Juno Data Shows that Some of Jupiter’s Moons are Leaving “Footprints” in its Aurorae

Since it arrived in orbit around Jupiter in July of 2016, the Juno mission has been sending back vital information about the gas giant’s atmosphere, magnetic field and weather patterns. With every passing orbit – known as perijoves, which take place every 53 days – the probe has revealed things about Jupiter that scientists will rely on to learn more about its formation and evolution.

Interestingly, some of the most recent information to come from the mission involves how two of its moons affect one of Jupiter’s most interesting atmospheric phenomenon. As they revealed in a recent study, an international team of researchers discovered how Io and Ganymede leave “footprints” in the planet’s aurorae. These findings could help astronomers to better understand both the planet and its moons.

The study, titled “Juno observations of spot structures and a split tail in Io-induced aurorae on Jupiter“, recently appeared in the journal Science. The study was led by A. Mura of the International Institute of Astrophysics (INAF) and included members from NASA’s Goddard Space Flight Center, NASA’s Jet Propulsion Laboratory, the Italian Space Agency (ASI), the Southwest Research Institute (SwRI), the Johns Hopkins University Applied Physics Laboratory (JHUAPL), and multiple universities.

Infrared images obtained by the Cassini probe, showing disturbances in Jupiter’s aurorae caused by Io and Ganymede. Credit: (c) Science (2018).

Much like aurorae here on Earth, Jupiter’s aurorae are produced in its upper atmosphere when high-energy electrons interact with the planet’s powerful magnetic field. However, as the Juno probe recently demonstrated using data gathered by Ultraviolet Spectrograph (UVS) and Jovian Energetic Particle Detector Instrument (JEDI), Jupiter’s magnetic field is significantly more powerful than anything we see on Earth.

In addition to reaching power levels 10 to 30 times greater than anything higher than what is experienced here on Earth (up to 400,000 electron volts), Jupiter’s norther and southern auroral storms also have oval-shaped disturbances that appear whenever Io and Ganymede pass close to the planet. As they explain in their study:

“A northern and a southern main auroral oval are visible, surrounded by small emission features associated with the Galilean moons. We present infrared observations, obtained with the Juno spacecraft, showing that in the case of Io, this emission exhibits a swirling pattern that is similar in appearance to a von Kármán vortex street.”

A Von Kármán vortex street, a concept in fluid dynamics, is basically a repeating pattern of swirling vortices caused by a disturbance. In this case, the team found evidence of a vortex streaming for hundreds of kilometers when Io passed close to the planet, but which then disappeared as the moon moved farther away from the planet.

Reconstructed view of Jupiter’s northern lights through the filters of the Juno Ultraviolet Imaging Spectrograph instrument on Dec. 11, 2016, as the Juno spacecraft approached Jupiter, passed over its poles, and plunged towards the equator. Credit: NASA/JPL-Caltech/Bertrand Bonfond

The team also found two spots in the auroral belt created by Ganymede, where the extended tail from the main auroral spots eventually split in two. While the team was not sure what causes this split, they venture that it could be caused by interaction between Ganymede and Jupiter’s magnetic field (since Ganymede is the only Jovian moon to have its own magnetic field).

These features, they claim, suggest that magnetic interactions between Jupiter and Ganymede are more complex than previously thought. They also indicate that neither of the footprints were where they expected to find them, which suggests that models of the planet’s magnetic interactions with its moons may be in need of revision.

Studying Jupiter’s magnetic storms is one of the primary goals of the Juno mission, as is learning more about the planet’s interior structure and how it has evolved over time. In so doing, astronomers hope to learn more about how the Solar System came to be. NASA also recently extended the mission to 2021, giving it three more years to gather data on these mysteries.

And be sure to enjoy this video of the Juno mission, courtesy of the Jet Propulsion Laboratory:

Further Reading: phys.org, Science

Jupiter’s Atmospheric Bands Go Surprisingly Deep

For centuries, astronomers have been observing Jupiter swirling surface and been awed and mystified by its appearance. The mystery only deepened when, in 1995, the Galileo spacecraft reached Jupiter and began studying its atmosphere in depth. Since that time, astronomers have puzzled over its colored bands and wondered if they are just surface phenomenon, or something that goes deeper.

Thanks to the Juno spacecraft, which has been orbiting Jupiter since July of 2016, scientists are now much closer to answering that question. This past week, three new studies were published based on Juno data that presented new findings on Jupiter’s magnetic field, its interior rotation, and how deep its belts extend. All of these findings are revising what scientists think of Jupiter’s atmosphere and its inner layers.

The studies were titled “Measurement of Jupiter’s asymmetric gravity field“, “Jupiter’s atmospheric jet streams extend thousands of kilometres deep” and “A suppression of differential rotation in Jupiter’s deep interior“, all of which were published in Nature on March 7th, 2018. The studies were led by Prof. Luciano Iess of Sapienza University of Rome, the second by Prof. Yohai Kaspi and Dr. Eli Galanti of the Weizmann Institute of Science, and the third by Prof. Tristan Guillot of the Observatoire de la Cote d’Azur.

Jupiter’s South Pole, taken during a Juno flyby on Dec 16th, 2017. Credit: NASA/JPL-Caltech/SwRI/MSSS/David Marriott

The research effort was led by Professo Kaspi and Dr. Galanti, who in addition to being the lead authors on the second study were co-authors on the other two. The pair have been preparing for this analysis even before Juno launched in 2011, during which time they built mathematical tools to analyze the gravitational field data and get a better grasp of Jupiter’s atmosphere and its dynamics.

All three studies were based on data gathered by Juno as it passed from one of Jupiter’s pole to the other every 53-days – a maneuver known as a “perijove”. With each pass, the probe used its advanced suite of instruments to peer beneath the surface layers of the atmosphere. In addition, radio waves emitted by the probe were measured to determine how they were shifted by the planet’s gravitational field with each orbit.

As astronomers have understood for some time, Jupiter’s jets flow in bands from east to west and west to east. In the process, they disrupt the even distribution of mass on the planet. By measuring changes in the planet’s gravity field (and thus this mass imbalance), Dr. Kaspi and Dr. Galanti’s analytical tools were able to calculate how deep the storms extend beneath the surface and what it’s interior dynamics are like.

Above all, the team expected to find anomalies because of the way the planet deviates from being a perfect sphere – which is due to how its rapid rotation squishes it slightly. However, they also looked for additional anomalies that could be explained due to the presence of powerful winds in the atmosphere.

This image from Juno’s JunoCam captured the south pole in visible light only. It’s a puzzle why the north and south poles are so similar, yet have a different number of cyclones. Image: NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles

In the first study, Dr. Iess and his colleagues used precise Doppler tracking of the Juno spacecraft to conduct measurements of Jupiter’s gravity harmonics – both even and odd. What they determined was Jupiter’s magnetic field has a north-south asymmetry, which is indicative of interior flows in the atmosphere.

Analysis of this asymmetry was followed-up on in the second study, where Dr. Kaspi, Dr. Galanti and their colleagues used the variations in the planet’s gravity field to calculate the depth of Jupiter’s east-west jet streams. By measuring how these jets cause an imbalance in Jupiter’s gravity field, and even disrupt the mass of the planet, they concluded that they extend to a depth of 3000 km (1864 mi).

From all this, Prof. Guillot and his colleagues conducted the third study, where they used the previous findings about the planet’s gravitational field and jet streams and compared the results to predictions of interior models. From this, they determined that the interior of the planet rotates almost like a rigid body and that differential rotation decreases farther down.

In addition, they found that the zones of atmospheric flow extended to between 2,000 km (1243 mi) and 3,500 km (2175 mi) deep, which was consistent with the constraints obtained from the odd gravitational harmonics. This depth also corresponds to the point where electric conductivity would become large enough that magnetic drag would suppress differential rotation.

Based on their findings, the team also calculated that Jupiter’s atmosphere constitutes 1% of its total mass. For comparison, Earth’s atmosphere is less than a millionth of its total mass. Still, as Dr. Kaspi explained in Weizzmann Institute press release, this was rather surprising:

“That is much more than anyone thought and more than what has been known from other planets in the Solar System. That is basically a mass equal to three Earths moving at speeds of tens of meters per second.”

All told, these studies have shed new light on the Jupiter’s atmospheric dynamics and interior structure. At present, the subject of what resides at Jupiter’s core remains unresolved. But the researchers hope to analyze further measurements made by Juno to see whether Jupiter has a solid core and (if so) to determine its mass. This in turn will help astronomers learn a great deal about the Solar System’s history and formation.

In addition, Kaspi and Galanti are looking to use some of the same methods they developed to characterize Jupiter’s jet streams to tackle its most iconic feature – Jupiter’s Great Red Spot. In addition to determining how deep this storm extends, they also hope to learn why this storm has persisted for so many centuries, and why it has been noticeably shrinking in recent years.

The Juno mission is expected to wrap up in July of 2018. Barring any extensions, the probe will conduct a controlled deorbit into Jupiter’s atmosphere after conducting perijove 14. However, even after the mission is over, scientists will be analyzing the data it has collected for years to come. What this reveals about the Solar System’s largest planet will also go a long way towards informing out understanding of the Solar System.

Further Reading: Weizmann Institute of Science, Nature, Nature (2), Nature (3),

Juno Finds that Jupiter’s Gravitational Field is “Askew”

Since it established orbit around Jupiter in July of 2016, the Juno mission has been sending back vital information about the gas giant’s atmosphere, magnetic field and weather patterns. With every passing orbit – known as perijoves, which take place every 53 days – the probe has revealed more interesting things about Jupiter, which scientists will rely on to learn more about its formation and evolution.

During its latest pass, the probe managed to provide the most detailed look to date of the planet’s interior. In so doing, it learned that Jupiter’s powerful magnetic field is askew, with different patterns in it’s northern and southern hemispheres. These findings were shared on Wednesday. Oct. 18th, at the 48th Meeting of the American Astronomical Society’s Division of Planetary Sciencejs in Provo, Utah.

Ever since astronomers began observing Jupiter with powerful telescopes, they have been aware of its swirling, banded appearance. These colorful stripes of orange, brown and white are the result of Jupiter’s atmospheric composition, which is largely made up of hydrogen and helium but also contains ammonia crystals and compounds that change color when exposed to sunlight (aka. chromofores).

Illustration of NASA’s Juno spacecraft firing its main engine to slow down and go into orbit around Jupiter. Credit: NASA/Lockheed Martin

Until now, researchers have been unclear as to whether or not these bands are confined to a shallow layer of the atmosphere or reach deep into the interior of the planet. Answering this question is one of the main goals of the Juno mission, which has been studying Jupiter’s magnetic field to see how it’s interior atmosphere works. Based on the latest results, the Juno team has concluded that hydrogen-rich gas is flowing asymmetrically deep in the planet.

These findings were also presented in a study titled Comparing Jupiter interior structure models to Juno gravity measurements and the role of a dilute core, which appeared in the May 28th issue of Geophysical Research Letters. The study was led by Sean Wahl, a grad student from UC Berkeley, and included members from the Weizmann Institute of Science, the Southwest Research Institute (SwRI), NASA’s Goddard Space Flight Center and the Jet Propulsion Laboratory.

Another interesting find was that Jupiter’s gravity field varies with depth, which indicated that material is flowing as far down as 3,000 km (1,864 mi). Combined with information obtained during previous perijoves, this latest data suggests that Jupiter’s core is small and poorly defined. This flies in the face of previous models of Jupiter, which held that the outer layers are gaseous while the interior ones are made up of metallic hydrogen and a rocky core.

As Tristan Guillot – a planetary scientist at the Observatory of the Côte d’Azur in Nice, France, and a co-author on the study – indicated during the meeting, “This is something that was not expected. We were not sure at all whether we would be able to see that… It’s clear that giant planets have a lot of secrets.”

 

This artist's illustration shows Juno's Microwave Radiometer observing deep into Jupiter's atmosphere. The image shows real data from the 6 MWR channels, arranged by wavelength. Credit: NASA/SwRI/JPL
This artist’s illustration shows Juno’s Microwave Radiometer observing deep into Jupiter’s atmosphere. The image shows real data from the 6 MWR channels, arranged by wavelength. Credit: NASA/SwRI/JPL

But of course, more passes and data are needed in order to pinpoint how strong the flow of gases are at various depths, which could resolve the question of how Jupiter’s interior is structured. In the meantime, the Juno scientists are pouring over the probe’s gravity data hoping to see what else it can teach them. For instance, they also want to know how far the Great Red Spot extends into the amotpshere.

This anticyclonic storm, which was first spotted in the 17th century, is Jupiter’s most famous feature. In addition to being large enough to swallow Earth whole – measuring some 16,000 kilometers (10,000 miles) in diameter – wind speeds can reach up to 120 meters per second (432 km/h; 286 mph) at its edges. Already the JunoCam has snapped some very impressive pictures of this storm, and other data has indicated that the storm could run deep.

In fact, on July 10th, 2017, the Juno probe passed withing 9,000 km (5,600 mi) of the Great Red Spot, which took place during its sixth orbit (perijove six) of Jupiter. With it’s suite of eight scientific instruments directed at the storm, the probe obtained readings that indicated that the Great Red Spot could also extend hundreds of kilometers into the interior, or possibly even deeper.

As David Stevenson, a planetary scientist at the California Institute of Technology and a co-author on the study, said during the meeting, “It’s not yet clear that it is so deep it will show up in gravity data. But we’re trying”.

Jupiter’s Great Red Spot, as imaged by the Juno spacecraft’s JunoCam at a distance of just 9,000 km (5,600 mi) from the atmosphere. Credit : NASA/SwRI/MSSS/TSmith

Other big surprises which Juno has revealed since it entered orbit around Jupiter include the clusters of cyclones located at each pole. These were visible to the probe’s instruments in both the visible and infrared wavelengths as it made its first maneuver around the planet, passing from pole to pole. Since Juno is the first space probe in history to orbit the planet this way, these storms were previously unknown to scientists.

In total, Juno spotted eight cyclonic storms around the north pole and five around the south pole. Scientists were especially surprised to see these, since computer modelling suggests that such small storms would not be stable around the poles due to the planet’s swirling polar winds. The answer to this, as indicated during the presentation, may have to do with a concept known as vortex crystals.

As Fachreddin Tabataba-Vakili – a planetary scientist at NASA’s Jet Propulsion Laboratory and a co-author on the study – explained, such crystals are created when small vortices form and persist as the material in which they are embedded continues to flow. This phenomenon has been seen on Earth in the form of rotating superfluids, and Jupiter’s swirling poles may possess similar dynamics.

In the short time that Juno has been operating around Jupiter, it has revealed much about the planet’s atmosphere, interior, magnetic field and internal dynamics. Long after the mission is complete – which will take place in February of 2018 when the probe is crashed into Jupiter’s atmosphere – scientists are likely to be sifting through all the data it obtained, hoping to solve any remaining mysteries from the Solar System’s largest and most massive planet.

Further Reading: Nature

How Do We Terraform Jupiter’s Moons?

Continuing with our “Definitive Guide to Terraforming“, Universe Today is happy to present to our guide to terraforming Jupiter’s Moons. Much like terraforming the inner Solar System, it might be feasible someday. But should we?

Fans of Arthur C. Clarke may recall how in his novel, 2010: Odyssey Two (or the movie adaptation called 2010: The Year We Make Contact), an alien species turned Jupiter into a new star. In so doing, Jupiter’s moon Europa was permanently terraformed, as its icy surface melted, an atmosphere formed, and all the life living in the moon’s oceans began to emerge and thrive on the surface.

As we explained in a previous video (“Could Jupiter Become a Star“) turning Jupiter into a star is not exactly doable (not yet, anyway). However, there are several proposals on how we could go about transforming some of Jupiter’s moons in order to make them habitable by human beings. In short, it is possible that humans could terraform one of more of the Jovians to make it suitable for full-scale human settlement someday.

Continue reading “How Do We Terraform Jupiter’s Moons?”