NASA releases a variety of photos and videos observing the vast universe every 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. This is already the third time in January that Jupiter has appeared as the Astronomy Picture of the Day. Why do scientists have such a special fondness for 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 by the United States, Europe and Canada over 25 years at a cost of 13 trillion won. Launched into space on Christmas 2021, it reached its observation point 1.5 million kilometers from Earth in Jan. the following year. Equipped with a 6.5-meter-diameter primary mirror, James Webb is the largest of any astronomical telescope ever launched and 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 images, the dim-looking Jupiter shows auroras shining brightly at the 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 over 650 kilometers per hour. The Great Red Spot, which for centuries was more than three times the size of Earth, has shrunk sideways in recent years to become similar in size to Earth.
Faint stripes around Jupiter are also visible in the image. The auroras and moons are so bright that their light is distorted around the James Webb telescope. This is the diffraction phenomenon, in which waves such as light, sound, or water waves, when encountering an obstacle or a narrow slit, spread around the edges or bend behind the slit. The image shows elongated diffraction patterns from the auroras and the moon Io.
This image also clearly shows the Jovian moons Amalthea and Adrastea. The number of known Jovian moons is 95. With the addition of 12 moons in Feb. 2023, Jupiter overtook Saturn to become the planet with the most moons in the solar system. Io, Europa, Ganymede and Callisto—so-called Galilean moons discovered around Jupiter by Italian scientist Galileo Galilei in 1610—are the largest.
◇ Massive storms driven by east–west winds
Jupiter is a giant gas planet 11 times Earth's diameter and 300 times heavier. 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 all other bodies in the solar system combined—planets, asteroids and comets.
Its rotation and orbital speeds contrast sharply with Earth's. Jupiter is five times farther from the sun than Earth, taking 12 years to orbit it. In other words, one Jovian year equals 12 Earth years. But its rotation is very fast, making one Jovian day just 10 hours on Earth.
NASA also released an infrared image of Jupiter observed by James Webb on the 10th. As usual, clouds in Jupiter's atmosphere are roiling. Jupiter was at opposition to the sun, making it the closest and brightest for observation from Earth.
The image taken three days before the 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. In particular, two smaller red spots are visible—one at the top of the northernmost region and the other near the south pole.
The clouds seen in images of Jupiter are mostly composed of ammonia and hydrogen sulfide. Water clouds can be found deep in the atmosphere. The planet's signature stripes are created by strong east–west winds in the upper atmosphere. Within them are storms that last for years. The orange stripes are the descending regions, called belts. The rising bright regions are called zones. The two flow in opposite directions, eastward and westward, respectively.
◇ The strongest magnetic field in the solar system
Given its size and composition, Jupiter is thought to be the first planet to have formed in the solar system. True to its role as the eldest, it protects its siblings with powerful gravity and a magnetic field. Even if 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's magnetic field is 14 to 20 times stronger than Earth's at the surface, and in total energy amounts to 18,000 to 20,000 times Earth's. A magnetic field is the space where magnetic force—the force by which a magnet or electric current attracts or repels objects—acts. With such a powerful magnetic field, Jupiter also blocks the solar wind, a stream 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 mechanism. It is explained by the so-called dynamo theory. Just as an electromagnet with a wound coil rotates inside a generator to change the magnetic field and produce current, ferromagnetic material melted in Earth's outer core rotates with the planet's spin to create induced currents. The resulting current in turn generates a magnetic field according to Faraday's law of electromagnetic induction. Repeating this process gives rise to a magnetic field.
What differs about Jupiter's magnetic field from Earth's is the material that rotates. On Earth, convection of molten iron and nickel in the outer core generates the magnetic field. By contrast, on Jupiter, liquid metallic hydrogen rotates to create the field.
We usually think of hydrogen as a gas, but on Jupiter the immense 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, the swirling ocean of liquid metallic hydrogen generates powerful currents and a magnetic field.
◇ High-resolution Jupiter clouds captured by the Juno probe
Since the 1970s, NASA has been sending unmanned probes to observe Jupiter. Voyager 1, now out to the outer reaches of the solar system, discovered three thin rings made of fine dust particles at Jupiter in 1979. After the Jupiter probe Galileo launched into space and operated until 2003, Juno launched on Aug. 5, 2011, and arrived in Jupiter's 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 in the south more than in the north. Radio observations by Juno revealed that Jupiter's atmosphere is clearly structured down to depths of hundreds of kilometers below the upper clouds.
The Juno probe explored Jupiter's moon Ganymede in 2021 and the following year closely observed the valleys and impact craters on Europa's surface. Juno's Europa findings will provide useful data for the Europa Clipper probe that NASA launched in Nov. 2024. Clipper is scheduled to arrive in Jupiter's orbit in 2030.
Europa, along with Saturn's moon Enceladus, is considered one of the most likely bodies to have an ocean capable of supporting life beneath a thick icy crust. The goal of Europa Clipper is to approach to within 26 kilometers above Europa's surface to take high-resolution images and analyze its chemical composition. This will help determine whether it can support life.