Jupiter Discovery

After five years of flight, on July 4, 2016, the “Juneau” Jupiter probe successfully entered the orbit of Jupiter. Its mission not only to detect the atmospheric environment of this giant gaseous planet at close range, but also to Jupiter Further exploration inside the atmosphere. It is expected that by July 2021, the “Juneo” will complete its exploration mission and fall into Jupiter. Today, before the fall, the Juno has made a number of scientific discoveries about Jupiter. These new knowledge have largely refreshed scientists’ understanding of Jupiter and its moons.

“Juno” Jupiter probe.

Mission review
Before the official exploration began, the “Juneo” had already broken two world records: it was the farthest solar-powered probe launched by mankind and the fastest-flying probe (on the day of reaching Jupiter, the “Juneo” It is accelerated to 265,000 kilometers per hour under the huge gravity of Jupiter).

The “Juneau” carried nine major instruments, including microwave radiometers, infrared imaging spectrometers, gravity/radio research equipment, vector magnetometers and color cameras. Microwave radiometers and infrared imaging spectrometers are used to detect thermal radiation from the depths of Jupiter’s atmosphere. Other instruments detect Jupiter’s gravitational field, polarity, and magnetosphere. Its three solar array wings with huge stretches are responsible for stabilization. And power the aircraft.

Jupiter “Water Mystery”
Planetary scientists have always worked to figure out how much water is in Jupiter’s atmosphere. Jupiter is considered to be the first planet to be formed in the solar system. It captures a large amount of gas and dust that is not absorbed by the sun. Water has an important influence on the planet’s atmosphere and internal structure. Knowing the content of water helps to further clarify the mystery of the formation and evolution of giant planets in the early formation of the solar system. In December 1995, a small probe released by the Jupiter probe “Galileo” entered the atmosphere of Jupiter. The water content measured at a depth of about 120 kilometers from the surface of Jupiter was only 1/10 of the previously predicted value. Scientists therefore believe that Jupiter has a low proportion of hydrogen and oxygen. But before the “Galileo” was crushed by atmospheric pressure, the water content of Jupiter’s atmosphere it detected was still rising. According to the infrared map of Jupiter at that time, the “Galileo” was confirmed to have fallen into a “cavity” with very little water. The average water content of Jupiter’s atmosphere is still unknown.

Recent measurements by Juno show that the atmospheric water content in Jupiter’s equatorial region is about 0.25%, which is higher than the water content previously detected by Galileo in other regions. Based on the data collected during the first eight flights of Jupiter by Juno, scientists found that the atmosphere of Jupiter’s equator was more evenly mixed. Therefore, the value (0.25%) detected by Juno can better reflect the average content of Jupiter’s atmosphere. The amount of water. The microwave radiometer onboard the Juno uses water to absorb microwave radiation of certain wavelengths, and measures atmospheric temperature from multiple depths at the same time through six antennas. The measured temperature can reflect the ratio of deep water to ammonia in Jupiter’s atmosphere, which can indirectly know the water content of Jupiter’s atmosphere.

Three methods of studying Jupiter’s atmosphere.

Weird Jupiter Lightning
In 1979, the Voyager probe observed Jupiter’s lightning for the first time. Its intensity was ten thousand times higher than that of Earth’s lightning, but its distribution was completely different from that of Earth. Lightning on the earth occurs mostly in tropical and subtropical areas where solar radiation is strong and atmospheric convection is strong, while Jupiter lightning mostly occurs at the poles. Based on the “Juneo” detection data, scientists have drawn an effect map of Jupiter’s north pole region, which shows large-scale lightning activity.

Scientists believe that the energy of lightning on the earth mainly comes from external heat, that is, solar radiation. The equatorial region receives the most radiation, where the moist warm air rises rapidly through convection, which contributes to the generation of lightning. The same principle applies to Jupiter, but Jupiter is farther from the sun than the earth, and the solar radiation received is 1/25 of that of the earth, and most of the heat in Jupiter’s atmosphere comes from Jupiter’s interior. Although the solar radiation received by Jupiter is weak, the solar radiation still makes Jupiter’s equator hotter than the poles. This makes the high-level temperature difference of Jupiter’s equator insignificant and cannot form atmospheric convection, so lightning cannot be formed. The large temperature difference between Jupiter’s poles is obvious, and the warm gas inside Jupiter can smoothly rise to form convection at the poles. Therefore, the lightning in Jupiter’s atmosphere mostly occurs at the poles.

Lightning in Jupiter’s atmosphere occurs mostly in the polar regions.

In addition, the “Juneo” recently discovered that there are smaller and shallower lightning in Jupiter’s atmosphere, accompanied by hail. This phenomenon is completely different from the lightning hail on the earth, which is produced by the Jupiter cloud layer rich in water and ammonia, while the lightning hail on the earth is produced by the water cloud. Scientists infer from previous observations that the lightning on Jupiter is formed by water clouds at a temperature close to freezing at a depth of 45 to 65 kilometers in Jupiter’s atmosphere. However, the discovery of “Juneo” indicates that Jupiter’s lightning and hail can form in a shallower atmosphere.

Scientists believe that Jupiter’s strong thunderstorm cloud throws water ice crystals into the higher atmosphere, about 25 kilometers above the water cloud, and comes into contact with ammonia. Although the atmospheric temperature at this altitude is as low as -88°C, ammonia can melt water ice. The scientist explained: “At such a height, ammonia acts like an antifreeze, lowering the melting point of water ice, forming a cloud of ammonia droplets. Falling ammonia rain will collide with rising water ice crystals and charge the cloud. Because there is no ammonia cloud on the earth, this phenomenon is surprising.”

Hail is used to explain the lack of ammonia in Jupiter’s atmosphere. Microwave radiometer monitoring of the Juno showed that most of the ammonia in Jupiter’s atmosphere was consumed. The scientist explained: “We have been trying to use ammonia rain to explain hydrogen consumption, but the depth of rain does not match the observed value. We realized that solids like hail may absorb more ammonia. After the discovery of shallow lightning, We are also aware that there is evidence that ammonia mixes with high concentrations of water in the atmosphere, so lightning is the key to solving the problem.” Scientists use “mushroom balls” to describe this kind of hail. They are just like hail on the earth at first, in strong winds. It keeps getting bigger as it pushes, until the updraft cannot support its weight, begins to fall, and evaporates in the depths of the warm atmosphere. It turns out that ammonia has not been lost, it is only mixed with water to cover itself.

The formation process of Jupiter’s hail.

The temperature of the Great Red Spot at different depths.

Depth of the Great Red Spot
The Great Red Spot-a giant storm is one of Jupiter’s most iconic features. It was first observed by humans with a telescope in 1830, but it may have existed for more than 350 years. Long-term infrared observation data show that the Great Red Spot is colder than other clouds of Jupiter, and its cloud top is 8 kilometers higher than the surrounding clouds. And one of the most basic questions about the Great Red Spot is: how deep is it? The “Juneau” microwave radiometer can peek into the deep layers of Jupiter and is an excellent “tool” for studying the Great Red Spot. Scientists explained that the “Juneo” discovered that the deepest part of the Great Red Spot can reach 350 kilometers, which is 50 to 100 times the average depth of the Earth’s oceans, and the bottom is hotter than the top. The wind is related to the difference in temperature, and the high temperature at the bottom can explain the violent storm at the top of the atmosphere.

Jupiter’s Great Red Spot

There are many debates about the future of the Great Red Spot, and observations over the years have shown that the Great Red Spot seems to be shrinking. When Voyager 1 and Voyager 2 respectively visited Jupiter in 1979, the Great Red Spot could fill up the two Earths, but today’s observations show that its width has been reduced by 1/3 and its height has been reduced by 1/ 8. People don’t know how long the Great Red Spot will last, or whether this change in size is the result of its normal fluctuations.

In addition, “Juneo” also discovered a new radiation belt above Jupiter’s equator. It contains high-energy hydrogen, oxygen and sulfide ions that move almost at the speed of light. Through the study of Jupiter’s high-energy particle detector, scientists believe that these particles originate from high-energy neutral atoms (fast-moving atoms without electric charge) produced in the surrounding gas of Jupiter’s satellites Io (Io) and Europa (Io). When the electrons of the l-generated atoms are stripped by the interaction with Jupiter’s upper atmosphere, they become ions.

Ganymede’s Arctic
On December 26, 2019, the “Juneo” flew near the north pole of Ganymede, the largest satellite of the solar system, and used the auroral infrared imager to take the first infrared image of this massive satellite’s north pole. .

Ganymede is 5,268 kilometers in diameter, which is larger than Mercury. Like many satellites in the outer solar system, Ganymede is mainly composed of ice, but it is the only satellite in the solar system with a magnetic field. Ganymede’s magnetic field is nested in Jupiter’s huge magnetosphere, and the poles are constantly bombarded by charged particles from Jupiter’s magnetosphere. Auroral infrared imagers show that the ice around Ganymede’s north pole has been changed by plasma precipitation. The ice there has not formed a crystal structure, that is, it has no fixed shape, which is clearly different from the ice in the equatorial region. Ganymede’s magnetic field introduces charged particles into the poles, violently destroying the ice structure, preventing it from forming regular crystals. The auroral infrared imager is used to detect the infrared rays emitted from the depths of Jupiter, and to detect the atmosphere 50 to 70 kilometers below Jupiter’s cloud top, but it is also used to study Jupiter’s “Galileo” satellites