Enceladus - new findings. Part a'

Among Saturn's moons, after Titan Enceladus has become the most geologically intriguing moon. The more photographs arrived, the more and more the interest in him grew

introduction

Among Saturn's moons, after Titan Enceladus has become the most geologically intriguing moon. The more photographs arrived, the more and more the interest in him grew. The surface was slowly and fully revealed until a complete global image was obtained. With the end of the original Cassini program, a new action plan was built and one of the decisions was to make several more transit flights near this moon. In one of these flights they dared to approach 25 km from the surface of the ground and the geology turned out to be particularly rich. The high resolutions of the photographs reached the order of a few meters per pixel.

atmosphere

The biggest surprise was atmospheric presence. Since this is a very small body, 500 km in diameter, it is clear that this is not a gaseous envelope that surrounds the moon. What was observed were geysers of water at the South Pole. These geysers emit large amounts of water vapor and these create an atmosphere-like phenomenon for a short time. It is actually a local and short-lived atmosphere. Confirmation for this assumption was given in the tests done with the help of stars that "passed" near the moon. These are two stars. The first is Bellartrix, when it passed near Enceladus on July 11.7.2005, 1. From the point of view of the spacecraft, its light dimmed near it to the moon. When it was discovered on the other side of the moon, there was no dimming of the light coming from it. The other star is Lambda Scorpius which passed by the moon in February of that year and its light did not dim at all (2). It also turned out that the atmosphere changes between one transit flight and another. It is estimated that the origin of these changes is at different levels in the activity of the geysers in the South Pole that cause these atmospheric changes (XNUMX).

The main component of the material emitted from these geysers is water which is divided into two types. Pure water ice coming from the surface and water ice mixed with other materials coming from inside the moon. These are very small particles on the order of 1/10 of an inch that burst out at a speed of 000 km/h and reach a distance of 1280 km from the face of the moon. Other components that are emitted in small quantities are CO and CO1500. Ammonia, methane and ethylene (2, 3).

The particles, the ice grains and the water vapor that break out are too small to create any kind of interaction between themselves, they cannot reach the ground quickly. The descent is slow. It is estimated that the change in speed occurs underground before they are ejected. The depth of the fissures through which the geysers erupt is hundreds of meters and in some places the temperature and pressure of the water drops drop and cause their condensation into ice grains and the creation of the mixture of water vapor and dust. The density required to accelerate the grains to speed Which can be observed, requires liquid water temperatures that can coexist with water ice and water vapor within the frozen crust of the moon. These conditions allow the water vapor and the dust particles to break out together. These particles undergo many collisions among themselves and between them and the sides of the cracks, which causes friction and a slowing of speed before they break out. The larger the particles, the lower the speed of their ejection (5).

Most of the particles return to the ground, but the smallest particles escape from the moon. As a result of the radiation pressure (light) and the interaction with Saturn's magnetosphere, they form the E ring, a ring that is constantly renewed due to supplies reaching it through geological processes occurring below the surface of Enceladus (6). To the surprise of the researchers, it turned out that some of the emitted particles also reach the outer rim of ring A. The plasma that creates the tar-like cloud around Saturn is "kidnapped" by this ring like a sponge that absorbs the plasma (7).

The heat generated inside the moon is high enough to allow the water ice to immediately pass into a gaseous phase as in comets when they approach the sun. It is estimated that the source of heat inside Enceladus is related to tidal forces. The two occurrences are similar and allow the location of the openings through which the gases are emitted both in Enceladus and in comets (8).

The geysers and their origin

Geographically, the geysers erupt from 3 large canyons called "Tiger Strips". It is clear that the source of the geysers is hot water, probably of an oceanic size. The obvious question is what heats the water. It is estimated that the orbit of the moon around Saturn plays an important role in heating the water. The Moon's orbit is eccentric, sometimes it approaches Saturn and sometimes it moves away from it, and Saturn's gravity changes over time, although this is done cyclically. Tidal forces are created that cause the "tiger stripes" to move back and forth. According to this model, the water does not have to be close to the surface, but deeper. An ocean that is under the ice crust. This location allows the ice crust to deform with a force that allows movement along the canyons. If the ice is just above the rocky upper edge of the moon, the tidal forces have not created enough motion in the canyons to create heat. This frictional mechanics is consistent with previous research that the moon orients itself to position the hot spots at the south pole. According to the estimate, the thickness of the ice layer is 5 km and can reach tens of kilometers and the movement along the canyons is at a rate of 0.5 meters during the orbit of Enceladus on Saturn, the length of a tidal cycle. The friction causes the wave forces to move along the crack lines back and forth and rub against each other. In this way they create a lot of heat which causes some of the ice to immediately turn into water vapor and ice crystals. The underground ice heats up near the active fissures, close to where the gases erupt (9).

This approach turned out to be problematic when an observation towards the moon in 2007 showed that the amount of vapor emitted from the canyons was greater than expected at the time when the tidal forces were supposed to operate. Although the frictional approach was not completely ruled out, another possibility was raised to solve the problem. Water from a liquid reservoir on the surface of the moon. Using the flickering light of a star and which the geysers block it, it became clear that the water vapor creates a narrow jet. The possibility was raised that only a temperature close to the melting point of water ice can support the high speeds of the water vapor jets (10).

An important and noteworthy point is that in many cases where the geysers were examined while they were hiding a star that "passed" through an eclipse technique, 4 gas jets were found each with a different density of water vapor. The density of water vapor is twice as high as the gas envelope surrounding each gas jet (2 ).

Makhteshim

The mapping of Enceladus showed a significant difference between the Northern Hemisphere and the Southern Hemisphere in terms of crater density. The area near the North Pole is geologically the oldest and has the highest density of craters. In the Northern Hemisphere there is a very wide and narrow area starting at the equator starting on the side facing Saturn, reaching the pole and extending to the equator on the other side of the moon. The area near the equator and mid-latitudes between longitude W ° 90 (on the side facing Saturn) and longitude W ° 270 (on the side hidden from Saturn) is less dense in craters and the surface is characterized by cracked and broken areas.

In the Southern Hemisphere, a cratered area between longitudes °180 - °0 extends south from the equator, but from latitude S °55 to the pole, instead of craters, a system of cracks and fractures is found around the pole. At the pole itself, there are almost no craters (12).

The craters in the Northern Hemisphere are in different stages of fracture and it is evident that there was tectonic activity in them and they probably went through a phase of heating from below. Many of the craters are cut by small, parallel cracks. It is possible to distinguish different shapes of craters. In some of them you find spherical reliefs and inside these are smaller craters, which implies that the ice crust in this area was warmer in the past (13). The craters are small. The largest crater, the Ali Baba crater, has a diameter of 39.2 km.

cracks and fractures

The photographs show that many parts of the surface of Enceladus are sloped with cracks and fractures, which indicates a rich tectonic history of the moon. A morphologically similar phenomenon is found in Jupiter's moon Ganymede. This geological activity can be used as a good clue as to the many changes that have occurred on the surface of the moon. An extensive field for stratigraphic studies. Most likely these cracks were created due to tidal forces activated by Saturn and/or changes in the internal structure of the moon. A prominent phenomenon found in the South Pole is 3 canyons, these are the "tiger strips" we mentioned earlier. They are about 128 km long, 1-2 km wide and 40 km apart. Wide networks of folds separate the "young" surface of the South Pole from the ancient surface near the equator surrounding the Moon near latitude S ° 55. The boundary line of the South Pole is cut by cracks in funnel-like formations, discontinuities that curve northward They are explained by the fact that they were created by tensile pressures parallel to latitude lines. Cracking patterns are found both in ancient and crushed areas and in young areas. There are also crack systems in the Northern Hemisphere and their directions are north-south and east-west that were created near the tidal axis. The tidal axis is a line that extends from longitude ° 0 to longitude ° 180. It is possible that they were created as a response to tidal pressures by Saturn (14, 15). The close passes of the Cassini up to a distance of 25 km from the surface in October 2008 allowed for the first time a detailed look into the sides of the canyons and in some places at their bottom.

The ground surface in high resolutions

Thanks to the exposure of the soil in high resolutions, it is possible to observe and examine details on the order of a few meters, which enables studies regarding the composition and structure of the soil in very small areas from a topographical and morphological point of view. In photograph 06252 PIA, which was taken with a resolution of 4 meters per pixel, ground formations of polygons were found, reminiscent of the photographs transmitted to Earth by the Phoenix spacecraft which landed near the north pole of Mars, and ice blocks were observed in the order of 10-100 meters. Their origin is unclear (16). In photograph 10350PIA, with a resolution of 5 meters per pixel from the South Pole, soft material can be discerned in several valleys between the rounded hills. The height of the relief at the site is 250 meters. Formations of small buttons were found that are 10-50 meters wide and 2-10 meters high (17). Blocks of ice were found near the Cairo Sulcus area (18). It turned out that the depth of the "tiger strips" reaches up to 300 meters and their inner walls have a V-shape. In some parts of these canyons one can notice extensive deposits of fine material and around the canyons blocks of ice tens of meters long. Along several cracks you can see that there was a fall of ice particles to the ground. They are also found between two sources of geysers. It is estimated that since hot water vapor rises up through narrow cracks, the ice particles condense and block active exit openings, new geysers will appear in other places along the same crack. For the first time, the researchers are given the opportunity to understand to what extent the sediments of fresh eruptions covering the ground differ from sediments of previous eruptions. Throughout geological periods, the location of these eruptions moves up and down along the length of the "tiger strips" (19). In photograph 1112PIA, areas are seen that are probably covered with rough ice grains and rock blocks that are difficult to distinguish at the resolution of this photograph. This photograph is a mosaic of photographs with resolutions different and it can be seen that the coarse grain ice and solid ice are concentrated along the bottom of the cracks and the sides as well as along the raised parts of the "tiger strips" elsewhere on Enceladus these ice grains are found in sections protruding from rocks and on the tops of ridges (20).

Sources

1.PIA03552: Enceladus atmosphere not global

http://photojournal.jpl.nasa.gov/catalog/PIA03552

2. "Saturn moon is source of solar system largest planetary ring" 13.3.2006

http://www.saturndaily.com/reports/ Saturn_ Moon_ Is _Source _Of_ System_ Largest_ Planetary_ Ring_.html

3."Cassini space spacecraft to dive into water plume of Saturn Moon" 11.3.2008

http://www.saturndaily.com/reports/ Cassini_Space_Spacecraft_To_Dive_Water_Plume_Of_Saturn_Moon_999.html

4. Stiles L. - "Tiny Enceladus may hold ingredients of life" 6.9.2005

http://www.spacedaily.com/news/cassini-05zzzf.html

5. "New theory sheds light on space enigma" 25.2.2008

http://www.saturndaily.com/reports/ New_ Theory_ Sheds_ Light _On_ Space _Enigma_999.html

6. "Multiple Cassini instruments capture Enceladus plume" 17.12.2005

http://www.spacedaily.com/news/cassini-05zzzze.html

7. "The giant sponge of Saturn" 6.2.2008

http://www.saturndaily.com/reports/ The_ Giant_ Sponge_ Of _ Saturn_999.html

8."Cassini findings suggest complex story of venting at Enceladus' south pole" 31.8.2005 http://www.spacedaily.com/news/cassini-05zzy.html

9."Frictional heating explains plumes on Enceladus" 17.5.2007

http://www.saturndaily.com/reports/ Frictional _Heating_ Explains_ Plumes_ On_ Enceladus_999.html

10. "Source of geysers on Saturn's moon may be underground water" 27.11.2008

http://www.saturndaily.com/reports/ Source_ Of_ Geysers_ On_ Saturn_ Moon_ May_ Be_ Underground_ Water_999.html

11.PIA10354: Stellar data on plume

http://photojournal.jpl.nasa, gov/catalog/PIA10354

12.PIA07220: Enceladus: north and south (southern polar projection)

http://photojournal.jpl.nasa, gov/catalog/PIA07220

13.PIA08409: The north polar region of Enceladus

http://photojournal.jpl.nasa, gov/catalog/PIA08409

14.PIA07722: Enceladus global patterns of fracture (southern polar projection)

http://photojournal.jpl.nasa.gov/catalog/PIA07722

15."Cassini finds Enceladus Tiger Stripes are really cub" 31.3.2005

http://www.spacedaily.com/news/cassini-05zzz.html

16.PIA06252: Boulder-strewn surface- narrow angle camera view

http://photojournal.jpl.nasa.gov/catalog/PIA06252

17.PIA11350: South polar terrains of Enceladus – highest resolution view

http://photojournal.jpl.nasa.gov/catalog/PIA11350

18."Cassini returns pictures from Monday's fly by of Enceladus 12.8.2008

http://www.spaceflightnow.com/news/n0808/12cassini/

19. "Tracing tiger stripes" 28.8.2008

http://www.saturndaily.com/reports/ Tracing_ Tiger _Stripes_999.html

20.PIA11112: Great southern land

http://photojournal.jpl.nasa.gov/catalog/PIA11112