Geysers and water on the moon Enceladus

Cassini's close passes to the ground allowed it to directly sample the water in the geysers. This type of test is considered the best proof of the existence of large, salty water reservoirs under the crust of Enceladus

The geysers

In order to obtain a panoramic view of Enceladus on 21.11.2009 a series of high resolution photographs of the moon was taken. The result is a spectacular mosaic image showing eruptions of geysers. 30 geysers of different sizes were identified in the mosaic image. 20 of them were not seen in previous observations. One of the geysers was seen in previous photographs, the intensity of its eruption was weaker compared to previous eruptions (1). During one of Cassini's transit flights near Enceladus, the spacecraft moved inside one of the geyser plumes and tested the molecular weight of the water with the aim of identifying chemical components attached to the ice emitted during the eruptions of the geysers, and sodium salts and sodium bicarbonate (3 NaCO) were identified. The origin of these compounds is from the lunar body itself. They moved from the nucleus through liquid water (2). In other observations, organic molecules were also identified (3). Due to the very short distance of the spacecraft from the lunar surface (tens of kilometers and in one case the distance was no more than 25 km) these observations can be considered as if they were conducted under laboratory conditions.

This quasi-laboratory test is equivalent to a test under real conditions in relation to the abnormal behavior of plasma. The findings of the Cassini confirmed the hypothesis according to which there is "dusty plasma" near Enceladus. The moon is essentially a large reservoir of ionized material that fills a magnetic bubble moving around Saturn. The rate of water vapor emission from the moon is 100 km of water per second, similar to that found in active comets. The total material ejected from the moon is a mixture of ice grains plus neutral gases. The geyser plume becomes charged particles that interact with the plasma surrounding Saturn.

The size of the emitted grains ranges from several molecules up to 100 micrometers. A large part of these grains, on their way out, capture electrons from the ground. It turned out that in this environment of Enceladus positively charged ions are the "light" plasma and the negatively charged ions are the "heavy" plasma. At least half of the negatively charged electrons are attached to the dust and their interaction with the positively charged particles slows down the movement speed of the ions. Since dust has an electrical charge and behaves like a part of the plasma, there are researchers who make a distinction between it and dust that happens to be inside the plasma. For this reason, a distinction is made between "powdery plasma" and "dust present in the plasma". This last situation is typical in interplanetary space. The conditions in the "dusty plasma" allow the dust to be part of the behavior of the entire plasma. For this reason, the complexity that changes the properties of the plasma increases and creates a new collective action pattern (4).

Cassini's close passes to the ground allowed it to directly sample the water in the geysers. This type of test is considered the best proof of the existence of large, salty water reservoirs under the crust of Enceladus. According to these findings, the researchers came to the conclusion that the water layer is found at a depth of 80 km below the ground, between the rocky core and the ice shell. The water is in a liquid phase due to the tidal forces of Saturn and nearby moons and also from heat generated by radioactive decay. The water reservoirs must have large evaporation areas, otherwise they freeze and prevent the plumes from forming. It is important to note that in terms of the moon's astronomical position, there should be no water in it. Its distance from the sun is too great for this purpose (5).

In June 2011 the Herschel Space Telescope found a torus-like cloud of water vapor coming from this moon orbiting Saturn. This cloud is 600,000 km long and 60,000 km thick and is probably the source of the presence of water in Saturn's upper atmosphere. In previous telescopic observations it was impossible to distinguish this ring because water vapor is transparent for most wavelengths in the visible range. The discovery was made using the infrared detector of the telescope (6).

Measuring the color characterization of the surface shows that the ice particles return to the ground according to a repeating pattern. It turned out that the phenomenon of the plumes and their heat sources have a long lifespan and their age is thousands of years and possibly even tens of millions of years and that in the past large parts of the surface were covered with a thin layer of ice particles (7).

Tidal forces

From the set of photographs taken until the beginning of 2012 it is possible to see for the first time that there is a correlation between the jets of water vapor and Saturn's gravity. This finding allows researchers to develop new insights into the mechanism of these jets, indicating that Saturn creates pressures on Enceladus. It turned out that these pressures push the lips of the tiger stripes apart from each other, when Enceladus during its movement around Saturn is just before the transition at the closest point to the planet, Saturn's gravity begins to distort these cracks. Tidal forces mean that a large reservoir of water on a global or local scale results in Enceladus being flexible (flex to) to produce large pressures that distort the surface. It is this process that schedules the eruptions of the water jets. It has also been hypothesized that Saturn's tides create a lot of heat on the surface (8).

The deformation in its shape as gravitational tidal forcing creates pressures that crack the ice in several places and probably changes them on a daily basis. The tidal forces can open and close the crack openings and cause the crack lips to move several centimeters apart. This force also creates friction which releases additional heat to the surface.

It also turned out that the power of the tides is not enough to create the full heat emitted to the surface. It has been hypothesized that some of the heat today was created and stored in the moon in the past. According to this hypothesis, Enceladus' trajectory was previously more eccentric. The greater the eccentricity, the greater the power of the tides and causes structural changes in the moon, which create the heat. In this case the heat is stored inside the moon by melting some of the ice. and adds it to the liquid water. With the reduction of the eccentricity, the heat is released to the surface and today it is a combination of the heat generated today and the heat stored in the past, since more heat is released than was created. The moon is in the phase of cooling and the water turns into ice again. According to other models, the moon does not freeze completely and that the eccentricity can increase again and a new cycle of heating opens (10).

surface temperature

On the transit flight carried out on August 11.8.2008, 103, a temperature of 100°C was measured - in Damoscus Sulcus, a temperature 11° higher than that in the immediate vicinity. It may be that in some places the temperature is even higher (10.2009). In the measurement made on 165, 93-C ° was measured in different sections in Sulcus Baghdad, the temperature measured was higher than 12-C ° (2012). In the measurements made in 83, a temperature of 10°C was measured in some of the cracks (XNUMX).

Sources

1. PIA11688: Bursting at the seams
http://photojournal.jpl.nasa.gov/catalog/ PIA11688

2. "Salt in ice plumes hint at liquid on Saturn's moon" 1.5.2009
http://timesofindia-indiatimes.com/articleshow/msid-4469861s/prtpage-1.cms

3. "Cassini tastes icy material from Saturn moon geyser" 4.11.2009
http://www.spaceflightnow.com/news/n0911/04enceledus/

4. "Enceladus plume is a new kind of plasma laboratory" 1.6.2012
http://www.spacedaily.com/reports/ Enceladus_ Plume_ Is _A_ New_ Kind _Of_ Plasma _Laboratory_999.html

5. "Cassini samples the icy spray of Enceladus water plumes" 24.6.2011
http://www.spacedaily.com/reports/ Cassini _Samples_ The_Icy _Spray _Of_ Enceladus _Water_ Plumes_999.html

6. "Saturn moon Enceladus spreads its influence" 23.9.2011
http://www.spacedaily.com/reports/ Saturn_ Moon _Enceladus _Spreads_ Its_ Influence
_999.html

7. "Enceldus weather includes snow flurries" 5.10.2011
http://www.spacedaily.com/reports/ Enceldus_ Weather_ Includes _Snow_flurries_999.html

8. "Cassini sees Saturn streaming out Enceladus" 21.3.2012
http://www.spacedaily.com/reports/ Cassini_ Sees_ Saturn_ Streaming _Out_ Enceladus
_999.html

9. "Saturn's icy moon may keep oceans liquid with wobble" 7.10.2011
http://www.spacedaily.com/reports/ Saturn’s_Icy_ Moon_ May_ keep _Oceans_ Liquid _With _Wobble_999.html

10. "Is it snowing on Enceladus?" 29.3.2012
http://www.spacedaily.com/reports/ Is_ It _Snowing_ On_ Enceladus_999.html

11. PIA12082: Warm Tiger Stripes
http://photojournal.jpl.nasa.gov/catalog/ PIA12082

12. PIA12448: Zooming in on heat at Bughdad Sulcus
http://photojournal.jpl.nasa.gov/catalog/ PIA12448