 5.2 Astronomical Units from the Sun (for reference, the Earth is 1 AU). Sunlight takes about 43 minutes to reach its surface (compared to 8 minutes for Earth). Sunlight reaching Jupiter is about 27 times weaker than on Earth (consistent with the inverse square law; 1/(5.2)2). Its linear orbital speed is 23,000 miles per hour (Earth moves 3 times faster) and takes 12 years to complete an orbit. Yet, it has the shortest day in the Solar System: 10 hours for one complete rotation.
Since the Pioneer mission of 1972, Jupiter has been the subject of numerous probes. See ESA Science & Technology – Missions to Jupiter for more information. Their findings revealed a planet with a turbulent gaseous surface (hydrogen and helium), marked by storms larger than the Earth and explosive lightning strikes. It possesses an enormous magnetic field generated by its vast underground sea of metallic hydrogen. For more details on Jupiter’s composition, see the following article: 11.2: Jupiter’s Interior – Physics LibreTexts.
These missions also helped us realize that Jupiter’s large gravitational field can be both a blessing and a curse. While it can deflect comets emerging from the (far out) Oort Cloud, it can also redirect objects from the (nearer) asteroid belt towards our orbital plane, increasing the probability of a collision. See the following article for more information of the relationship between Jupiter and the Earth: Does Jupiter protect Earth from asteroids and comets?
Much of the information about Jupiter, accumulated over the last 50 years, has been derived from orbits along the (east-west) equatorial plane. See https://en.wikipedia.org/wiki/Jupiter. With the launch of the JUNO spacecraft on August 5, 2011, NASA directed JUNO’s orbit along the polar plane (north-south).
The following article provides some specifications of the spacecraft itself: Juno Spacecraft Description By Bill Kurth 2012-‐06-‐01.
It took about five years for the orbiter to reach Jupiter (July 2016), which included a gravitational assist from the Earth. View the animation at this link: Juno spacecraft trajectory animation.
Once there, JUNO took 36 polar orbits around the planet as shown in the video linked below.
Each orbit lasted 53 days with its perijove (closest) at about 2,100 kilometers and apojove (furthest) at the outer reaches of the Jovian magnetosphere.
JUNO revealed a trove of new information about Jupiter. Two recent findings stand out…
First: The epic storms at the poles. On August 27, 2016, on its closest pass to the planet, Juno obtained the first ever recording of the enormous cyclonic storms at each pole.
(Above: South pole. Below: North pole (false colors))
There are eight cyclones surrounding a central one at the north pole and five at the south pole (ranging from 2000-5000 kilometers in diameter)
Studies of these storms have yielded substantial data about Jupiter’s thermal dynamics. Detailed Infrared spectroscopy revealed that convection currents from the hot interior feed energy to the outer layer inducing tremendous cyclonic storms. See the following article for more information: Moist convection drives an upscale energy transfer at Jovian high latitudes. Interestingly, they exhibit features common to our own; providing a way to study a dynamic model of our own storm systems, but at a safe distance.
The second significant finding was that Jupiter is fuzzier than we thought.
Earlier theories about Jupiter’s formation were based on an accretion model. Some 4 billion years ago the planet’s solid core was first formed from heavier elements including ice, rock and metal: debris left over from the creation of the embryonic Solar System. It was presumed that over time, gravity would attract the swirling hydrogen and helium gases surrounding the core. That would ultimately lead to the formation of this gas giant. See NASA SVS | Creating Gas Giants.
Juno’s mission revealed that this model needed improvement. By measuring the subtle differences in Jupiter’s gravitational and magnetic fields, Juno found that the core extends farther than previously thought. Also, there does not appear to be a demarcation line between the core and the outer layers. See
Jupiter Revealed by Knowable Magazine. This newer finding is consistent with recent studies of exoplanet gas giants which showed that they formed earlier and faster than the current model would have predicted. The following article contains for information on exoplanet formation: Early Accretion of Large Amounts of Solids for Directly Imaged Exoplanets – IOPscience
While this issue may not affect the price of eggs, it is significant for our understanding of how our own Solar System formed. It is widely recognized that Jupiter’s evolution directly affected the position, size, mass and motion of the other planets. Finding out how this works will be the grist for more research.
For those interested in the most up to date NASA reports on the JUNO mission see: Science Findings – Mission Juno .
The impact of these two findings, (a small sample of all the data retrieved so far) and the satellite’s continued robustness, prompted NASA in 2021 to extend Juno’s five year mission for another five years (to 2026). In part, this was also because Juno provided new significant data about Jupiter’s four Galilean moons: a topic that will be covered in the next issue.
