Comprehensive coverage

Callisto-Moon of Jupiter

Callisto's density is very small. It makes up 33% of Mercury's density. This basic figure can give a preliminary indication of its internal composition. In terms of photographic coverage, it was photographed by the two Voyager spacecraft, the Galileo spacecraft, and New Horizons, which transmitted several photographs of it to Israel on its way to Pluto.

Callisto. Photo: NASA
Callisto. Photo: NASA

Callisto, the most distant of the Galilean moons, has a diameter of 4840 km and is the same size as the planet Mercury, 4878 km. The density of the latter is 5.44 g/cm1.8 compared to Callisto's density of 60 g/cm33. Mercury is the body with the highest density among the bodies surrounding the Sun and its nucleus is very large. Its core mass is XNUMX% of the mass of the planet and occupies a large part of its volume. Callisto's density is very small. It makes up XNUMX% of Mercury's density. This basic figure can give a preliminary indication of its internal composition. The first impression received is that the size of the core is hundreds of kilometers and that it has large aquifers of water and has a large content of low-density minerals. Therefore, some of the rocks also have a low density. In terms of photographic coverage, it was photographed by the two Voyager spacecraft, the Galileo spacecraft, and New Horizons, which transmitted several photographs of it to Israel on its way to Pluto.


Callisto has a thin atmosphere of CO2. The atmospheric pressure is -1210X7.5 bar and the temperature near the ground is -123°C. In terms of density, it is actually an exosphere like Mercury's atmosphere, although it has a different chemical composition and the temperature differences are very large. Several possibilities have been put forward to explain this atmosphere. According to one explanation, gas burst out of the interior of the moon and evidence of sublimation of the surface was indeed found. A large release of gas during the stages of formation of substances containing it or by the passage of aqueous substances of primitive carbonaceous compounds. According to both explanations, the atmosphere and the CO2 from the ground mix on the surface and not from an internal source. Interaction between ultraviolet radiation and charged particles can create and release CO2 from internal materials or carbon-containing materials present on the surface. Chemical production of CO2 and other volatiles can occur following collisions of large bodies with the lunar soil and following the bombardment of micrometeorites. Another source could be the continuous growth of CO2 from cometary matter (1).


According to the photographs that were broadcast to Israel, it appears that Callisto lacks geological characteristics known on the surface of the Earth and other bodies in the solar system such as canyons, volcanoes, channels, etc. It is possible that there was geological activity on it in the past, but the evidence for this is not clear. The geological changes that left their mark on it are craters and they make up 70% of its surface (2). Most of the craters are less than 100 km in diameter. The distribution of the craters of craters with a diameter greater than 100 km is as follows - 32 craters with a diameter of 100-200 km, 3 craters with a diameter of 200-300 km, 2 craters with a diameter of 300-400 km, 1 crater with a diameter of 410 km, 1 crater with a diameter of 660 km, 1 crater with a diameter of 980 km (3).

Close-up photographs taken when the Galileo spacecraft passed at a distance of 138 km from it and craters with a diameter of 3 meters were recorded, although their number is less than they thought. Indented hills were found near one of the craters. They look like ice thrown out of the ground as a result of the impact of a large body that hit the surface (4). Many of the craters are bright. The source of this brightness is the material that was excavated in the lunar soil when the craters were formed, a material that contains large amounts of water. The end result is powdery material that covers large parts of the surface (5). Some of the young craters are 40% as deep as the craters of the Earth's moon (2), which indicates a low topography. Callisto's relief height is similar to that of Mercury.

Many of the craters have depressions in their center. Probably a reaction of ice to the process creating the injury. The bottom structure of young craters changes with their larger diameter. Small craters are deep and their shape is concave. Large craters are shallow and their bottom is relatively flat. Ancient craters, their bottom is almost at the same height as their surroundings. Despite the heavy bombardment of bodies that created the craters, the languages ​​of many of them were preserved (7).

The largest of the craters is the Valhalla crater. It is a multi-ring crater, in the center of which is a bright area with a diameter of 600 km and it is surrounded by concentric rings with a diameter of 3,000-4,000 km. The bright material in the center was probably created due to digging and throwing "cleaner" ice that was under the ground and "Impact Melts" filled the crater after its formation. The concentric rings are cracks created due to the impact (2,8).

The second large crater that also has concentric rings is the Asgard crater with a diameter of 370 km. The concentric rings reach up to a distance of 1900 km from its center. In the center are also bright areas and lumps of ice and what caused their formation is unclear (9) as in the Valhalla crater the rings were formed following an impact that created it they were formed by a tectonic process. You can see craters on the rings, which means they were created later. In the northern part of the Asgard basin is the Burr crater with a diameter of 71 km and from it emerge rays that cover the northern and outer segment of the concentric rings (10). This concentricity of the rings is also found in the Chloris Basin on Mercury.

Two unique craters are the Doh crater which is 55 km in diameter and has a domed relief in the center (11) and the Har crater which is 50 km in diameter and also has a domed relief in the center (12). This is not a shock wave following the formation of craters that creates a bulge in their center. It seems to be a completely different process. These formations resemble bubbles formed in boiling water. It is possible that convection currents developed in these places long after the formation of the craters. These currents raised the floor of the crater. It is likely that there was a gas leak in these places and the density in them is lower than the global density of the moon. They are probably made of materials rich in water ice. A question that can be asked is why with the cooling, these formations did not sink? One possibility is that these processes took place not long ago (in geological terms, perhaps thousands or tens of thousands of years). A second possibility is that the convection currents are still active and occasionally push additional gases from below and strengthen the configuration so that it does not collapse.

Rockfalls can be seen in several photographs. These are rocks that broke away from the sides of craters and deteriorated to their floor (13,14,15). An explanation put forward for this phenomenon is meteorites that hit the environment of these craters, creating seismic activity that resulted in the detachment of the rocks and their deterioration. The result, the exposure of internal parts of the rock and most likely they were also exposed to the sun's radiation and it acted on them. In future flights to Callisto, spacecraft will be equipped with cameras with greater resolutions and it will be possible to examine these craters in more detail. The inspection of these will be more thorough if spaceships are landed in these places.


These are arrays of concentric fragments that appear as topographic remnants around circular shapes with high light reflectance indicating that they were originally deformed impact craters and are probably very ancient. Craters with a "black halo" are explained as craters that dug into the light material and they indicate that the light material that forms the Palimpsets is at most 1 km thick. At least 11 palimpsests have been identified on Callisto. They have almost no topographic prominence and are difficult to map accurately. Younger palimpsets within the multi-ring basins such as Valhalla and Asgard are easier to identify. Their shape is between elliptical and circular (2).

Button configurations

One of the interesting phenomena observed on Callisto is button-like formations that are 80-100 meters high. They are made of water ice and also contain some dark dust. As the ice evaporates the dark matter slides down, moves and accumulates at low levels. Over time all the ice will evaporate until it completely disappears from the impact craters. At the bottom of one of the photos you can see that the evaporation has stopped in the planes that appear in it (16).


Due to the thinness of the atmosphere, there are no winds on Callisto, yet in several photographs it is possible to notice that erosive activity has occurred on its surface. In photo 0876PIA some of the craters do not have a sharp structure on their sides. The large craters visible in it, one of them with a diameter of 60 km and the other with a diameter of 30 km (17). Another photograph taken from a distance of 138 km from the ground shows a light and spiky area with dark dust. It is seen that this area has undergone a slow but active process of erosion. The explanation for this is that part of the ice sublimated and left behind the dust that was attached to it. The accumulation of dust absorbs enough heat from the sun to heat the surrounding ice and allows the sublimation process to continue (18).

Internal structure

Callisto's gravity measurement showed that it probably has a homogeneous internal structure. 60% of it is rock and 40% compressed water ice. It seems that within Callisto there is no internal separation of matter. This estimate is consistent with the fact that the Moon has no internal magnetic field, indicating that it has not experienced a phase of high heating necessary to separate the rock and metallic elements from the light ice (19).

ocean water

The researchers noticed that each time the spacecraft passed by Europa and Callisto, the strength and direction of Jupiter's magnetic field changed slightly. Both moons appear to generate electric currents near their surface as they pass through Jupiter's magnetic field, much like an electric motor generates an electric current. In order for there to be an electric current there must be some kind of conductor. The water ice that covers Europa and Callisto will not cause this because we are not a good conductor. Salt water, on the other hand, is a good conductor, which has led to the line of thought that beneath the surface of Callisto there is an ocean. While ionized molecules in the atmosphere are certainly a good conductor, Callisto's atmosphere is too thin to create this effect. It is estimated that the ocean of water is 16 km below the surface of the earth. The obvious question is what heats this water? A possible answer is radioactive elements in the nucleus (20). Geological evidence that can support this hypothesis is the Valhalla basin. Such a layer of water would have dissipated the shock waves created by the impact that created this basin. The lack of hills and grooves on the other side of Callisto (Antipode) is consistent with this possibility (21). In the Antipode of large craters on the Moon and Mercury, grooves and hills called Antipode Terrein are found and are attributed to shock waves originating from the craters on the other side of these bodies (22).


Around Callisto there are plasma waves, although, unlike Ganymede, it does not have a magnetosphere or an internal magnetic field. The electron density around this moon is higher than the magnetic field of Jupiter at this distance from the planet itself, which indicates that Callisto is a definite source of a plasma generator created in this place. Callisto's thin atmosphere likely generates this plasma. It is similar to the hydrogen cloud surrounding Ganymede since the electron density in both moons is similar (19).


1. Carlson RW-"A tenuous Carbon Dioxide atmosphere on Jupiter's moon Callisto"
Science Vol. 283 pp. 820-821 5.2.1999

2. Schenk PM- "The geology of Callisto" Journal Of Geophysical Research Vol. 100 no. E9 pp. 19, 023- 19, 040 25.9.1995

3. "Callisto craters by descending diameter (km)

4."Galileo flyby reveals Callisto's bizarre landscape" 22.8.2001

5.PIA09258: Capturing Callisto

6.Rogus FH-The giant planet Jupiter Cambridge University Press 1995 pp. 383-384

7. Strom RG et al - "Crater population on Ganymede and Callisto" Journal Of Geophysical Research Vol. 86 A10 pp. 8659-8674 30.12.1981

8.PIA091298: Global variation on Callisto

9.PIA01629 : Textured terrain Callisto's Asgard basin

10.PIA00517: Asgard impact structure on Callisto

11.PIA01648: Impact craters on icy Callisto Doh crater and Asgard

12.PIA01054: Har crater on Callisto

13.PIA00745: Callisto's equatorial region

14.PIA01095: Landslides on Callisto

15.PIA01222: Mass wasting in craters near the south pole of Callisto

16."2001 images releases Jupiter's moon Callisto" 22.8.2001

17.PIA00876: Craters near the south pole of Callisto

18."Gallileo flyby reveals Callisto's bizarre landscape" 22.8.2001

19. "Galileo spacecraft explores Jupiter's moon Callisto: 15.5.1997 recurssors/astronom/galileo/calisto/nature.htm

20. Kenneth C.-A sea on Jupiters Call Isto” 23.10.1998

21. "Opposite side of Callisto from Valhalla impact" 29.11.2001

22."ocean inside Jupiter moon may have cushioned impact" 29.11.2001

30 תגובות

  1. Hezi isn't going to study anywhere, he just found new, easier places, for his baseless insistence...

  2. Hezi,

    From your lack of response I understand that you listened to my advice and decided to turn to academic physics studies


  3. Hezi,
    Your question was how it is possible to prove that there is a distortion of space and time and it is not all about the attraction of light by a large mass.
    I gave you a partial answer to this question - the attraction of light particles by a heavy mass as obtained from Newton's theory does not correspond to the observational results but rather predicts a deviation of about half of the true value.
    Beyond that, I cannot give you a full explanation of the question of how Einstein came to the strange idea of ​​the curvature of space by large masses within the framework of a talkback, the subject is taught in a not easy course for master's and third degree students in physics, lasts over an entire semester and requires a lot of prior mathematical knowledge I suppose which you don't have (differential geometry, tensor calculus, etc.).
    I and I think also Michael, we answered you partially already in the past and I will repeat it again - there are several observational proofs that prove that this is a curvature of space as predicted by Einstein's theory and not just a curvature of the path of light under the influence of gravity as Newton's theory can be interpreted in a strange way. The three well-known explanations and proofs are also called the classic experiments of the theory of relativity and these are:
    1. The precession of the perihelion of Mercury - according to Newton's theory, the planet Mercury is supposed to move in an elliptical orbit, in practice it moves in an orbit close to an ellipse when the perihelion (the point closest to the sun in the orbit) changes slightly from rotation to rotation, the theory of relativity predicts exactly the degree of change.
    2. Redshift in the presence of a gravitational field - photons emitted from a massive object are redshifted. There is no explanation for this in Newtonian theory.
    3. The deflection of light rays near a massive object is twice that experienced by an object moving at the speed of light according to Newton (according to Newton of course there is no problem moving at this speed because he did not know what Einstein did know) - the claim that light can be distracted is only because Its approximation to mass exists but is infinitesimal.
    Also, every time the GPS is not wrong in a very significant way, this is another proof that space is indeed curved.

    I don't think that the role of a website is to answer only to bored professors and it is true that the website (and therefore also its readers) will appeal to all people who do not see physics as a profession but do want to understand something. That's why I answered you in this case with a detailed answer as much as possible.
    I think that if you just want to know broadly, at the level of popular science, what the physicists claim on the subject, then I have given you a basis from which you can continue reading to know more (start with Wikipedia). If you want to know more in detail (and of course you will because you want to expose the scientific community to its mistakes), you will have to start studying physics at a slightly higher level - you will start in high school, and from there you will move to a first-second-third degree, after that there is a chance that you will understand enough to question You will still feel the need for it.
    Before that, doubting is not healthy skepticism but groundless obstinacy.

  4. pleasantness,

    Can't you see that I'm not even religious?

    I asked questions above, but she ignored them.
    that you say what you say,
    It's not science, it's smelling...

    I already thought you were a serious person...

  5. I agree with Noam's response.
    If this satisfies you, then the curvature of the path of light is not as observed from matter according to Newton's theory, but double of it.
    If not, you will have to study a little more before questioning a proven theory such as relativity.

  6. Chazi the ultra-orthodox,

    Asking the same question twice, without reading a single answer, is a bit excessive.

    It has already been explained to you that light is not attracted to mass but passes through the shortest path in the presence of mass that distorts space-time.
    The question is, are you really trying to understand, or are you just enjoying bashing.

    Zvi will surely answer better than me, but what you are asking is for them to teach you general relativity on top of this site - again, a bit excessive, isn't it?
    The mathematical development of general relativity is complicated and requires a broad knowledge of mathematics, without which it is impossible to explain to you how they "arrived at the formula"

  7. deer,

    Can you explain how you arrived at this formula?

    I am a skeptic by nature.
    And I have the feeling that there is a trap here.

    A- It is clear to me that light behaves as matter,
    And it is attracted to a large mass, like any substance.

    The question: How is it possible to prove that a distortion of space and time is created and it is not just about the attraction of light by a large mass?

  8. Michael, are you sure?

    I am quite convinced that Prof. Sabramish was nominated for a Nobel Prize several years ago for the development of this theory - together with Moshe's "everything is in consciousness" theory or Hazi's "what is random evolution without anti-alien matter" theory (both from Cambridge).

  9. deer:
    You probably don't know what the theory of pressure differences is that Noam talked about (and it's not your duty).
    The theory that Noam joked about has not been used to this day and all it has is an enthusiastic sales agent.

  10. Of course they didn't pay attention, for two reasons:

    1. The pressure theory was not used in the 70s (as far as I know)
    2. There is no need to refer to it (or ability, since it is very non-quantitative).

    The statement that the theory of pressure difference is one of the two cornerstones of modern physics is also not quite true (for now...).

  11. deer,

    It was not a serious question - there is no way that Penrose and Hawking were referring to Yehuda Sabdarmish's theory

  12. I don't understand enough about these two theories, but if I'm not mistaken, Penrose and Hawking tried to reconcile these two views back in the 70s and managed to achieve partial achievements. Since then, most scientists are afraid to get into complicated and complex issues like these.

    Apparently, the theory of relativity is still far from perfect, as evidenced by its complete incompatibility with two of the cornerstones of modern physics - quantum theory and, above all, the theory of pressure differences.

  13. deer,

    One thing I did not understand:
    Everything you explained above is in complete contradiction to Yehuda Sabdarmish's theory of pressure differences.

    How do you explain that???

  14. Einstein's theory is not "beautiful literature" but physics, with equations and numbers).
    The Schwarzschild or Kerr matrix are a specific solution of the Einstein equation (therefore they do not contain other physics).
    Einstein's equation gives the curvature of space as a function of the distribution of matter and energy in it - if you assume a very simple distribution in which all matter is concentrated in a closed space and in a radial form - the solution you get is the Schwarzschild hammer - if you add rotation you get a cold hammer. There are only two other solutions for black holes (a charged black hole and a charged and rotating black hole) and managed to show that this is sufficient to describe all possible black holes (no hair theorem).

    The metric is actually how the distances change as a function of changing coordinates (the simple metric known to everyone is the Pythagorean theorem) - what I wrote down is not the Pythagorean theorem because the presence of mass causes the metric to not be Euclidean (in addition, we also introduced time into the equation, which changes the situation even more).

    Your claim that the mass of the black hole at the center of the galaxy is unknown is incorrect or rather inaccurate. We know that it weighs more than a gram and less than a billion solar masses, so to say that we know nothing is not true. We don't know how to say its exact mass - it is clear, but it is of the order of about 5 million solar masses and that is what is important.
    Go back to comment number 10 (where I worked based on a little more than 6 million solar masses) and you will understand that even with a mass 10 times greater (really out of the question), i.e. a Schwarzschild radius 10 times greater than what I wrote, the nearest star is still at a distance 1000 times greater than the Schwarzschild radius, meaning that the curvature of space at these distances has no effect and the calculations according to Newton's theory will be very accurate.

    And again - there is no problem calculating the curvature in space given that the mass distribution is known, the statement that the mass curves the space is not some kind of poetic statement but a physical quantitative prediction that has been proven on countless occasions.

  15. Beauty…

    (It is strange that Einstein himself did not offer a beacon for this)

    Since I'm not a mathematician,
    You will only have to explain (without going into the details of the symbols in the beacon)
    What are the units you use for the time warp and the space warp.

    The most important: how they calculated the distortion in the center of the galaxy,
    While the mass of the black hole is unknown.

    Assuming you have mastered the subject, I would be happy to continue…

    I hope you will be consistent and not suddenly disappear...

  16. deer:
    Regarding your response - I didn't understand what "chest" is.

  17. Of course - the part concerning dphi should be replaced by sin(theta)dphi]^2]

  18. You're 100% right,

    There must be such a formula and it is called the Schwarzschild hammer for a simple black hole or the Kerr hammer for a rotating black hole. You of course know this and you just happened to forget, so I will remind you of the Schwarzschild hammer (Kerr, as you know, is very long and tedious):

    From the matrix you can see that when M

  19. deer,

    Physics is not beautiful literature...

    Since Einstein's theories are considered the pinnacle of physics,
    There must be a formula that calculates the curvature of space and time near a black hole.

    Since the black hole at the center of the galaxy is of the supermassive type,
    That is, having an extremely large mass,
    Physics must give us a formula how to calculate the curvature of time and space.
    Otherwise this is not physics but a bluff...

  20. Hezi

    1. Space and time are curved near a black hole (or near any massive object) in a known way. This has been proven on a thousand different occasions and no person who understands the field gives evasive answers to people who know a certain required basis.

    2. The size scales characteristic of the curvature of space in a significant way, so that he saw different relativistic effects than those predicted by Newton's gravity - are the distance scale of the Schwarzschild radius of the black hole.
    For the sun, the Schweichschild radius is about 3 km. For the black hole in the center of the galaxy, its size is about 20 million km, which is about 0.1 AU (where AU is the distance from the Sun to the Sun).
    The stars closest to the black hole (observed, which is probably what you saw) are close to a milliparsec SDG from the black hole, i.e. - about 2000AU from the black hole.
    That is, the stars are approximately 10,000 times farther away than relevant distances for any prominent relativistic effect, so it is certainly possible to watch the whole story with the assumptions of classical mechanics and even with what you say the scientists do not understand the issue of the curvature of space (which is of course absolutely not true), then in this case it is possible to manage without the help of general relativity At a pretty good level.
    The way to know that what is there is a black hole is (among other things) to notice that in the place where (according to the orbits of the stars) there should be a mass of about 6 million solar masses, nothing is seen.

  21. I wrote it as a joke. That's really not the point. 26 or 27 thousand...

    I'm trying to check the theory of relativity.

    As I wrote earlier,
    According to the theory,
    Space and time are supposed to curve in the vicinity of the black hole.

    But no one talks about it…

    How is it possible that they curve but do not affect our vision,
    And we are able to see the fantastic accuracy I mentioned earlier?
    And all this without knowing the mass of the black hole?

    (When I asked Yael here about this subject by several months, she claimed that it was taken into account...)

  22. Chest:
    It is some number between 26 and 27 thousand.
    You have to understand that people don't take troublemakers like you into account when they write. They are trying to point out the main point.
    You talked about thousands of light years and I corrected your mistake but an order of magnitude 10 times what is between me and you.

    You wonder how all kinds of things are possible but be careful with all your heart not to learn even the last zero of the profession.
    What exactly are you expecting?
    Let the scientists come and apologize to you for being smarter and more educated than you?

  23. incidentally,

    The article mentions that our distance from the center of the galaxy is 26.000 light years.

    One thousand light years between you and me, what are they...

  24. Sorry, correction:

    It was about tracking a star moving around the center of the galaxy,
    and according to its change in velocity as it orbits the black hole,
    They knew there was a black hole there.

    In the article, a space scientist was interviewed who claimed that their ability to be accurate in space observations,
    It is of the order of magnitude of an observation between the east and west coast of the USA
    and the ability to distinguish a displacement of 2 cm.
    This is truly an amazing ability.

    I return to the main point:

    How is this ability possible?
    When we do not know and cannot measure what is the mass of the black hole in the center of the galaxy, and the extent of its influence on the light observed from there?
    How does the story of the "distortion of time and space" fit in with this matter?
    How was it measured, and how is it possible to make the above observations without knowing and measuring the above?

    I again claim that there is a hiding of the truth in this matter...

  25. By the way, my chest:
    Of course there is no confusion on the subject among the scientists.

  26. They probably didn't express themselves there in such a clear way, but the scientists actually didn't wait for the eruption but for them to see it here.
    After all, even if an eruption happened right now - they wouldn't see it until after 27000 years.
    The fact that we are about to see an eruption can be predicted because some time before we see the signs that precede that eruption (signs that were created 27000 years ago and reached us only recently).

  27. It is true that the question is not related to the article, but it was the closest to the topic...

    Since I appreciate that articles in National Geographic are reliable,

    Scientists were shown there who were waiting to document an eruption,
    There was coordination between several groups of researchers in different countries.

    They show the jubilation when they finally noticed the outbreak...

    In any case, it seems strange to me that the issue of the difference of many light years was ignored in the article,
    Compared to the observed place…

    As I have written here several times,
    I have doubts about (at least parts of) relativity.

    It is clear to me that there is confusion on this issue even among the scientists.

    To mention, I asked Yael here (who writes articles here)
    And after she had to "find out" she replied evasively...

  28. Chest:
    Your question is not related to the article.
    Our distance from the center of the galaxy is 27,000 light years.
    It's really impossible to know when there will be an eruption in the center of the galaxy - not only with an accuracy of minutes but even with an accuracy of tens of thousands of years.
    On the other hand - I don't believe anyone said it was possible.

  29. Wonders about observations of the center of the Milky Way:

    Our distance to the center of our galaxy is at least several light years,
    Watching a National Geographic program about the study of the center of the galaxy
    It makes me wonder: how can you know with minute precision when there will be an eruption in the center of the galaxy,
    As claimed in the article?

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