Callisto is the second largest moon of Jupiter. In this article on Callisto facts we are going to learn some incredible facts about this amazing celestial object that was first discovered by Galileo Galilei.
NASA says it is interesting because of the possibility of life-sustaining characteristics that Callisto has to offer.
So, without further delay, let us start exploring this celestial object and find out the surprises it holds for us. Are you ready? Of course, you are!
Amazing Callisto Facts: 1-6 | Callisto in Numbers
1. Callisto was discovered in 1610.
2. Callisto is 2.6 times smaller compared to our Earth.
3. The average orbit distance of Callisto from Jupiter is 1,882,700 kilometers.
4. The mean orbit velocity of Callisto is 29,531.6 kilometers per hour.
5. The equatorial radius of Callisto is 2,410.3 kilometers.
6. The equatorial circumference of Callisto is 15,144.4 kilometers.
Amazing Callisto Facts: 7-12 | Callisto in Numbers
7. The total volume of Callisto is 58,654,577,603 km3.
8. Density of Callisto is 1.834 g/cm3.
9. Total mass of the satellite is 107,593,737,963,819,000,000,000 kg.
10. Total surface area is 73,004,909.27 km2.
11. The surface gravity of Callisto is 1.236 m/s2.
12. Escape velocity of Callisto is 8,787 km/h.
Amazing Callisto Facts: 13-18 | Callisto in Numbers
13. The exact date of discover of Callisto was January 7, 1610.
14. Callisto has a surface temperature of -139°C.
15. Callisto takes 16.69 Earth days to orbit around Jupiter.
16. Callisto is of nearly the same size as that of the planet Mercury. Equatorial diameter of Callisto is 4,820.6 km whereas, the equatorial diameter of Mercury is only 58.40 km more than that of Callisto.
17. In short, Callisto is 99% the size of Mercury.
18. Despite being nearly the same size as that of Mercury, Callisto has only 1/3rd the mass of Mercury.
Amazing Callisto Facts: 19-24 | Callisto in Numbers
19. While the mass of Callisto is 107,593,737,963,819,000,000,000 kg, the mass of Mercury is 330,104,000,000,000,000,000,000 kg.
20. Callisto sits at a distance of 628,300,000 kilometers from our Earth. It is 180 times further away from Earth as compared to our Moon from our Earth.
21. Callisto is 1.8 times farther away from Jupiter compared to Ganymede.
22. Callisto is 2.8 times farther away from Jupiter compared to Europa.
23. Callisto is 4.5 times farther away from Jupiter compared to Io.
24. Did you know that Callisto has an orbital eccentricity of 0.0074? It means that Callisto has a nearly circular orbit around Jupiter.
The orbital eccentricity of any celestial object is a parameter which is used for determining the amount of deviation of the orbit of one body around another body from being a perfect circle. The parameter value can either be 0 or 1 or anything between 0 and 1. The parameter can also be greater than 1. In case the parameter is 0, the orbit is perfectly circular. In case the parameter is 1, the orbit is parabolic escape orbit (or elliptical orbit) while a value greater than 1 means the orbit is a hyperbola.
Amazing Callisto Facts: 25-30 | About Callisto
25. Callisto is a Jovian moon. In simple words, it is a satellite of our Solar System’s largest planet – Jupiter.
26. It is a Galilean moon. It is so called because it was discovered by Italian astronomer Galileo Galilei.
27. It is not the only Galilean moon. There are in total four Galilean moons. The other three are Ganymede, Europa and Io – all three are Jovian moons.
28. Galileo was not the only person who observed Callisto in 1610. There was yet another person who independently observed the moon. His name was Simon Marius. As a matter of fact, Simon Marius spotted Callisto before Galileo.
29. Of the four Galilean moons, Callisto is the Second Largest Galilean moon. So, it is the second largest moon of Jupiter because, the Galilean moons are the largest moons of Jupiter.
30. Callisto is also the Third Largest moon to be found in the entire Solar System. The Largest moon of the entire Solar System is Ganymede (Jovian moon). The Second Largest moon of the entire Solar System in Titan (the moon of Saturn).
Amazing Callisto Facts: 31-39 | Naming
31. Callisto gets its name from Greek mythology.
32. In Greek mythology, Callisto was a nymph and one of the many lovers of Zeus. Some sources say that Callisto was the daughter of Lycaon – the king of Arcadia).
33. It was Simon Marius who suggested the name ‘Callisto’ soon after the discovery of the moon.
34. However, Marius actually attributed the suggestion to another famous German astronomer – Johannes Kepler.
35. Unfortunately, the current names of the Galilean satellites actually fell out of favor for very long until they were finally revived somewhere in the middle of the 20th century.
36. Before the current names were revived in mid-20th century, the Galilean moons were called by the Roman numerical designation.
37. According to Roman numerical designation, Callisto’s name was Jupiter IV.
38. It was Galileo himself who introduced the Roman numerical designation.
39. When it comes to scientific writing, the adjectival form of the name is used. There are two adjectival forms – Callistoan and Callistonian.
Amazing Callisto Facts: 40-44 | Formation of Callisto
40. It is a popular notion held by the scientific community that Callisto and all other Jovian moons were formed in the disk of materials that were left over from the formation of the giant planet Jupiter.
42. Scientists think that ever since the impact craters were formed some 4 billion years ago the moon had little to no geological activities like tectonic shifting or volcanic eruptions.
43. The reason for such assumption is that the impact craters are still visible.
44. It is because of the absence of geological activities, scientists in the past, thought the moon to be boring “ugly duckling moon”. Some called it a “hunk of rock and ice.”
Amazing Callisto Facts: 45-52 | Surface Features of Callisto
45. It appears that the Galilean moon is sprinkled with a lot of bright white dots. What do these dots signify? Most likely they are craters’ peaks with water ice capping.
46. Did you know, Callisto is the most heavily cratered celestial object that we have in our Solar System? There are so many craters on the moon that any new impactor will destroy an existing crater to create a new one.
47. The surface of Callisto is filled with craters. These craters come in various shapes and sizes. Some craters are bowl-shaped. Some craters have multiple rings.
48. The two largest impact craters on Callisto are the multi-ring basins. They are the Valhalla and the Asgard.
49. The bright central region of Valhalla is 600 kilometers in diameter. After that central region are the rings that extend out to 1800 kilometers from the center.
50. The second one – Asgard has a diameter of 1600 kilometers.
51. According to scientists, the ring structures of these craters were not formed during the impact. They were formed after the impact.
52. Scientists theorize that after the impact, the lithosphere went through concentric fracturing because the lithosphere lay on either a soft or a liquid material layer, most likely an ocean.
Amazing Callisto Facts: 53-59 | Structure of Callisto
53. Callisto’s surface is icy and cratered.
54. The average density of Callisto (which is 1.834 g/cm3) suggests that the moon is composed of approximately equal parts of water ice and rocky material.
55. Of course, Callisto is also made of some volatile ice such as ammonia.
56. The Galileo spacecraft has also found that Callisto’s ground has several organic compounds, ammonia, sulfur dioxide, hydrated silicates (containing iron and magnesium).
57. It is interesting to note that the surface of this Galilean moon is quite asymmetric. The trailing hemisphere is brighter compared to the leading hemisphere.
Please note that the leading hemisphere is the hemisphere that faces the orbital motion’s direction and the trailing hemisphere faces the opposite direction.
58. The leading hemisphere is rich in sulfur dioxide while the trailing hemisphere is rich in carbon dioxide.
59. The lithosphere of Callisto is somewhere between 80 km and 150 km thick. Underneath the crust is possibly a salty ocean, which is around 150 to 200 km deep.
Amazing Callisto Facts: 60-66 | Structure of Callisto
60. Why do scientists think there is an ocean underneath the crust? NASA scientists saw that the magnetic field of Callisto gets regular fluctuations as the moon orbits its mother planet (Jupiter).
61. These fluctuations indicated that there were electric currents within Callisto that were stimulated by the magnetic field of Jupiter.
62. Now, if there are electric currents, they have to conduct from somewhere. A thin atmosphere and a rocky surface cannot really conduct the electrical currents.
63. The only possibility is a salty ocean underneath the rocky crust.
64. Scientists also think that the ocean contains some ammonia and other antifreeze material.
65. What is underneath the subsurface ocean? It is nothing but compressed rocks and ice. As depth increases, the amount of rock increases.
66. The density of Callisto and its moment of inertia also indicates that the moon has a small silicate core.
Amazing Callisto Facts: 67-73 | Atmosphere of Callisto
67. Callisto has a very thin or weak exosphere (you can learn more about atmosphere here).
68. NASA’s Galileo spacecraft was the one that detected the exosphere in 1999.
69. The exosphere of Callisto is made of carbon dioxide.
70. Scientists also suspect that the atmosphere has molecular oxygen as well.
71. In 2001, data from Hubble Space Telescope revealed that atmosphere also contains atomic hydrogen.
72. The atmosphere of this Galilean moon is so thin that it will take only 4 days to lose the atmosphere via atmospheric escape.
73. Scientists suspect that slow sublimation of carbon dioxide ice from the icy crust of Callisto constantly replenishes the lost carbon dioxide.
Amazing Callisto Facts: 74-81 | General Facts about Callisto Moon
74. Did you know that the possibility of Callisto hiding a subsurface ocean in it also means that it can potentially harbor life?
76. The reason is simple. Callisto has an icy surface which reflects sunlight way more that our own Moon. So, Callisto appears brighter when viewed through a telescope.
77. Did you know that Callisto is tidally locked to the Jupiter just like our Moon is tidally locked to Earth? What does that mean? It means that only one side of Callisto always points towards Jupiter. The other side never faces Jupiter.
78. Just because Callisto is tidally locked to Jupiter, it doesn’t mean that you can never see more than 50% of Callisto if you stand on Jupiter. Callisto orbits around Jupiter and there are very small changes in the inclination and eccentricity of the orbit.
79. Because of this change in inclination and eccentricity of the orbit, the percentage of Callisto’s face that faces Jupiter changes over a long duration of time (several centuries).
80. So, if you can observe Callisto from Jupiter, over several centuries you can observe more than 50% of Callisto. Did you know we can observe 59% of our Moon because of lunar librations (real or apparent oscillation of Moon that allows the parts near the edges that are usually not visible from Earth to sometimes come into view)?
81. Did you know that Jupiter’s magnetosphere has no impact on Callisto? This means that Callisto is not subjected to rotational energy, orbital energy and tidal friction caused by Jupiter’s magnetosphere.
Amazing Callisto Facts: 82-89 | General Facts about Callisto Moon
82. Because Callisto is not impacted by Jupiter’s magnetosphere, it is not subjected to tidal heating (caused by magnetosphere of Jupiter), which is responsible for melting of surface ice on other three Galilean moons.
83. Considering the diameter of Callisto, it very well qualifies to be classified as a planet. Unfortunately, it will never be classified as a planet because it orbits a planet and not the Sun.
84. Callisto is way beyond the main radiation belt of Jupiter making it a safe environment in outer space for sending human expeditions intended towards exploration of the Jovian system in greater details.
85. NASA intends to go with a manned expedition to Callisto in 2040.
86. Several NASA missions studied this Galilean moon. The missions include Pioneer (10 and 11), Galileo, Voyager (1 and 2), Cassini and the New Horizons.
87. The Galileo mission in particular was tasked with mapping the surface of Callisto in high resolution.
88. ESA or European Space Agency aims towards sending a mission to study the icy moons of Jupiter in year 2022. The mission is called JUICE (Jupiter Icy Moon Explorer). It will study the whole Jovian system but it will focus more on Europa, Ganymede and Callisto and look possible habitable environments.
89. Though Callisto is the second largest moon of Jupiter, in terms of order, it is the 8th moon. In other words, there are 7 more moons between Jupiter and Callisto.
This completes our list of Callisto facts. If you think we have missed any fact, feel free to drop us a comment. Just make sure that you don’t write too scientific for the students to understand.