Callisto (moon)

Galileo Galilei

Callisto ( from the ancient Greek name Καλλίστη KALLISTE " the fairest " = Callisto, a mistress of Zeus ) ( Jupiter IV, Callisto ) with a diameter of 4821 km is the second largest and outermost of the four large moons of Jupiter and the third-largest moon in the solar system.

• 6.1 Possible manned missions

History

Kallistos discovery is the Italian scholar Galileo Galilei attributed to the simple set up his telescope at Jupiter in 1610. The four large moons Io, Europa, Ganymede and Callisto are also referred to as the Galilean moons.

It was named after the moon Callisto, a lover of Zeus in Greek mythology. According to legend, Callisto and her son Arcas were later transformed into bears and moved to the starry sky. Kallisto is therefore twice to see the sky as the constellation Ursa Major ( the Big Dipper ) and as a moon of Jupiter.

The name Kallisto has already been suggested by Simon Marius soon after its discovery, but could not prevail over time. Only in the middle of the 20th century he came again into use. Before moons were usually numbered with Roman numerals and Callisto denoted by Jupiter Moon IV, because the numbering was originally made ​​after the variable sequence of orbits.

The Galilean moons are so bright that they can already be observed with binoculars or a small telescope.

Orbit and rotation

Callisto orbits Jupiter at an average distance of 1.833 million km in 16 days 16 hours and 32.2 minutes. Your web has an eccentricity of 0.007 and 0.51 ° inclined to the equatorial plane of Jupiter.

When the outermost of the Galilean moons Callisto is removed from the orbit of the next inner and larger Ganymede over 800,000 km. In relation to the orbital period of Ganymede to Callisto moved in a 3:7 orbital resonance, in contrast to the 1:2 resonance between the respective adjacent inner three large moons.

Callisto rotates in 16 days 16 hours and 32.2 minutes on its own axis, thus showing how the Earth's Moon and the other inner moons of Jupiter, a tidally locked to.

Physical Properties

Callisto has an average diameter of 4821 km, making it almost as large as the planet Mercury ( 4878 km ). Their density is slightly smaller than that of Ganymede, but significantly smaller than those of the two other Galilean moons Europa and Io with about 1.83 g/cm3.

She has compared to the other Galilean satellites, a very dark surface with an albedo of 0.2, ie only 20 % of the incident sunlight is reflected. The surface temperature of -139 ° C in the average.

Surface structures

Callisto has the highest density of impact craters in the solar system. Crater formed during the impact concentric annular elevations characterize the surface; major mountain ranges are not available. This suggests that Kallistos surface is mainly composed of water ice. The icy crust has yielded over geologic time, with older craters and mountain ranges were leveled.

Two giant impact basins, surrounded by concentric ring walls, are the most striking structures on Callisto. The largest pool, Valhalla, has a diameter of 600 km, a bright central region and rings that extend over 3000 km. The basin Asgard expands total of over 1600 km. Another interesting structure is Gipul Catena, a chain of impact craters, which runs as a straight line on the surface. The structure was apparently caused by a celestial body, which was as the comet Shoemaker- Levy 9 torn before impact by the tidal forces of Jupiter.

The age of the surface of Callisto is dated to 4 billion years. She was not subjected to major changes since the early days of the solar system, which means that the moon was geologically active for longer than this period. Unlike neighboring Ganymede with its striking surface Callisto has no evidence of plate tectonics, although it is about the same size. Their geological development was obviously much easier to run, or completed after a relatively short time, while in the other Galilean satellites took place more complex operations.

The visible surface is on a layer of ice, which has an estimated thickness of 200 km. Among presumably located approximately 10 kilometers of deep ocean of liquid salt water, and magnetic measurements indicate the Galileo spacecraft. A further indication of liquid water is the fact that on the opposite side of the crater Valhalla no fractures and dislocations are visible, as can be observed on massive bodies such as the Earth's moon or the planet Mercury. A layer of liquid water has apparently mellowed the seismic shock waves before they moved through the lunar interior.

Internal construction

The interior of Callisto is built accordingly from about 60% silicate rock and 40% water ice, which increases with increasing depth of the silicate component. From compositionally Callisto is similar to Saturn's moon Titan, and Neptune's moon Triton. Therefore your mass is despite its size just under a third of the mass of Mercury, and is about 30 % greater than the mass of Earth's moon.

Atmosphere

Recent observations indicate that Callisto has an extremely thin atmosphere of carbon dioxide.

Magnetic field

The probe Galileo had a weak magnetic field at Callisto measured at their flybys, the strength of which varies as the moon moves through the extremely strong magnetosphere of Jupiter. This indicates the presence of an electrically conductive liquid, such as salt water, below Kallistos icy crust.

Exploration by special missions

The exploration of Callisto by space probes began in the years 1973 and 1974 with the Jupiter flybys of Pioneer 10 and Pioneer 11, Voyager 1 and Voyager in 1979 were 2 first make precise observations of the moon. However, the majority of knowledge about Callisto is from the Galileo orbiter, which in 1995 reached the Jupiter system and during the next eight years, several flybys of Jupiter led full moon.

For 2020, the space agencies NASA and ESA had the common Europe proposed Jupiter System Mission / Laplace, which provided at least two Orbiter, which respectively enter into orbit around Europa and Ganymede, and should explore the entire Jupiter system with a revolutionary draft.

NASA, who wanted to build the JEO, but got out of the project. However, the ESA realized the JGO with a slightly different mission planning as JUICE. JUICE to Engage in 2030 and two flybys of Europe and 12 flybys of Callisto in 2032 in orbit around Ganymede after their arrival at Jupiter. Since the NASA probe is omitted, the two Europa flybys were included in the mission plan for JUICE.

Possible manned missions

At least since the 1980s Kallisto is considered a possible target of manned space flight for after a manned flight to Mars, because it is outside the radiation belt around Jupiter.

In 2003, NASA published a study entitled Revolutionary Concepts for Human Outer Planet Exploration ( German revolutionaries about concepts to explore the outer planets by humans) in such a mission - to start from 2045 - discussed in various variants. The reasons for the choice of Callisto as a target were called to earth for a stable geology and the comparatively small distance. Furthermore, the ice on the surface of obtaining water and fuel could be used. As a further advantage, the short distance to Europe was called, this would allow the crew, robots in this very interesting scientifically moon with low-latency remote control, without being exposed to the radiation.

As a prerequisite for the implementation of the mission, the study identifies an intensive exploration by unmanned probes from about 2025. Depending on the selected and available drive the real mission would start with one to three spaceships, each of the crew and the rest of the ground station, a plant water extraction (in- situ Resource Utilization ) and transporting a reactor for power generation. The mission duration is between two and five years, with a length of stay 32-123 days on the moon, where there is no connection between the air and the length of stay due to the different driving techniques.

The study concludes that a manned mission Kallisto from the year 2045 is possible in principle and identifies a number of technologies that would be developed by then. However, the authors point out that these technologies are partially required for missions to Earth's moon and Mars, or at least be an advantage.