Jupiter: a massive, lifeless gas giant out there on the other side of the asteroid belt. It’s a behemoth, containing 2.5 times as much mass as all the other planets combined. To top it off, it’s named after the Roman God of War.
Earth: a tiny rocky world, almost too close to the Sun, where life rises and falls, punctuated repeatedly by extinctions. Compared to Jupiter, it’s a gum-drop world: Jupiter is 317.8 times the mass of Earth. And Earth is named after a goddess in German paganism, or so we think.
“Out of all the complexity flows beauty…”
Norman Kuring, NASA’s Goddard Space Flight Center.
Jeff Morgenthaler, a senior scientist at the Planetary Science Institute, likes to think of himself as an experimental physicist whose laboratory opens to the sky. He has used a comet to measure the ionization lifetime of carbon, is using Io’s atmosphere as a probe of conditions in Jupiter’s magnetosphere and has constructed a small-aperture coronagraph to monitor measure Jupiter’s magnetospheric response to a large volcanic eruption on Io.
Thanks to a mission extension, NASA’s Juno probe continues to orbit Jupiter, being only the second spacecraft in history to do so. Since it arrived around the gas giant on July 5th, 2016, Juno has managed to gather a great deal of information on Jupiter’s atmosphere, magnetic and gravity environment, and its interior structure.
In that time, the probe has also managed to capture some breathtaking images of Jupiter as well. But on December 21st, during the probe’s sixteenth orbit of the gas giant, the Juno probe changed things up when four of its cameras captured images of the Jovian moon Io, showcasing its polar regions and spotting what appeared to be a volcanic eruption.
What would it be like to be onboard the Cassini orbiter as it made its way around Jupiter and Saturn and their moons? Pretty cool. Now a new video made from Cassini images pieces together parts of that stately journey.
Jupiter’s moon Europa has been the subject of fascination ever since the Pioneer 10 and 11 and Voyager1 and 2 missions passed through the system back in the 1970s. While the moon has no viable atmosphere and is bombarded by intense radiation from Jupiter’s powerful magnetic field, scientists believe that one of the most likely places to find life beyond Earth exists beneath its icy surface.
Little wonder then why multiple missions are being planned to study this moon up-close. However, if and when those missions reach Europa sometime in the next decade, they will have to contend with some sharp surface features that could make it hard to land. Such is the conclusion of a new study by researchers from Britain, the US and NASA’s Ames Research Center, which indicates that Europa’s surface is covered in bladed terrain.
For almost 200 years humans have been watching the Great Red Spot (GRS) on Jupiter and wondering what’s behind it. Thanks to NASA’s Juno mission, we’ve been getting better and better looks at it. New images from JunoCam reveal some of the deeper detail in our Solar System’s longest-lived storm.
In July of 2016, the Juno spacecraft established orbit around Jupiter, becoming the first spacecraft since the Galileoprobe to study the planet directly. Since that time, the probe has been sending back vital information about Jupiter’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 exciting things about this gas giant. Continue reading “Another Juno Flyby, Another Amazing Sequence of Images of Jupiter”
The gas giant Jupiter, which was named in honor of the king of the gods in the Roman pantheon, has always lived up to its name. In addition to being the largest planet in the Solar System – with two and a half times the mass of all the other planets combined – it also has an incredibly powerful magnetic field and the most intense storms of any planet in the Solar System.
What’s more, it is home to some of the largest moons in the Solar System (known as the Galilean Moons), and has more known moons than any other planet. And thanks to a recent survey led by Scott S. Sheppard of the Carnegie Institution of Science, twelve more moons have been discovered. This brings the total number of known moons around Jupiter to 79, and could provide new insight into the history of the Solar System.
The team was led by Scott S. Sheppard and included Dave Tholen (University of Hawaii) and Chad Trujillo (Northern Arizona University). It was this same team that first suggested the existence of a massive planet in the outer reaches of the Solar System (Planet 9 or Planet X) in 2014, based on the unusual behavior of certain populations of extreme Trans-Neptunian Objects (eTNOs).
Curiously enough, it was while Sheppard and his colleagues were hunting for this elusive planet that they spotted the first of these new moons in 2017. As Sheppard explained in a recent Carnegie press release:
“Jupiter just happened to be in the sky near the search fields where we were looking for extremely distant Solar System objects, so we were serendipitously able to look for new moons around Jupiter while at the same time looking for planets at the fringes of our Solar System.”
The orbits of the newly-discovered moons were then calculated by Gareth Williams of the International Astronomical Union’s Minor Planet Center (MPC), based on the team’s observations. “It takes several observations to confirm an object actually orbits around Jupiter,” he said. “So, the whole process took a year.”
As you can see from the image above, two of the newly-discovered moons (indicated in blue) are part of the inner group that have prograde orbits (i.e. they orbit in the same direction as the planet’s rotation). They complete a single orbit in a little less than a year, and have similar orbital distances and angles of inclination. This is a possible indication that these moons are fragments of a larger moon that was broken apart, possibly due to a collision.
Nine of the new moons (indicated in red) are part of the distant outer group that have retrograde orbits, meaning they orbit in the opposite direction of Jupiter’s rotation. These moons take about two years to complete a single orbit of Jupiter and are grouped into three orbital groups that have similar distances and inclination. As such, they are also thought to be remnants of three larger moons that broke apart due to past collisions.
The team observed one other moon that does not fit into either group, and is unlike any known moon orbiting Jupiter. This “oddball moon” is more distant and more inclined than the prograde moons and takes about one and a half years to orbit Jupiter, which means its orbit crosses the outer retrograde moons. Because of this, head-on collisions are much more likely to occur with the retrograde moons, which are orbiting in the opposite direction.
The orbit of this oddball moon was also confirmed by Bob Jacobson and Marina Brozovic at NASA’s Jet Propulsion Laboratory in 2017. This was motivated in part to ensure that the moon would not be lost before it arrived at the predicted location in its orbit during the recovery observations made in 2018. As Sheppard explained,
“Our other discovery is a real oddball and has an orbit like no other known Jovian moon. It’s also likely Jupiter’s smallest known moon, being less than one kilometer in diameter…This is an unstable situation. Head-on collisions would quickly break apart and grind the objects down to dust.”
Here too, the team thinks that this moon could be the remains of a once-larger moon; in this case, one that had a prograde orbit that formed some of the retrograde moons through past collisions. The oddball moon already has a suggested name for it – Valetudo, after the Jupiter’s great-granddaughter, the goddess of health and hygiene in the Roman pantheon.
In addition to adding to Jupiter’s overall moon count, the study of what shaped these moon’s orbital histories could teach scientists a great deal about the earliest period of the Solar System. For instance, the fact that the smallest moons in Jupiter’s various orbital groups (prograde, retrograde) are still abundant suggests that the collisions that created them occurred after the era of planet formation.
According to the Nebular Hypothesis of Solar System formation, the Sun was still surrounded by a rotating protoplanetary disk at this time – i.e. the gas and dust from which the planets formed. Because of their sizes – 1 to 3 km – these moons would have been more influenced by surrounding gas and dust, which would have placed a drag on their orbits and caused them to fall inwards towards Jupiter.
The fact that these moons still exist shows that they likely formed after this gas and dust dissipated. In this respect, these moons are much like time capsules or geological records, preserving pieces of Jupiter’s (and the Solar Systems) history of formation and evolution.
When the Juno spacecraft arrived in orbit around Jupiter in 2016, it became the second spacecraft in history to study Jupiter directly – the first being the Galileo probe, which orbited Jupiter between 1995 and 2003. With every passing orbit (known as a perijove, which take place every 53 days), the spacecraft has revealed more about Jupiter’s atmosphere, weather patterns, and magnetic environment.
In addition, Juno recently discovered something interesting about Jupiter’s closest orbiting moon Io. Based on data collected by its Jovian InfraRed Auroral Mapper (JIRAM) instrument, Juno detected a new heat source close to the south pole of Io that could indicate the presence of a previously undiscovered volcano. This is just the latest discovery made by the probe during its mission, which NASA recently extended to 2021.
The infrared data was collected on Dec. 16th, 2017, when the Juno spacecraft was about 470,000 km (290,000 mi) away from Io. As Alessandro Mura, a Juno co-investigator from the National Institute for Astrophysics (INAF) in Rome, explained in a recent NASA press release:
“The new Io hotspot JIRAM picked up is about 200 miles (300 kilometers) from the nearest previously mapped hotspot. We are not ruling out movement or modification of a previously discovered hot spot, but it is difficult to imagine one could travel such a distance and still be considered the same feature.”
Aside from Juno and Galileo, many NASA missions have visited or passed through the Jovian System in the past few decades. These have including the Pioneer 10 and 11 missions in 1973/74, the Voyager 1 and 2 missions in 1979, and the Cassini and New Horizons missions in 2000 and 2007, respectively. Each of these missions managed to snap pictures of the Jovians moons on their way to the outer Solar System.
Combined with ground-based observations, scientists have accounted for over 150 volcanoes on the surface of Io so far, with estimates claiming there could over 400 in total. Since it entered Jupiter’s orbit on July 4th, 2016, the Juno probe has traveled nearly 235 million km (146 million mi) from one pole to other. On July 16th, Juno will conduct its 13th perijove maneuver, once again passing low over Jupiter’s cloud tops at a distance of about 3,400 km (2,100 mi).
During these flybys, Juno probes beneath the upper atmosphere to study the planet’s auroras to learn more about it’s structure, atmosphere and magnetosphere. By shedding light on these characteristics, the Juno probe will also teach us more about the planet’s origins and evolution. This in turn will teach scientists a great deal more about the formation and evolution of our Solar System, and perhaps how life began here.
In the 1970s, the Jupiter system was explored by a succession of robotic missions, beginning with the Pioneer 10 and 11 missions in 1972/73 and the Voyager 1 and 2 missions in 1979. In addition to other scientific objectives, these missions also captured images of Europa’s icy surface features, which gave rise to the theory that the moon had an interior ocean that could possibly harbor life.
Since then, astronomers have also found indications that there are regular exchanges between this interior ocean and the surface, which includes evidence of plume activity captured by the Hubble Space Telescope. And recently, a team of NASA scientists studied the strange features on Europa’s surface to create models that show how the interior ocean exchanges material with the surface over time.
The study, which recently appeared in the the Geophysical Research Letters under the title “Band Formation and Ocean-Surface Interaction on Europa and Ganymede“, was conducted by Samuel M. Howell and Robert T. Pappalardo – two researchers from the NASA Jet Propulsion Laboratory. For their study, the team examined both Ganymede and Europa to see what the moons surface features indicated about how they changed over time.
Using the same two-dimensional numerical models that scientists have used to solve mysteries about motion in the Earth’s crust, the team focused on the linear features known as “bands” and “groove lanes” on Europa and Ganymede. The features have long been suspected to be tectonic in nature, where fresh deposits of ocean water have risen to the surface and become frozen over previously-deposited layers.
However, the connection between this band-forming processes and exchanges between the ocean and the surface has remained elusive until now. To address this, the team used their 2-D numerical models to simulate ice shell faulting and convection.Their simulations also produced a beautiful animation that tracked the movement of “fossil” ocean material, which rises from the depths, freezes into the base of the icy surface, and deforms it over time.
Whereas the white layer at the top is the surface crust of Europa, the colored band in the middle (orange and yellow) represents the stronger sections of the ice sheet. Over time, gravitational interactions with Jupiter cause the ice shell to deform, pulling the top layer of ice apart and creating faults in the upper ice. At the bottom is the softer ice (teal and blue), which begins to churn as the upper layers pull apart.
This causes water from Europa’s interior ocean, which is in contact with the softer lower layers of the icy shell (represented by white dots), to mix with the ice and slowly be transported to the surface. As they explain in their paper, the process where this “fossil” ocean material becomes trapped in Europa’s ice shell and slowly rises to the surface can take hundreds of thousands of years or more.
As they state in their study:
“We find that distinct band types form within a spectrum of extensional terrains correlated to lithosphere strength, governed by lithosphere thickness and cohesion. Furthermore, we find that smooth bands formed in weak lithosphere promote exposure of fossil ocean material at the surface.”
In this respect, once this fossil material reaches the surface, it acts as a sort of geological record, showing how the ocean was millions of years ago and not as it is today. This is certainly significant when it comes to future missions to Europa, such as NASA’s Europa Clipper mission. This spacecraft, which is expected to launch sometime in the 2020s, will be the first to study Europa exclusively.
In addition to studying the composition of Europa’s surface (which will tell us more about the composition of the ocean), the spacecraft will be studying surface features for signs of current geological activity. On top of that, the mission intends to look for key compounds in the surface ice that would indicate the possible presence of life in the interior (i.e. biosignatures).
If what this latest study indicates is true, then the ice and compounds the Europa Clipper will be examining will essentially be “fossils” from hundreds of thousands or even millions of years ago. In short, any biomarkers the spacecraft detects – i.e. signs of potential life – will essentially be dated. However, this need not deter us from sending missions to Europa, for even evidence of past life would be groundbreaking, and a good indication that life still exists there today.
If anything, it makes the case for a lander that can explore Europa’s plumes, or perhaps even a Europa submarine (cryobot), all the more necessary! If there is life beneath Europa’s icy surface, we are determined to find it – provided we don’t contaminate it in the process!