The Juno Infrared Auroral Mapper (JIRAM) captured this infrared image of Jupiter's south pole. This part of Jupiter cannot be seen from Earth. Image: NASA/JPL-Caltech/SwRI/MSSS
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.
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:
Artist’s illustration of Jupiter and Europa (in the foreground) with the Galileo spacecraft after its pass through a plume erupting from Europa’s surface. Credits: NASA/JPL-Caltech/Univ. of Michigan
Jupiter’s moon Europa continues to fascinate and amaze! In 1979, the Voyager missions provided the first indications that an interior ocean might exist beneath it’s icy surface. Between 1995 and 2003, the Galileo spaceprobe provided the most detailed information to date on Jupiter’s moons to date. This information bolstered theories about how life could exist in a warm water ocean located at the core-mantle boundary.
Even though the Galileo mission ended when the probe crashed into Jupiter’s atmosphere, the spaceprobe is still providing vital information on Europa. After analyzing old data from the mission, NASA scientists have found independent evidence that Europa’s interior ocean is venting plumes of water vapor from its surface. This is good news for future mission to Europa, which will attempt to search these plumes for signs of life.
The study which describes their findings, titled “Evidence of a plume on Europa from Galileo magnetic and plasma wave signatures“, recently appeared in the journal Nature Astronomy. The study was led by Xianzhe Jia, a space physicist from the Department of Climate and Space Sciences and Engineering at the University of Michigan, and included members from UCLA and the University of Iowa.
Artist’s concept of the Galileo space probe passing through the Jupiter system. Credit: NASA
The data was collected in 1997 by Galileo during a flyby of Europa that brought it to within 200 km (124 mi) of the moon’s surface. At the time, its Magnetometer (MAG) sensor detected a brief, localized bend in Jupiter’s magnetic field, which remained unexplained until now. After running the data through new and advanced computer models, the team was able to create a simulation that showed that this was caused by interaction between the magnetic field and one of the Europa’s plumes.
This analysis confirmed ultraviolet observations made by NASA’s Hubble Space Telescope in 2012, which suggested the presence of water plumes on the moon’s surface. However, this new analysis used data collected much closer to the source, which indicated how Europa’s plumes interact with the ambient flow of plasma contained within Jupiter’s powerful magnetic field.
In addition to being the lead author on this study, Jia is also the co-investigator for two instruments that will travel aboard the Europa Clipper mission – which may launch as soon as 2022 to explore the moon’s potential habitability. Jia’s and his colleagues were inspired to reexamine data from the Galileo mission thanks to Melissa McGrath, a member of the SETI Institute and also a member of the Europa Clipper science team.
During a presentation to her fellow team scientists, McGrath highlighted other Hubble observations of Europa. As Jiang explained in a recent NASA press release:
“The data were there, but we needed sophisticated modeling to make sense of the observation. One of the locations she mentioned rang a bell. Galileo actually did a flyby of that location, and it was the closest one we ever had. We realized we had to go back. We needed to see whether there was anything in the data that could tell us whether or not there was a plume.”
Artist’s impression of a water vapor plume on Europa. Credit: NASA/ESA/K. Retherford/SWRI
When they first examined the information 21 years ago, the high-resolution data obtained by the MAG instrument showed something strange. But it was thanks to the lessons provided by the Cassini mission, which explored the plumes on Saturn’s moon Enceladus, that the team knew what to look for. This included material from the plumes which became ionized by the gas giant’s magnetosphere, leaving a characteristic blip in the magnetic field.
After reexamining the data, they found that the same characteristic bend (localized and brief) in the magnetic field was present around Europa. Jia’s team also consulted data from Galileo’sPlasma Wave Spectrometer (PWS) instrument to measure plasma waves caused by charged particles in gases around Europa’s atmosphere, which also appeared to back the theory of a plume.
This magnetometry data and plasma wave signatures were then layered into new 3D modeling developed by the team at the University of Michigan (which simulated the interactions of plasma with Solar system bodies). Last, they added the data obtained from Hubble in 2012 that suggested the dimensions of the potential plumes. The end result was a simulated plume that matched the magnetic field and plasma signatures they saw in the Galileo data.
As Robert Pappalardo, a Europa Clipper project scientist at NASA’s Jet Propulsion Laboratory (JPL), indicated:
“There now seem to be too many lines of evidence to dismiss plumes at Europa. This result makes the plumes seem to be much more real and, for me, is a tipping point. These are no longer uncertain blips on a faraway image.”
Artist’s concept of a Europa Clipper mission, which will study Europa in 2022-2025 to search for signs of life. Credit: NASA/JPL
The findings are certainly good news for the Europa Clipper mission, which is expected to make the journey to Jupiter between 2022 and 2025. When this probe arrives in the Jovian system, it will establish an orbit around Jupiter and conduct rapid, low-altitude flybys of Europa. Assuming that plume activity does take place on the surface of the moon, the Europa Clipper will sample the frozen liquid and dust particles for signs of life.
“If plumes exist, and we can directly sample what’s coming from the interior of Europa, then we can more easily get at whether Europa has the ingredients for life,” Pappalardo said. “That’s what the mission is after. That’s the big picture.”
At present, the mission team is busy looking at potential orbital paths for the Europa Clipper mission. With this new research in hand, the team will choose a path that will take the spaceprobe above the plume locations so that it is in an ideal position to search them for signs of life. If all goes as planned, the Europa Clipper could be the first of several probes that finally proves that there is life beyond Earth.
And be sure to check out this video of the Europa Clipper mission, courtesy of NASA:
JunoCam took this image during its eleventh close flyby of Jupiter on February 7, 2018. Image credit: NASA / JPL / SwRI / MSSS / David Marriott.
It is a well-known fact among Earth scientists that our planet periodically undergoes major changes in its climate. Over the course of the past 200 million years, our planet has experienced four major geological periods (the Triassic, Jurassic and Cretaceous and Cenozoic) and one major ice age (the Pliocene-Quaternary glaciation), all of which had a drastic impact on plant and animal life, as well as effecting the course of species evolution.
For decades, geologists have also understood that these changes are due in part to gradual shifts in the Earth’s orbit, which are caused by Venus and Jupiter, and repeat regularly every 405,000 years. But it was not until recently that a team of geologists and Earth scientists unearthed the first evidence of these changes – sediments and rock core samples that provide a geological record of how and when these changes took place.
Professor Dennis Kent with part of a 1,700-foot-long rock core obtained from Petrified Forest National Park in Arizona. Credit: Nick Romanenko/Rutgers University
As noted, the idea that Earth experiences periodic changes in its climate (which are related to changes in its orbit) has been understood for almost a century. These changes consist of Milankovitch Cycles, which consist of a 100,000-year cycle in the eccentricity of Earth’s orbit, a 41,000-year cycle in the tilt of Earth’s axis relative to its orbital plane, and a 21,000-year cycle caused by changes in the planet’s axis.
Combined with the 405,000-year swing, which is the result of Venus and Jupiter’s gravitational influence, these shifts cause changes in how much solar energy reaches parts of our planet, which in turn influences Earth’s climate. Based on fossil records, these cycles are also known to have had a profound impact on life on Earth, which likely had an effect on the course of species of evolution. As Prof. Bent explained in a Rutgers Today press release:
“The climate cycles are directly related to how Earth orbits the sun and slight variations in sunlight reaching Earth lead to climate and ecological changes. The Earth’s orbit changes from close to perfectly circular to about 5 percent elongated especially every 405,000 years.”
For the sake of their study, Prof. Kent and his colleagues obtained sediment samples from the Newark basin, a prehistoric lake that spanned most of New Jersey, and a core rock sample from the Chinle Formation in Petrified Forest National Park in Arizona. This core rock measured about 518 meters (1700 feet) long, 6.35 cm (2.5 inches) in diameter, and was dated to the Triassic Period – ca. 202 to 253 million years ago.
Within ancient rocks in Arizona’s Petrified Forest National Park, scientists have identified signs of a regular variation in Earth’s orbit that influences climate. Credit: Kevin Krajick/Lamont-Doherty Earth Observatory
The team then linked reversals in Earth’s magnetic field – where the north and south pole shift – to sediments with and without zircons (minerals with uranium that allow for radioactive dating) as well as to climate cycles in the geological record. What these showed was that the 405,000-years cycle is the most regular astronomical pattern linked to Earth’s annual orbit around the Sun.
The results further indicated that the cycle been stable for hundreds of millions of years and is still active today. As Prof. Kent explained, this constitutes the first verifiable evidence that celestial mechanics have played a historic role in natural shifts in Earth’s climate. As Prof. Kent indicated:
“It’s an astonishing result because this long cycle, which had been predicted from planetary motions through about 50 million years ago, has been confirmed through at least 215 million years ago. Scientists can now link changes in the climate, environment, dinosaurs, mammals and fossils around the world to this 405,000-year cycle in a very precise way.”
Previously, astronomers were able to calculate this cycle reliably back to around 50 million years, but found that the problem became too complex prior to this because too many shifting motions came into play. “There are other, shorter, orbital cycles, but when you look into the past, it’s very difficult to know which one you’re dealing with at any one time, because they change over time,” said Prof. Kent. “The beauty of this one is that it stands alone. It doesn’t change. All the other ones move over it.”
The super-continent Pangaea during the Permian period (300 – 250 million years ago). Credit: NAU Geology/Ron Blakey
In addition, scientists were unable to obtain accurate dates as to when Earth’s magnetic field reversed for 30 million years of the Late Triassic – between ca. 201.3 and 237 million years ago. This was a crucial period for the evolution of terrestrial life because it was when the Supercontinent of Pangaea broke up, and also when the dinosaurs and mammals first appeared.
This break-up led to the formation of the Atlantic Ocean as the continents drifted apart and coincided with a mass extinction event by the end of the period that effected the dinosaurs. With this new evidence, geologists, paleontologists and Earth scientists will be able to develop very precise timelines and accurately categorize fossil evidence dated to this period, which show differences and similarities over wide-ranging areas.
This research, and the ability to create accurate geological and climatological timelines that go back over 200 million years, is sure to have drastic implications. Not only will climate studies benefit from it, but also our understanding of how life, and even how our Solar System, evolved. What emerges from this could include a better understanding of how life could emerge in other star systems.
After all, if our search for extra-solar life life comes down to what we know about life on Earth, knowing more about how it evolved here will better the odds of finding it out there.
A recent capture of Jupiter from April 21st. Image credit and copyright: Efrain Morales.
A recent capture of Jupiter from April 21st. Image credit and copyright: Efrain Morales Rivera.
It’s a question I’ve fielded lots this weekend leading up to last night’s April Pink Full Moon, and one I expect we’ll get again tonight: “What’s that bright star near the Moon?”
That bright “star” is actually a planet, the king of them all as far as our Solar System is concerned: Jupiter. May also ushers in Jupiter observing season, as the planet reaches opposition on May 9th, rising in the east opposite to the setting Sun to the west. Jupiter now joins Venus in the dusk sky, ending the planetary drought plaguing many an evening star party.
Looking east tonight (April 30th) at 9 PM local. Created using Stellarium.
All planetary news seems to lead back to Jupiter this season. Just last week, we wrote about a recent study, suggesting that Jupiter actually gets hit by asteroids and comets on a much more regular basis than astronomers thought.
It’s always worth keeping a sharp eye on Jupiter. Shining a magnitude -2.5 near opposition, you can even pick Jupiter out against the deep blue daytime sky… if you know exactly where to look for it. The Moon visits Jupiter once every orbit, and the next time to try this feat of visual athletics is on May 27th, just before sunset.
Jupiter is 4.4 astronomical units (658 million kilometers) distant at opposition this year, and presents a disk 45” across.
At the eyepiece, Jupiter presents a roiling upper atmosphere, completing an amazing rotation once every 9.9 hours. This is not only fast enough to give Jove a noticeable equatorial bulge at its equator, but you can also observe and image Jupiter in its entirety in just one clear evening.
One of the first things that becomes apparent observing Jupiter at low power are its retinue of four Galilean moons. These are, from interior outward: Io, Europa, Ganymede and Callisto. Speedy Io takes just 1.8 days to orbit Jupiter once, while outermost Callisto takes a leisurely 16.7 days to make one circuit around Jupiter. Not only is it fun to note the changes in configuration of Jupiter’s major moons from night to night, but it’s interesting to watch them cast shadows onto Jupiter’s cloud tops and alternately disappear and reappear in and out of Jupiter’s shadow.
Two shadows crossing the face of Jupiter on July 30th, 2018. Created using Stellarium.
A few times a year, you can catch two moons casting a shadow on Jupiter at once. These usually happen in seasons, with the next pair involving Io and Europa (the most frequent transiters) set to occur on July 30th, 2018. Rarer still are triple transits, which last occurred on January 24th, 2015 and will happen next on March 20th, 2032. You’ll never see a quadruple transit though… and the outermost moon Callisto is the only one that can “miss” Jupiter, as it does in 2018.
The celestial scene changes, too, like a spotlight cast over the stage of the sky. At opposition, for example, Jupiter and its moons cast their respective shadows straight back, nearly behind them from our perspective. Watch how this changes, however, as Jupiter heads towards quadrature at 90 degrees elongation east of the Sun on August 6th, 2018 and we see Jupiter and its moons cast their shadows to the side.
Danish astronomer Ole Rømer noted a discrepancy in the timings of shadow transits near opposition versus quadrature and correctly realized that light from the events was actually taking time to transit from Jupiter to his telescope on Earth, and made the first crude measurement of the speed of light in 1676.
Crank up the magnification, and the Great Red Spot will pop into view if it’s turned Earthward. Though this centuries-long storm has been shrinking in recent years, it also seems to be condensing and reddening once again, versus the pale salmon color its exhibited as of late. How old is the Great Red Spot? Will it disappear this century, disappointing legions of school kids who diligently crayon in a ruby red eye on Jove?
One thing is for sure; the face of Jove does change over time. Another interesting example is the disappearing act that Jove’s Southern Equatorial Belt (SEB) makes every decade or so… this last occurred during 2010 season, and we may soon be due again. It would be an amazing scientific opportunity if this were to occur before NASA’s Juno spacecraft completes its mission this summer. Our question: why does the SEB disappear, while the NEB seems to be a permanent fixture on Jove?
All mysteries presented by the largest planet in our solar system, this opposition season 2018.
Pow: The July 1994 impact of Comet Shoemaker-Levy 9 on Jupiter, captured by the Hubble Space Telescope. Credit: R. Evans/J. Trauger/H. Hammel/HST Comet Science Team/NASA.
Pow: The July 1994 impact of Comet Shoemaker-Levy 9 on Jupiter, captured by the Hubble Space Telescope. Credit: R. Evans/J. Trauger/H. Hammel/HST Comet Science Team/NASA.
Are you keeping a eye on Jupiter? The King of the Planets, Jove presents a swirling upper atmosphere full of action, a worthy object of telescopic study as it heads towards another fine opposition on May 9th, 2018.
Now, an interesting international study out of the School of Engineering in Bilbao, Spain, the Astronomical Society of France, the Meath Astronomical Group in Dublin Ireland, the Astronomical Society of Australia, and the Esteve Duran Observatory in Spain gives us a fascinating and encouraging possibly, and another reason to keep a sharp eye on old Jove: Jupiter may just get smacked with asteroids on a more regular basis than previously thought.
The study is especially interesting, as it primarily focused in on flashes chronicled by amateur imagers and observers in recent years. In particular, researchers focused on impact events witnessed on March 17th 2016 and May 26th, 2017, along with the comparison of exogenous (of cosmic origin) dust measured in the upper atmosphere. This allowed researchers to come up with an interesting estimate: Jupiter most likely gets hit by an asteroid 5-20 meters in diameter (for comparison, the Chelyabinsk bolide was an estimated 20 meters across) 10 to 65 times every year, though researchers extrapolate that a dedicated search might only nab an impact flash or scar once every 0.4 to 2.4 years or so.
Compare this impact rate with the Earth, which gets hit by a Chelyabinsk-sized 20-meter impactor about once every half century or so. Incidentally, we know this impact rate on Earth better than ever before, largely due to U.S. Department of Defense classified assets in space continually watching for nuclear tests and missile launches, which also pick up an occasional meteor “photobomb.”
Small asteroid impacts over the span of the Earth over a 20 year period. NASA/Planetary Science.
One reason we may never have witnessed a meteor impact on Jupiter is, astronomers (both professional and amateur) never thought to look for them. The big wake-up call was the impact of Comet Shoemaker-Levy 9 in July 1994, an event witnessed by the newly refurbished Hubble Space Telescope as the resulting impact scars were easily visible in backyard telescopes for weeks afterward. Back in the day, speculation was rampant in the days leading up to the impact: would the collision be visible at all? Or would gigantic Jupiter simply gobble up the tiny comet fragments with nary a belch?
Australian amateur astronomer Anthony Wesley also caught an interesting impact (scar?) in 2009, and every few years or so, we get word of an elusive flash reported on the Jovian cloudtops, sometimes corroborated by a secondary independent observation or a resulting impact scar, and sometimes not.
An impact scar (top center on the disk) on Jupiter, captured on July 19th, 2009. Image credit: Anthony Wesley.
Of course, there are factors which will lower said ideal versus the actual observed impact rate. There’s always a month or so a year, for example, when Jupiter is near solar conjunction on the far side of the Sun, and out of range for observation. Also, we only see half of the Jovian disk from our Earthly perspective at any given time, and we’re about to lose our only set of eyes in orbit around Jupiter – NASA’s Juno spacecraft – later this summer, unless there’s a last minute mission extension.
On the plus side, however, Jupiter is a fast rotator, spinning on its axis once every 9.9 hours. This also means that near opposition, you can also track Jupiter through one full rotation in a single evening.
Finding Jupiter: looking eastward tonight at around 11PM local. Credit Stellarium.
Then there’s the planet’s location in the sky: Currently, Jupiter’s crossing the southern constellation of Libra, and opposition for Jove moves about one astronomical constellation eastward along the ecliptic a year. Jupiter will bottom out along the ecliptic in late 2019, and won’t pop back up north of the celestial equator until May 2022. And while it’s not impossible for northern observers to keep tabs on Jupiter when it’s down south, we certainly get more gaps in coverage around this time.
Hale-Bopp’s close inbound passage near Jupiter in 1996. Credit: NASA/JPL-Horizons.
Should we hail Jove as a protective ‘cosmic goal-tender,’ or fear it as the bringer of death and destruction? There are theories that Jupiter may be both: for example, Jupiter altered the inbound path of Comet Hale-Bopp in 1997, shortening its orbital period from 4,200 to 2,533 years. The 2000 book Rare Earth even included the hypothesis of Jupiter as a cosmic debris sweeper as one of the factors for why life evolved on Earth… if this is true, it’s an imperfect one, as Earth does indeed still get hit as well.
All reasons to keep an eye on Jupiter in the 2018 opposition season.
NASA / JPL-Caltech / SwRI / ASI / INAF /JIRAM / Roman Tkachenko
An amazingly active Io, Jupiter’s “pizza moon” shows multiple volcanoes and hot spots in this photo taken with Juno’s infrared camera. Credit: NASA / JPL-Caltech / SwRI / ASI / INAF /JIRAM / Roman Tkachenko
Volcanic activity on Io was discovered by Voyager 1 imaging scientist Linda Morabito. She spotted a little bump on Io’s limb while analyzing a Voyager image and thought at first it was an undiscovered moon. Moments later she realized that wasn’t possible — it would have been seen by earthbound telescopes long ago. Morabito and the Voyager team soon came to realize they were seeing a volcanic plume rising 190 miles (300 km) off the surface of Io. It was the first time in history that an active volcano had been detected beyond the Earth. For a wonderful account of the discovery, click here.
Linda Morabito spotted the puzzling plume off Io’s limb in this photo, taken on March 8, 1979, three days after Voyager 1’s encounter with Jupiter. It really does look like another moon poking out from behind Io. A second plume over the terminator (border between day and night) catches the rays of the rising Sun. Credit: NASA / JPL
Today, we know that Io boasts more than 130 active volcanoes with an estimated 400 total, making it the most volcanically active place in the Solar System. Juno used its Jovian Infrared Aurora Mapper (JIRAM) to take spectacular photographs of Io during Perijove 7 last July, when we were all totally absorbed by close up images of Jupiter’s Great Red Spot.
Io is captured here by NASA’s Galileo spacecraft. Deposits of sulfur dioxide frost appear in white and grey hues while yellowish and brownish hues are probably due to other sulfurous materials. Bright red materials, such as the prominent ring surrounding Pele (lower left), and “black” spots mark areas of recent volcanic activity. Credit: NASA / JPL / University of Arizona
Juno’s Io looks like it’s on fire. Because JIRAM sees in infrared, a form of light we sense as heat, it picked up the signatures of at least 60 hot spots on the little moon on both the sunlight side (right) and the shadowed half. Like all missions to the planets, Juno’s cameras take pictures in black and white through a variety of color filters. The filtered views are later combined later by computers on the ground to create color pictures. Our featured image of Io was created by amateur astronomer and image processor Roman Tkachenko, who stacked raw images from this data set to create the vibrant view.
This map shows thermal emission from erupting volcanoes on Io. The larger the spot, the larger the thermal emission. Credit: NASA/JPL-Caltech/Bear Fight Institute
Io’s hotter than heck with erupting volcano temperatures as high as 2,400° F (1,300° C). Most of its lavas are made of basalt, a common type of volcanic rock found on Earth, but some flows consist of sulfur and sulfur dioxide, which paints the scabby landscape in unique colors.
This five-frame sequence taken by NASA’s New Horizons spacecraft on March 1, 2007 captures the giant plume from Io’s Tvashtar volcano.
Located more than 400 million miles from the Sun, how does a little orb only a hundred miles larger than our Moon get so hot? Europa and Ganymede are partly to blame. They tug on Io, causing it to revolve around Jupiter in an eccentric orbit that alternates between close and far. Jupiter’s powerful gravity tugs harder on the moon when its closest and less so when it’s farther away. The “tug and release”creates friction inside the satellite, heating and melting its interior. Io releases the pent up heat in the form of volcanoes, hot spots and massive lava flows.
This wondrous image of Jupiter's south pole shows the arrangement of cyclones that is unique in our Solar System: five circumpolar cyclones perfectly arranged around a single polar cyclone. Image: NASA/SWRI/JPL/ASI/INAF/IAPS
When the Juno spacecraft arrived at Jupiter in July 2016, it quickly got to work. Among the multitude of stunning images of the planet were our first ever images of Jupiter’s poles. And what we saw there was a huge surprise: geometric arrangements of cyclones in persistent patterns.
Jupiter’s polar regions have always been a mystery to Earth-bound observers. The planet isn’t tilted much, which means the poles are always tantalizingly out of view. Other spacecraft visiting Jupiter have focused on the equatorial regions, but Juno’s circumpolar orbit is giving us good, close-up views of Jupiter’s poles.
“They are extraordinarily stable arrangements of such chaotic elements. We’d never seen anything like it.” – Morgan O’Neill, University of Chicago
Juno has a whole suite of instruments designed to unlock some of the mysteries surrounding Jupiter, including an infrared imager and a visible light camera. The polar regions are a particular focus for the mission, and astronomers were looking forward to their first views of Jupiter’s hidden poles. They were not disappointed when they got them.
Each of Jupiter’s poles is a geometric array of large cyclones arranged in persistent, polygonal patterns. At the north pole, eight storms are arranged around a single polar cyclone. In the south, one storm is encircled by five others.
Jupiter’s north pole is an arrangement of 8 cyclones around one central cyclone. Image: NASA/SWRI/JPL/ASI/INAF/IAPS
This was a stunning discovery, and quickly led to questions around the why and the how of these storm arrangements. Jupiter’s atmosphere is dominated by storm activity, including the well-known horizontal storm bands in the equatorial regions, and the famous Great Red Spot. But these almost artful arrangements of polar storms were something else.
The persistent arrangement of the storms is a puzzle. Our current understanding tells us that the storms should drift around and merge, but these storms do neither. They just turn in place.
A new paper published in Nature is looking deeper into these peculiar arrangements of storms. The paper is by scientists from an international group of institutions including the University of Chicago. It’s one of four papers dedicated to new observations from the Juno spacecraft.
One of the paper’s co-authors is Morgan O’Neill, a University of Chicago postdoctoral scholar. Remarking on the storms, she had this to say: “They are extraordinarily stable arrangements of such chaotic elements. We’d never seen anything like it.”
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
The strange geometrical arrangement of Jupiter’s polar storms reminded O’Neill of something from the library of strange physical phenomena only observed under laboratory conditions. Back in the ’90s, scientists had used electrons to simulate a frictionless, turbulent 2-D fluid as it cools. In those conditions, they observed similar behaviour. Rather than merging like expected, small vortices clumped together and formed equally spaced arrays around a center. They called these arrays “vortex crystals.”
This could help explain what’s happening at Jupiter’s poles, but it’s too soon to be certain. “The next step is: Can you create a model that builds a virtual planet and predicts these flows?” O’Neill said. That’ll be the next step in understanding the phenomenon.
Maybe it’s not surprising that these delicate-looking storms at the poles are so persistent. After all, the Great Red Spot on Jupiter has been visible for over 200 years. Maybe Jupiter is just huge and stable.
But the polar cyclones still require an explanation. And whatever that explanation is, understanding what’s happening on Jupiter will help us understand other planets better.
This artist's conception illustrates the brown dwarf named 2MASSJ22282889-431026, observed by NASA's Hubble and Spitzer space telescopes. Brown dwarfs are more massive and hotter than planets but lack the mass required to become stars.
Image credit: NASA
When is a Brown Dwarf star not a star at all, but only a mere Gas Giant? And when is a Gas Giant not a planet, but a celestial object more akin to a Brown Dwarf? These questions have bugged astronomers for years, and they go to the heart of a new definition for the large celestial bodies that populate solar systems.
An astronomer at Johns Hopkins University thinks he has a better way of classifying these objects, and it’s not based only on mass, but on the company the objects keep, and how the objects formed. In a paper published in the Astrophysical Journal, Kevin Schlaufman made his case for a new system of classification that could helps us all get past some of the arguments about which object is a gas giant planet or a brown dwarf. Mass is the easy-to-understand part of this new definition, but it’s not the only factor. How the object formed is also key.
In general, the less massive a star, the cooler it is. Though stars smaller than our Sun can still sustain heat-producing fusion reactions, protostars that are too small cannot. These “failed” stars are commonly known as brown dwarfs, and a new definition puts their range from between 10-75 times the mass of Jupiter. This artist’s concept compares the size of a brown dwarf to that of Earth, Jupiter, a low-mass star, and the Sun. (Credit: NASA/JPL-Caltech/UCB).
Schlaufman is an assistant professor in the Johns Hopkins Department of Physics and Astronomy. He has set a limit for what we should call a planet, and that limit is between 4 and 10 times the mass of our Solar System’s biggest planet, Jupiter. Above that, you’ve got yourself a Brown Dwarf star. (Brown Dwarfs are also called sub-stellar objects, or failed stars, because they never grew massive enough to become stars.)
“An upper boundary on the masses of planets is one of the most prominent details that was missing.” – Kevin Schlaufman, Johns Hopkins University, Dept. of Physics and Astronomy.
Improvements in observing other solar systems have led to this new definition. Where previously we only had our own Solar System as reference, we now can observe other solar systems with increasing effectiveness. Schlaufman observed 146 solar systems, and that allowed him to fill in some of the blanks in our understanding of brown dwarf and planet formation.
An image of Jupiter showing its storm systems. According to a new definition, Jupiter would be considered a brown dwarf if it had grown to over 10 times its mass when it was formed. Image: Gemini
“While we think we know how planets form in a big picture sense, there’s still a lot of detail we need to fill in,” Schlaufman said. “An upper boundary on the masses of planets is one of the most prominent details that was missing.”
Let’s back up a bit and look at how Brown Dwarfs and Gas Giants are related.
Solar systems are formed from clouds of gas and dust. In the early days of a solar system, one or more stars are formed out of this cloud by gravitational collapse. They ignite with fusion and become the stars we see everywhere in the Universe. The leftover gas and dust forms into planets, or brown dwarfs. This is a simplified version of solar system formation, but it serves our purposes.
In our own Solar System, only a single star formed: the Sun. The gas giants Jupiter and Saturn gobbled up most of the rest of the material. Jupiter gobbled up the lion’s share, making it the largest planet. But what if conditions had been different and Jupiter had kept growing? According to Schlaufman, if it had kept growing to over 10 times the size it is now, it would have become a brown dwarf. But that’s not where the new definition ends.
Metallicity and Chemical Makeup
Mass is only part of it. What’s really behind his new classification is the way in which the object formed. This involves the concept of metallicity in stars.
Stars have a metallicity content. In astrophysics, this means the fraction of a star’s mass that is not hydrogen or helium. So any element from lithium on down is considered a metal. These metals are what rocky planets form from. The early Universe had only hydrogen and helium, and almost insignificant amounts of the next two elements, lithium and beryllium. So the first stars had no metallicity, or almost none.
This is an image of M80, an ancient globular cluster of stars. Since these stars formed in the early universe, their metallicity content is very low. This means that gas giants like Jupiter would be rare or non-existent here, while brown dwarfs are likely plentiful. Image: By NASA, The Hubble Heritage Team, STScI, AURA – Great Images in NASA Description, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6449278
But now, 13.5 billion years after the Big Bang, younger stars like our Sun have more metal in them. That’s because generations of stars have lived and died, and created the metals taken up in subsequent star formation. Our own Sun was formed about 5 billion years ago, and it has the metallicity we expect from a star with its birthdate. It’s still overwhelmingly made of hydrogen and helium, but about 2% of its mass is made of other elements, mostly oxygen, carbon, neon, and iron.
This is where Schlaufman’s study comes in. According to him, we can distinguish between gas giants like Jupiter, and brown dwarfs, by the nature of the star they orbit. The types of planets that form around stars mirror the metallicity of the star itself. Gas giants like Jupiter are usually found orbiting stars with metallicity equal to or greater than our Sun. But brown dwarfs aren’t picky; they form around almost any star. Why?
Brown Dwarfs and Planets Form Differently
Planets like Jupiter are formed by accretion. A rocky core forms, then gas collects around it. Once the process is done, you have a gas giant. For this to happen, you need metals. If metals are present for these rocky cores to form, their presence will be reflected in the metallicity of the host star.
But brown dwarfs aren’t formed by accretion like planets are. They’re formed the same way stars are; by gravitational collapse. They don’t form from an initial rocky core, so metallicity isn’t a factor.
This brings us back to Kevin Schlaufman’s study. He wanted to find out the mass at which point an object doesn’t care about the metallicity of the star they orbit. He concluded that objects above 10 times the mass of Jupiter don’t care if the star has rocky elements, because they don’t form from rocky cores. Hence, they’re not planets akin to Jupiter; they’re brown dwarfs that formed by gravitational collapse.
What Does It Matter What We Call Them?
Let’s look at the Pluto controversy to understand why names are important.
The struggle to accurately classify all the objects we see out there in space is ongoing. Who can forget the plight of poor Pluto? In 2006, the International Astronomical Union (IAU) demoted Pluto, and stripped it of its long-standing status as a planet. Why?
Because the new definition of what a planet is relied on these three criteria:
a planet is in orbit around a star.
a planet must have sufficient mass to assume a hydrostatic equilibrium (a nearly round shape.)
a planet has cleared the neighbourhood around its orbit
The more we looked at Pluto with better telescopes, the more we realized that it did not meet the third criteria, so it was demoted to Dwarf Planet. Sorry Pluto.
Pluto was re-classified as a dwarf planet based on our growing understanding of its nature. Will Schlaufman’s new study help us more accurately classify gas giants and brown dwarfs? NASA’s New Horizons spacecraft captured this high-resolution enhanced color view of Pluto on July 14, 2015. Credit: NASA/JHUAPL/SwRI
Our naming conventions for astronomical objects are important, because they help people understand how everything fits together. But sometimes the debate over names can get tiresome. (The Pluto debate is starting to wear out its welcome, which is why some suggest we just call them all “worlds.”)
Though the Pluto debate is getting tiresome, it’s still important. We need some way of understanding what makes objects different, and names that reflect that difference. And the names have to reflect something fundamental about the objects in question. Should Pluto really be considered the same type of object as Jupiter? Are both really planets in the same sense? The IAU says no.
The same principle holds true with brown dwarfs and gas giants. Giving them names based solely on their mass doesn’t really tell us much. Schlaufman aims to change that.
His new definition makes sense because it relies on how and where these objects form, not simply their size. But not everyone will agree, of course.
A ring of cyclones swirls around Jupiter's south pole. Credit: NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles
In addition to being the largest and most massive planet in our Solar system, Jupiter is also one of its more mysterious bodies. This is certainly apparent when it comes to Jupiter’s powerful auroras, which are similar in some ways to those on Earth. In recent years, astronomers have sought to study patterns in Jupiter’s atmosphere and magnetosphere to explain how aurora activity on this planet works..
For instance, an international team led by researchers from University College London recently combined data from the Juno probe with X-ray observations to discern something interesting about Jupiter’s northern and southern auroras. According to their study, which was published in the current issue of the scientific journal Nature – Jupiter’s intense, Jupiter’s X-ray auroras have been found to pulsate independently of each other.
Jupiter has spectacular aurora, such as this view captured by the Hubble Space Telescope. Credit: NASA, ESA, and J. Nichols (University of Leicester)
As already noted, Jupiter’s auroras are somewhat similar to Earth’s, in that they are also the result of charged particles from the Sun (aka. “solar wind”) interacting with Jupiter’s magnetic field. Because of the way Jupiter and Earth’s magnetic fields are structured, these particles are channeled to the northern and southern polar regions, where they become ionized in the atmosphere. This results in a beautiful light display that can be seen from space.
In the past, auroras have been spotted around Jupiter’s poles by NASA’s Chandra X-ray Observatory and by the Hubble Space Telescope. Investigating this phenomena and the mechanisms behind it has also been one of the goals of the Juno mission, which is currently in an ideal position to study Jupiter’s poles. With every orbit the probe makes, it passes from one of Jupiter’s poles to the other – a maneuver known as a perijove.
For the sake of their study, Dr. Dunn and his team were forced to consult data from the ESA’s XMM-Newton and NASA’s Chandra X-ray observatories. This is due to the fact that while it has already acquired magnificent images and data on Jupiter’s atmosphere, the Juno probe does not have an X-ray instrument aboard. Once they examined the X-ray data, Dr. Dunn and his team noticed a difference between Jupiter’s northern and southern auroras.
Whereas the X-ray emissions at the north pole were erratic, increasing and decreasing in brightness, the ones at the south pole consistently pulsed once every 11 minutes. Basically, the auroras happened independently of each other, which is different from how auroras on Earth behave – i.e. mirroring each other in terms of their activity. As Dr. Dunn explained in a recent UCL press release:
“We didn’t expect to see Jupiter’s X-ray hot spots pulsing independently as we thought their activity would be coordinated through the planet’s magnetic field. We need to study this further to develop ideas for how Jupiter produces its X-ray aurora and NASA’s Juno mission is really important for this.”
The X-ray observations were conducted between May and June of 2016 and March of 2017. Using these, the team produced maps of Jupiter’s X-ray emissions and identified hot spots at each pole. The hot spots cover an area that is larger than the surface area of Earth. By studying them, Dr. Dunn and his colleagues were able to identify patterns of behavior which indicated that they behaved differently from each other.
Naturally, the team was left wondering what could account for this. One possibility they suggest is that Jupiter’s magnetic field lines vibrate, producing waves that carry charged particles towards the poles. The speed and direction of these particles could be subject to change over time, causing them to eventually collide with Jupiter’s atmosphere and generate X-ray pulses.
As Dr Licia Ray, a physicist from Lancaster University and a co-author on the paper, explained:
“The behavior of Jupiter’s X-ray hot spots raises important questions about what processes produce these auroras. We know that a combination of solar wind ions and ions of Oxygen and Sulfur, originally from volcanic explosions from Jupiter’s moon, Io, are involved. However, their relative importance in producing the X-ray emissions is unclear.”
And as Graziella Branduardi-Raymont- a professor from UCL’s Space & Climate Physics department and another co-author on the study – indicated, this research owes its existence to multiple missions. However, it was the perfectly-timed nature of the Juno mission, which has been in operation around Jupiter since July 5th, 2016, that made this study possible.
Composite images from the Chandra X-Ray Observatory and the Hubble Space Telescope show the hyper-energetic x-ray auroras at Jupiter. Credit: X-ray: NASA/CXC/UCL/STScI/W.Dunn et al.
“What I find particularly captivating in these observations, especially at the time when Juno is making measurements in situ, is the fact that we are able to see both of Jupiter’s poles at once, a rare opportunity that last occurred ten years ago,” he said. “Comparing the behaviours at the two poles allows us to learn much more of the complex magnetic interactions going on in the planet’s environment.”
Looking ahead, Dr. Dunn and his team hope to combine X-ray data from XMM-Newton and Chandra with data collected by Juno in order to gain a better understanding of how X-ray auroras are produced. The team also hopes to keep tracking the activity of Jupiter’s poles for the next two years using X-ray data in conjunction with Juno. In the end, they hope to see if these auroras are commonplace or an unusual event.
“If we can start to connect the X-ray signatures with the physical processes that produce them, then we can use those signatures to understand other bodies across the Universe such as brown dwarfs, exoplanets or maybe even neutron stars,” said Dr. Dunn. “It is a very powerful and important step towards understanding X-rays throughout the Universe and one that we only have while Juno is conducting measurements simultaneously with Chandra and XMM-Newton.”
In the coming decade, the ESA’s proposed JUpiter ICy moons Explorer (JUICE) probe is also expected to provide valuable information on Jupiter’s atmosphere and magnetosphere. Once it arrives in the Jovian system in 2029, it too will observe the planet’s auroras, mainly so that it can study the effect these have on the Galilean Moons (Io, Europa, Ganymede and Callisto).
A ring of cyclones swirls around Jupiter's south pole. Credit: NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles
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.
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
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.
