NASA releases a different photo or video of the vast universe observed each day as the Astronomy Picture of the Day. On the 18th (local time), NASA released a high-resolution infrared image of Jupiter taken by the James Webb Space Telescope. Jupiter has already appeared as the astronomy picture of the day for the third time in January alone. Why do scientists particularly favor Jupiter among the many planets in the solar system? What about Jupiter has captivated scientists?
◇ Auroras at the poles and the Great Red Spot stand out
The James Webb Space Telescope is the largest space telescope ever built, developed over 25 years by the United States, Europe, and Canada at a cost of 13 trillion won. It was launched into space on Christmas 2021 and arrived the following January at its observation point 1.5 million kilometers from Earth. James Webb is equipped with a 6.5-meter primary mirror, making it the largest astronomical telescope ever launched, and it can collect more than six times as much light as the Hubble Space Telescope.
This time, the James Webb Space Telescope captured Jupiter in infrared wavelengths. Unlike transfer photos, the dim-looking Jupiter shows auroras shining brightly at the north and south poles and the Great Red Spot below the equator. The Great Red Spot is a high-pressure storm in Jupiter's southern hemisphere that rotates counterclockwise at speeds exceeding 650 kilometers per hour. The Great Red Spot, which for centuries was more than three times the size of Earth, has shrunk horizontally in recent years to become similar in size to Earth.
The photo also shows faint stripes around Jupiter. The auroras and moons are so bright that their light is distorted around the James Webb Telescope. This is diffraction, a wave phenomenon in which waves such as light, sound, or water bend around edges or spread into the region behind a narrow opening when they encounter an obstacle or slit. In the image, the diffraction patterns from the auroras and the moon Io appear elongated.
The latest image also clearly shows Amalthea and Adrastea, moons of Jupiter. The number of known Jovian moons stands at 95. In Feb. 2023, 12 more moons were added, allowing Jupiter to overtake Saturn as the planet with the most moons in the solar system. In 1610, Italian scientist Galileo Galilei discovered Io, Europa, Ganymede, and Callisto around Jupiter, the so-called Galilean moons, which are the largest.
◇ Massive storms created by east-west winds
Jupiter is a giant gas planet with a diameter 11 times that of Earth and 300 times its mass. Its composition, like the sun's, is mostly hydrogen and helium. Excluding the sun, the material that makes up Jupiter is twice as much as the total of all other bodies in the solar system—planets, asteroids, and comets combined.
Its rotation and revolution speeds contrast sharply with Earth's. Jupiter is five times farther from the sun than Earth is, taking 12 years to orbit the sun. In other words, one year on Jupiter equals 12 years on Earth. But it rotates very quickly, so a day on Jupiter is only 10 hours on Earth.
NASA also released an infrared image of Jupiter taken by James Webb on the 10th. As usual, clouds in Jupiter's atmosphere appear to be churning. With Jupiter at opposition to the sun, it was at its closest and brightest for observation from Earth.
The image taken three days before its release also showed the Great Red Spot south of the equator clearly along with the cloud bands. Although the Great Red Spot is said to be shrinking, it is still about the size of Earth. Notably, two smaller red spots are visible—one at the top of the northernmost region and the other near the south pole.
Most of the clouds seen in images of Jupiter are composed of ammonia and hydrogen sulfide. Water clouds are found much deeper in the atmosphere. Jupiter's signature stripes are created by strong east-west winds in the upper atmosphere. Within them are storms that last for years. The orange bands are descending regions, called belts in English. The rising, bright regions are called zones. The two flow in opposite directions, eastward and westward, respectively.
◇ The most powerful magnetic field in the solar system
Based on its size and composition, Jupiter is thought to be the first planet to have formed in the solar system. True to its status as the eldest, it protects its siblings with strong gravity. Even when an asteroid wandering through space heads toward Earth, it is likely to be captured en route by Jupiter's gravity, which is 2.5 times stronger than Earth's.
Jupiter also has a powerful magnetic field. At the surface it is 14 to 20 times that of Earth, and in total energy it reaches 18,000 to 20,000 times Earth's. A magnetic field is the space in which magnetic force—the pull or push exerted by a magnet or electric current—acts. With such a powerful magnetic field, Jupiter blocks the solar wind, the flow of high-energy particles.
Why is Jupiter's magnetic field stronger than Earth's? For starters, Earth and Jupiter generate magnetic fields by the same principle. It is explained by the so-called dynamo theory. Just as a coil-wound electromagnet rotating inside a generator changes the magnetic field to produce an electric current, magnetic materials melted in Earth's outer core rotate with the planet's spin to create induced currents. The generated currents in turn produce a magnetic field, as described by Faraday's law of electromagnetic induction. Repeating this process gives rise to a magnetic field.
What differs in Jupiter's magnetic field from Earth's is the material that rotates. On Earth, iron and nickel melted in the outer core generate the magnetic field through convective rotation. In contrast, on Jupiter, liquid metallic hydrogen rotates to create the magnetic field.
When we think of hydrogen, we usually think of a gas, but on Jupiter, enormous atmospheric pressure compresses hydrogen into a liquid. At about one-third of the way down into Jupiter's atmosphere, hydrogen becomes a liquid that conducts electricity like a metal. As Jupiter spins at tremendous speed, its swirling ocean of liquid metallic hydrogen generates powerful currents and a magnetic field.
◇ High-resolution Jupiter clouds captured by the Juno probe
NASA has been sending unmanned probes to observe Jupiter since the 1970s. Voyager 1, which has now traveled to the outer reaches of the solar system, discovered three faint rings made of fine dust particles at Jupiter in 1979. After the Jupiter probe Galileo launched in 1987 and operated until 2003, Juno was launched on Aug. 5, 2011, and arrived in Jovian orbit on July 5, 2016.
On the 6th, NASA released images of Jupiter taken by Juno. With this observation, Juno found that Jupiter is far more complex than expected. Earth's magnetic field is a dipole with N and S poles like a bar magnet, but Jupiter was different. In particular, it was found to have multiple poles near the south pole rather than the north. According to Juno's radio observations, Jupiter's atmosphere is distinct down to hundreds of kilometers below the upper cloud deck.
The Juno probe explored Ganymede in 2021 and the following year closely observed Europa's surface valleys and impact craters. Juno's findings on Europa will provide useful data for the Europa Clipper probe that NASA launched in Nov. 2024. Clipper is scheduled to arrive in Jovian orbit in 2030.
Europa, along with Saturn's moon Enceladus, is considered one of the most likely worlds to have an ocean capable of supporting life beneath a thick icy crust. Europa Clipper's goal is to approach as close as 26 kilometers above Europa's surface to take high-resolution images and analyze its chemical composition. Through this, it will determine whether the moon could support life.