We've been studying Jupiter for a long time, but we still don't understand many things about the gas giant. We think Jupiter formed early on in the solar system, but how did it form? We see belts going in different directions on the surface of Jupiter, but how deep do those belts go? How does the Great Red Spot work? Is there a rocky core at the center of Jupiter?
NASA is trying to find out.
Jupiter crescent image taken by Cassini spacecraft.
Credit: NASA/JPL/University of Arizona
Juno
The Juno mission is managed by NASA's Jet Propulsion Laboratory in collaboration with Southwest Research Institute (SwRI) and Lockheed Martin. The Principal Investigator (PI) of the mission is Dr. Scott Bolton of SwRI.
Credit: NASA/JPL-Caltech
Goal
The goal of Juno is to understand Jupiter's formation, interior, core, and athmosphere. It is doing this by mapping the magnetosphere and studying the temperature, motions, and composition of the Jovian clouds. By understanding how Jupiter formed we can understand how the solar system formed.
Name
The mission is named after Juno, a goddess from Roman mythology. Juno peered through clouds surrounding the god Jupiter to reveal who he truly was.
Selection
Juno is a part of the NASA's New Frontiers program. The New Frontiers program sends medium-cost robotic spacecraft on missions to explore the solar system. It was selected in 2005 after competing for selection with Moonrise, which would have returned samples of lunar regolith to Earth.
Difficulties
Studying Jupiter is tricky because of its radiation belts. Jupiter's powerful magnetosphere creates radiation belts millions of times more powerful than the ones around Earth. Radiation belts can destroy electronics and erase memory.
Mission Facts
Juno launched on August 5th, 2011 at 12:25pm EDT from Cape Canaveral, Florida. The rocket that was used was the Atlas V, which is operated by United Launch Alliance (ULA). The Atlas V variant that was used was the 551, the most powerful version. It has a 5-meter fairing, 5 solid rocket boosters, and a single engine Centaur upper stage.
Image Credit: NASA/Bill Ingalls
It took almost 5 years, an Earth flyby, and two mid-space maneuvers for Juno to arrive at Jupiter.
Throughout Juno's mission the spacecraft is spinning to provide stability.
Image credit: NASA/JPL-Caltech
Juno uses a highly elliptical polar orbit. This allows Juno to avoid the worst of Jupiter’s radiation. A polar orbit goes over the north and south pole of a planet instead of going around the equator. An elliptical orbit has an oval shape, it comes close to a planet and then goes further out into space. This allows for Juno to gather information about Jupiter and then have some time to send all of that data back to Earth. The orbit is designed so that Juno is always able to get solar power from the sun.
The original plan was for Juno to first go into a temporary 53.5 day parking orbit as soon as it arrived at Jupiter, and then lower itself to a 14-day orbit. However, shortly before the maneuver was supposed to happen NASA detected some issues with the propulsion system and decided to cancel the maneuver. They decided to let Juno stay in its 53-day orbit for the remainder of the primary mission. This orbit has ended up benefiting the mission since Juno can now study the outer reaches of the Jupiter system. The spacecraft will also spend more time away from Jovian radiation, which might end up lengthening the mission.
The Perijove is point of Juno's orbit where the spacecraft is closest to Jupiter. Juno mission planners count the number of Perijoves starting with Perijove 1, which was the first close approach after Juno's insertion burn.
Enahnced JunoCam image of Ganymede
Credit: NASA/JPL-Caltech /SwRI/MSSS/Kalleheikki Kannisto (CC BY)
In early 2021, after analyzing the health of the Juno spacecraft, NASA decided to extend Juno's mission to 2025. The extended mission includes the study of something Juno wasn't designed to study, Jupiter's moons. Juno will use multiple flybys of Jupiter's three innermost moons to shorten its orbital period. The first of these close flybys was in June 2021. The extended mission also includes a study of Jupiter's rings and the 'Great Blue Spot', a mysterious gravitational anomaly.
In order to avoid contaminating one of Jupiter’s potentially habitable moons, such as Europa, with bacteria from Earth, Juno will destroy itself at the conclusion of its scientific voyage. At the end of its mission, which is currently scheduled for 2025, Juno will deorbit itself and plunge into the Jovian atmosphere. It will transmit science data back to Earth as it is torn apart by the fierce winds of Jupiter. NASA’s Galileo orbiter ended its mission in a similar way in 2003.
JunoCam image of Jupiter.
Credit: NASA/JPL-Caltech /SwRI/MSSS/Brian Swift (CC-BY)
Mission Milestones
Juno Spacecraft
The Juno spacecraft is designed to minimize cost and power consumption while providing the maximum science return. The spacecraft was built by Lockheed Martin. It has a hexagonal spacecraft bus with three solar arrays and five antennas. The spacecraft is kept stable be being kept in a controlled spin throughout the entire mission.
The Juno spacecraft has three high-efficiency solar array wings that were built by Spectrolab. Juno broke the record for most distant solar-powered spacecraft on January 16th, 2016 when it beat the record set by ESA's Rosetta spacecraft. Juno was 793 million kilometers (493 million miles) from the sun.
Photo credit: NASA/Jack Pfaller
The Juno spacecraft a few weeks before launch. At the top of the image the High Gain Antenna (HGA) can be prominently seen. The HGA is its main antenna. The circular antenna has a diameter of 2.5 meters (8 feet). The HGA was built by ATK Space Systems, which is now owned by Northrop Grumman. The outside if the antenna is covered in silver insulating blankets that protect the antenna from the sunlight.
Beneath the HGA the electronics vault can be seen. Many of the scientific sensors are placed on the top deck next to the electronics vault.
Photo credit: NASA
Power
Jupiter receives only 1/25th the amount of sunlight that the Earth receives. Because of this, all spacecraft before Juno that have traveled to Jupiter have had to use a Radioisotope Thermoelectric Generator (RTG). RTGs use heat created by nuclear isotopes to generate electricity. They are extremely reliable, but are very expensive.
Instead of using an RTG, Juno uses solar panels. It is able to do this because of recent improvements in solar panel technology and smart mission planning.
Propulsion
Juno has two interconnected propulsion systems.
A large main engine that is used for major events, like the Jupiter Insertion burn, and a set of small thrusters. The small thrusters are used to adjust it's orbit, change it's spin rate, and perform small tweaks to its trajectory.
Hydrazine and nitrogen tetroxide are stored in large tanks inside Juno's spacecraft bus. The small thrusters use just hydrazine, while the main engine uses both propellants.
Communication
Juno's 5 antennas that each serve a different purpose. The HGA is the largest and most visible antenna it can transmit more information than the other antennas, but requires a larger dish and more precise pointing. A Medium Gain Antenna (MGA) and three Low Gain Antennas (LGAs) pointed in different directions allow for Juno to communicate with Earth no matter what direction it is pointed.
Electronics
The powerful radiation belts that Juno is studying pose a major threat to its electronics. Which is why engineers built a vault to keep all of the electronics safe. This titanium electronics box shield the computers that control the spacecraft from powerful x-rays and charged particles. The electronics box is placed on top of the spacecraft bus beneath the HGA.
Scientific Instruments
The Juno spacecraft is packed with 9 science instruments. Together they have provided a wealth of scientific data that has changed our understanding of Jupiter. Each perijove pass the Juno spacecraft is either performing Gravity Science or using its Microwave Radiometer. The main limiting factor for data collection is the amount of data that Juno can transmit.
Jovian InfraRed Auroral Mapper (JIRAM) | INAF
JIRAM is an infrared camera and spectrometer attached to the bottom of the Juno spacecraft. The camera takes images of the heat being emitted by the planet, while the spectrometer splits the infrared light that it receives into different wavelengths to determine the composition of Jupiter. This data is used to study the Jovian aurora, which helps us study the magnetosphere.
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JunoCam | MSS
JunoCam is a small color camera designed to image the Jovian cloud tops. It was not originally designed as a scientific instrument, but as a way to engage the public by allowing ordinary people to process and colorize JunoCam images. Professional and amateur scientists have found JunoCam very useful for science.
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UltraViolet imaging Spectrograph (UVS) | SwRI and BELSPO
UVS works similar to JADE, but with ultraviolet light. It splits UV light into different frequencies to image Jupiter's auroras at different frequencies.
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Magnetometer (MAG) | GSFC and DTU
At the end of one of Juno’s solar arrays is a metal triangle that contains two magnetometers. These magnetometers are placed far away from the rest of the spacecraft so that the magnetic fields produced by Juno’s electronics don’t interfere with the data collected about the orientation and strength of the Jovian magnetic field.
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Jupiter Energetic particle Detector Instrument (JEDI) | APL
JEDI works with JADE to study charged particles. By analyzing energetic charged particles JEDI teaches us how Jupiter’s magnetosphere interacts with particles and creates auroras and radiation belts.
Jovian Auroral Distributions Experiment (JADE) | SwRI
JADE studies Jupiter’s aurora by detecting electrons and positively charged particles. The JADE experiment consists of three electron detectors spaced 120 degrees apart and a single ion sensor. These sensors detect less energetic particles than JEDI.
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Microwave Radiometer (MWR) | JPL
In order to probe the interior of Jupiter Juno has six antennas that detect the microwave radiation being emitted by Jupiter. They are each a different size and can detect microwave radiation being emitted at a different cloud level.
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Waves | University of Iowa
The Waves experiment measures plasma waves using two long antennae that form a V and a small magnetic coil. Scientists use this data to understand the magnetic field, or magnetosphere of Jupiter.
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Gravity Science | JPL and ASI
As Juno makes close approaches its orbital speed and position are altered by the Jovian gravity. These tiny fluctuations can be detected by measuring the doppler shift of the radio signals being transmitted by Juno.
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The Juno spacecraft being prepared for launch. The largest of the six microwave antennas can be seen on the front of the spacecraft. The magnetometer is folded up on the left side of the spacecraft. Other science instruments are attached to the upper deck on the top of the spacecraft.
Credit: NASA/JPL-Caltech
This artistic rendering shows the magnetic field of Jupiter. The magnetic field traps charged particles around Jupiter. These charged particles create the radiation belts, and can be measured by JADE and JEDI. It also creates the aurora at Jupiter's poles. These aurora are imaged by JIRAM and UVS. By studying the magnetosphere the core of Jupiter can be studied.
Credit: NASA's Goddard Space Flight Center
Abbreviated Locations:
APL - John Hopkins University Applied Physics Laboratory: A research center in Maryland connected with John Hopkins University
ASI - Agenzia Spaziale Italiana (Italian Space Agency): The national space agency of Italy; one of the most experienced space agencies in the world
BELSPO - Belgian Science Policy Office: Belgian government body that leads research in the country
GSFC - Goddard Space Flight Center: One of NASA’s largest centers; it specializes in robotic spacecraft and scientific research.
DTU - Danmarks Tekniske Universitet (Technical University of Denmark): A leading engineering university in Denmark
INAF - Istituto Nazionale di Astrofisica (National Institute for Astrophysics): An Italian research center for astronomy and astrophysics
MSSS - Malin Space Science Systems: A company that build advanced cameras for spacecraft
SwRI - Southwest Research Institute: An independent non-profit research organization
Discoveries
The Juno spacecraft has made many discoveries about Jupiter. It has upended existing theories about the formation of Jupiter. Even though it has answered many mysteries about Jupiter, it has also discovered new questions that need answering.
Magnetosphere
By studying the auroras and combining that with data from Juno’s magnetometer scientists discovered that the magnetic field of Jupiter is asymmetrical and uneven. Near the equator there is a strong, mysterious magnetic anomaly, the Great Blue Spot (GBS). For reasons that are yet to be understood, the magnetic field slowly changes over time, while the GBS slowly moves with the Jovian winds. This is very different from the Earth’s magnetosphere which is more simple, orderly, and consistent.
Aurora
Juno discovered that Jupiter’s polar aurora are powerful and chaotic. Juno discovered that the Jovian aurora are up to 30 times as strong as the ones on Earth. Juno also discovered that some aurora storms form on the nightside of Jupiter and then become “dawn storms” when they reach the day side of Jupiter. This is similar to some phenomena that have been observed on Earth. Juno has also helped us understand that Io, Europa, and Jupiter's moons influence the magnetosphere and create small aurora storms.
Interior
By examining Jupiter in ultraviolet, visible, infrared, and microwave wavelengths, Juno made multiple discoveries about the structure and interior of Jupiter. Scientists discovered that Jupiter's red and white belts extend about 3,200 kilometers into Jupiter. It also found that the famous Great Red Spot extends at least 350 kilometers down. Juno also discovered clusters of huge cyclones spinning at the North and South Poles of Jupiter, and that the different chemicals within Jupiter aren't evenly mixed. Juno has found multiple similarities between Jupiter's gaseous clouds and Earth's oceans.
Core
Juno’s discoveries have disproved all existing theories about the interior of Jupiter, and scientists have been truly surprised. Scientists have found that the core of Jupiter isn't solid, but is “fuzzy.” It is not clearly defined and is thought to be made of hydrogen under extremely high pressure mixed with pieces of rock. Unfortunately, we don’t understand how hydrogen acts at extreme pressures, so we don’t understand the physics occurring in the deep interior of Jupiter. Having such a unique planetary core is probably one of the main reasons why Jupiter's magnetic field is so wonky.
A composite of two images by the Hubble Space Telescope showing the auroras that constantly exist around the Jovian poles. The only planets in our solar system with powerful aurora are Earth, Jupiter, Saturn, Uranus, and Neptune. Juno has allowed us to study the aurora of Jupiter up close, something that has only been done around Earth. This helps us understand the aurora on our home planet by finally giving us something to compare them to.
Credits: NASA/ESA/J. Nichols (University of Leicester)
This infrared image by JIRAM shows the cyclones at Jupiter's South Pole in 2019. In 2017 Juno observed 6 cyclones here, with one in the center. In 2019 another, smaller, cyclone (bottom right) was beginning to appear. But this smaller storm was eventually pushed out and the cyclones went back to a pentagon formation.
Photo credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM
Juno used its magnetometer to map the magnetosphere of Jupiter. This 3D visualization shows how the magnetic field is chaotic and disorganized. The great blue spot, which can be seen near the center of the image, is an anomaly near the equator where there is a strong negative magnetic force.
Photo credit: NASA/JPL-Caltech/Harvard/Moore et al.
Zodiacal light is a faint glowing column that appears at night. Juno made the unexpected discovery of the origin of this light. While flying to Jupiter, Juno’s solar arrays and star-tracking cameras acted like a giant dust detector. Scientists used this data to find evidence that the origin of this light is a cloud of dust that originates from Mars.
Photo credit: ESO/Y. Beletsky via Wikimedia Commons
Conclusion
Juno is one of NASA’s most successful missions. Using a small budget of $1.1 billion it has performed science equivalent of a Flagship mission. The discoveries are still rolling in and Juno will continue to reshape our understanding of Jupiter, and the solar system's formation. Juno has also left many things unexplained, which is the paradox of exploration. For everything we discover, we find more mysteries that need answers.
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Over the next few years two life hunting robotic missions, JUICE and Europa Clipper, are scheduled to launch to Jupiter. They won’t focus on Jupiter, but instead on its icy moons: Europa, Callisto, and Ganymede. Juno has helped lay a foundation for these missions, by studying the physical and geological processes that affect these moons. These processes play a big impact on the biological processes that may be going on beneath the moon's icy surfaces.
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Some of Juno’s discoveries are helping us better understand Earth. By seeing how the magnetosphere, radiation belts, and winds of Jupiter work, we can understand similar processes on Earth better, and by extension, planets around other stars. As we continue to understand the planets in our solar system we will find patterns that can also apply to other star systems. By understanding how Jupiter makes a moon like Europa potentially habitable, we can predict whether life can be on planets or moons light years away from us.