A closer look at Jupiter

Jupiter, the most distant of Saturn's large moons, has always been an enigma due to the differences between one side - the bright one - and the other side - the dark one. Cassini's approach to it added to the mystery and, among other things, raised the riddle of the chain of mountains on the equator that forms a kind of great wall

On September 10.9.2007, 1300, the Cassini spacecraft made the closest pass by Jupiter. The minimum distance to the surface of the moon was 2008 km. This was the closest planned flight within the Cassini work plan. With the end of the planned activity of the Cassini in June 2012, its mission was extended by another two years and it is possible that there will be an extension for another two years, in total until the year 20. In certain segments of the spacecraft's close pass near the moon in the equatorial region, the resolution reached up to 31.12.2004 meters per pixel. This is an ability that allows a closer look at phenomena observed earlier on 123,000/1468/3.54 (a day when the minimum transit distance of the spacecraft was 80 km), but in more detail. The diameter of Jupiter is 80 km, the distance of its orbit from Saturn is XNUMX million km "m and circles it once every XNUMX days. Jupiter is the most distant of Saturn's large moons. Since it only shows one side of Saturn, its day is particularly long - XNUMX days.

The relief in the equatorial region

One of the prominent phenomena that Cassini detected on Jupiter during its first pass is a ridge line at the equator. The measurements showed that the ridge line is 1300 km long, 13 km high and 20 km wide. Craters were found on the slopes of the relief and on its summit. In the near transit flight it was found that in some places the height of the relief is 20 km. The relief is not continuous and its appearance is fragmented (photos.jpg5201W000, W00035149.jpg). In an attempt to find an explanation for the question of the formation of the relief, they associate this phenomenon with the slow rotation of the moon around Saturn (18.7.07web: "Saturn moon"). According to a model that the researchers built, Jupiter will circle around itself once every 5 hours and circle Saturn once every 16 hours. A phenomenon somewhat reminiscent of the movement of Mercury around the sun. This planet revolves around itself once in 55 days and orbits the sun once in 88 days. Each of its 3 revolutions around itself is equal to 2 revolutions around the sun. This rapid rotation gave Liptos a flattened configuration that increased the surface area. Over time the axial rotation rate slowed to 16 hours and the outer shell of the moon froze. Moreover. The surface of the cold moon shrank and the excess material became too rigid to return inward into the lunar body. Instead it piled up into a mountain chain at the equator. In order for tidal waves to slow Jupiter to its current rate of axial rotation, the interior of the moon must be hotter near the melting point of water. ice.

The life span of the heat source must be limited in time to allow the lunar crust to cool quickly and obtain a "mature" configuration. According to various estimates, the heat source comes from rocks that contain short-lived radioactive isotopes - aluminum 26 and iron 60 - which decay rapidly in geological time terms. Since these isotopes decay at a known rate, it is possible to date Jupiter similarly to the dating done using carbon 14. A calculation based on aluminum 26 showed that the age of Jupiter is 4.5 billion years. Such isotopes were found in various meteorites in the inner part of the solar system.

The problem with this model is the distance of Jupiter from Saturn. A distance of 3.5 million km. If we take another moon of Saturn, see it has a similar size, its diameter is 1530 km (slightly larger), it orbits Saturn once every 4.5 days and its orbital distance from Saturn is 524,000 km. When checking the ratio of the distances of the planets from the Sun and the ratio of the lunar distances of the planets, in each group this ratio usually converges to a value smaller than the number 2 (Mazar 34:2002). Jupiter exceeds the value 2 by several orders of magnitude. This calls for two possibilities. According to one possibility, Jupiter used to be closer to Saturn. It is possible that it really circled it once every 16 hours and for whatever reason was thrown into a more distant orbit, perhaps due to a collision with another body. The second possibility is that Shiftos came from another place in the solar system. Perhaps it orbited another planet, was thrown out of its orbit and began to move through the solar system until it was captured by Saturn's gravity. And again the question of the origin of the relief returns.

The differences in darkness between the two sides of the moon

The most striking phenomenon that has been observed on this moon since telescopes were aimed at it is that one side is very bright and the other side is very dark. The dark part of the moon faces Saturn and the bright side is not exposed to the planet. The shape of the dark area is elliptical. One end is at longitude º330 and the other end is at the 240° longitude. The coverage range is 270º. The northern demarcation is between latitudes N°60-N°55 and the southern demarcation is at S°55. The name of the region is Cassini Regio. During the passage that the Xassini carried out in 2007, it became clear that the area is littered with craters. 3 large craters are well distinguished, one with a diameter of 424 km, this is the Falsairon crater, the other with a diameter of 580 km and its name is Turgis. This crater is in the lower eastern part and it borders the relief of the equator. Another large crater named Malprimis with a diameter of 377 km is between the longitudes 150° - 95°. The color darkness in this area is not uniform. The texture of the surface shows shades. The map prepared following the photographs of Jupiter (PIA08406 web) sharpens the question that has accompanied the researchers for years regarding the origin of the darkness. Is it the result of geological processes that resulted in material being ejected or is it material that came to Jupiter from other moons and if so from which ones?

The bright areas of Jupiter are in the high latitudes and in the space between the ends of
Cassini Regio. In the southern part of the moon between the longitudes °280 - °240 there is a crater with a diameter of 504 km and flat and its name is Engelier. As you move from the bright areas to the dark area, the brightness gradually weakens until it becomes dark. At longitude 330° at the eastern end of Cassini Regio, there is a crater with a diameter of 244 km and its name is Naimon, which is dark at the bottom and has a round and bright spot in the center. A crater with a "color reversal" is located near the North Pole. Its bottom is dark, the strongest darkness on the moon and around it are two bright surfaces whose brightness is the strongest on the surface of the moon. To the east of them are two craters, one inside the other, covered with light material, except for part of the inner wall of the inner crater, and to the east of them, another crater can be seen, the bottom of which is a transitional color between the light of the environment and grayish (PIA08206web). The entire Jephtus is covered with craters. The number of craters with a diameter greater than 200 km is 8.

water and CO2

The prevailing trend regarding the origin of Jupiter's dark color is that it was "imported" from other moons whose direction of movement around Saturn is opposite to its own. As soon as the side facing Saturn becomes very dark, a rapid heat separation of the surface occurs. A dark area absorbs more of the surface heat and begins to heat up, so that the water ice begins to evaporate. The vapor condenses in the cold area and on the nearest side which can be at the poles and low latitudes on the hidden side from Saturn. The dark matter loses water ice and becomes darker and the light matter accumulates ice and becomes even brighter in a process called the Runaway Process.. Since the number of small craters on Jupiter digging into the light ice layer is small, it is estimated that the dark matter layer is thin, if Because there are places where this layer is thicker. It seems that the dark material lies on the top of the light areas. A fact that supports this approach is a residual material produced by the sublimation of water ice ("Cassini is" 8.12.07web).

The findings show that the area becomes cleaner of water ice with the movement north or south of the equator and the area of ​​the area facing Saturn on the other side. The movement of the ice increases the concentration of dark matter in these areas. One of the surprising results of this is the increase in the concentration of CO2 since the gas is more volatile than water. The obvious conclusion is that the gas is trapped in the ground and its presence in the equatorial region is stable (PIA10010:web).

Temperatures

Due to the long day of Jupiter, various places in the area of ​​the equator can accumulate heat during the day and cool down to an unusual degree at night. The dark areas of Jupiter can absorb a large amount of sunlight and be heated by it to a greater extent during the day than the bright areas. In most of Saturn's moons the temperature difference between noon and midnight is 20°C, while on Jupiter it is much greater. The temperature range is between
C°-165 at noon to C°235- at midnight.

In the section between W °212 N °36 and W °220 S °22 located in the section between the eastern end of Cassini Regio and its western end, it was found that the temperature differences at the equator are between -145 °C in the bright areas and -160 °C in the bright areas ( PIA10012: web ).

This small temperature difference has a big effect on Jupiter. Because at the temperatures of the dark zone a large amount of water ice that is very common on most of the surface of Saturn's moons can be lost due to evaporation over millions of years. The temperature during the day reaches C ° 145 - a layer of 20 meters of water ice is lost over millions of years. In the bright areas where the temperature is 160 ° C - a layer of 10 meters of water ice evaporates in the same period of time. It seems that with the complete evaporation of the ice from the face of Jupiter, the dark surface of the moon becomes darker and the bright areas adjacent to them become brighter and as a result increase light changes. This process is defined as thermal segregation. According to various models, water that evaporates in the dark zone can accumulate at high latitudes and thus explain the brightness of the poles on the dark side of the moon facing Saturn. In the same way, it is also possible to explain the relatively dark zone at the equator on the hidden side of the moon (PIA10012: web).

discussion

The wide spread of the dark zone makes it a geological phenomenon of global proportions. This is an area littered with craters including 3 craters on the order of hundreds of kilometers with craters inside them as well. The darkness of the surface is not uniform. It fades away in the border area in the north and south towards the poles, which further sharpens the question as to its origin, external or internal. Does it come from other moons or as a result of geological processes? The bottom of the Turgis crater is darker than the other areas of the Cassini Regio. Near the southeast inner wall is a crater with a diameter of 121 km and its name is Malun. What characterizes this crater is the discovery of rockslides on the western slopes of the inner wall, similar to the phenomenon of mountain landslides on Earth. The bottom of the Turgis crater is more or less flat, which means that the surface of the crater floor was filled with material that erupted out of the lunar crust and leveled it And then came another crushing. A similar process took place in the Malun Crater and then came the rockslide. The floor of the Malun Crater is also dark but it is a little lighter than the bottom of the crater in which it is located. These data make it possible to make a stratigraphic section of the Turgis Crater as a whole and to determine its relative age.

The bottom of the other two large craters in Cassini Regio, Falsaron and Malprimis, is similar in its degree of darkness to that of the region as a whole. If you look at Cassini Regio as a whole, you get the impression that it is the product of the formation of two giant craters of a global scale that shook the entire moon and at a later period the craters were formed which we referred to earlier. They were followed later by bursts of lava from the lunar crust, similar to similar phenomena on other planets in the solar system and their moons. On other moons, the large craters are hundreds of kilometers apart from each other. On Jupiter, the sides of these craters touch each other to the point of creating a chain of earthquakes that led to an eruption Lava that destroyed and covered their touching sides. It is possible that the relief on the equator is a later product of these impacts. It is also possible that the rockslides in the crater are related to this. A possible support for this hypothesis is if they find in Cassini Regio masses (concentrations of mass) like on the Earth's moon.

The proposed model according to which the strong darkness of the side facing Saturn leads to its warming over geological timescales and consequently to the evaporation of the water ice in the process of sublimation and its accumulation in other places is problematic. Jupiter is too small to have an atmosphere in all its meteorological meanings, what's more, during sublimation a large part of the water vapor escapes quickly. Another question that arises from this model is what is the quantitative ratio between the water vapor that escapes from the moon and that which refreezes. We must therefore think about the possibility Other. If we examine the Engelier crater, it appears that in its east are the remains of an earlier crater which it cut. Both are covered with a light material that is also found around them and covers large areas. From the point of view of the stratigraphic section, this covering layer was formed after the formation of the Engelier crater. The light material appears in different places in the form of spots. There are Places where it is found inside craters (photo. N00093117.jpg) and in other places it covers plains and slides into craters (photo PIA08375 web). An alternative explanation for the sublimative process is the existence of underground water sources, perhaps water aquifers or underground oceans of Water similar to Europa, a moon of Jupiter. In various places, this water erupted and perhaps erupts even today, not in the form of geysers like on Enceladus, but in weaker intensities and froze quickly. This is how the layers of ice are piled on top of each other. The size of the light areas can indicate the duration of the process of the water breaking out.

A similar but opposite phenomenon is that of bright areas covered with dark spots (photos PIA08374:web, PIA08373:web). There may indeed be a situation in which many dark spots will be found in different areas but without any continuity. The spots are isolated. They too can be the product of material breaking out of the lunar crust as small Hot Spots.

The comparison of the temperatures measured by the Cassini during its transits in 2004 and 2007 allows the beginning of the construction of thermal profiles in hot spots on the surface of the moon while taking into account the lightness and darkness of the ground. This comparison will allow mineralogical mapping and the precise locating of thermal sources within its crust where the phenomena of the moon were found - Hot Spots. If this is indeed the case, the obvious question is, are there convection currents inside the moon?

Summary

The totality of all the phenomena found on Jupiter makes it similar to Enceladus (although on the moon for other reasons) a unique phenomenon not only within the space of Saturn, but also in the entire solar system. For future missions to Saturn, it is worth thinking about a spacecraft that will enter orbit around it, including two all-terrain vehicles that will move One in the dark area and one in the light area.