Callisto (moon)


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Callisto
Callisto
Jupiter's moon Callisto, recorded by the Galileo spacecraft in May 2001
Central body Jupiter
Properties of the orbit
Major semi-axis 1,882,700 km
Periapsis 1,869,500 km
Apoapsis 1,895,800 km
eccentricity 0.007
Orbit inclination 0.51 °
Orbital time 16,689 d
Mean orbital velocity 8.20 km / s
Physical Properties
Albedo 0.19
Apparent brightness 5.7 likes
Medium diameter 4820.6 km
Dimensions 1.076 x 10 23 kg
surface 7.2 × 10 7 km 2
Medium density 1.830 g / cm 3
Sidereal rotation 16,689 days
Axis inclination 0 °
Acceleration of gravity on the surface 1.235 m / s 2
Escape speed 2400 m / s
Surface temperature 80 ± 5 - 134 ± 11 - 165 ± 5 K
discovery
Explorer

Galileo Galilei

Date of discovery January 7, 1610
Remarks Simply bound rotation.
Callisto has an atmosphere with <10 −6  Pa, mainly carbon dioxide.
Size comparison
Size comparison between Callisto (bottom left), Earth's moon (top left) and Earth (true-to-scale photo montage)

Kallisto (also Callisto or Jupiter IV ) is the fourth moon of the giant planet Jupiter . It is the second largest of the four large moons of Jupiter and, with a diameter of 4,820 km, is the third largest moon in the solar system , only slightly smaller than the (albeit much more massive) planet Mercury .

Callisto belongs to the ice moons type . It is the most crater-rich body in the solar system.

Callisto is the outermost of the large moons I – IV, all of which are so bright that you can see them with binoculars .

It is five times as far from Jupiter as the Earth's moon is from Earth , but due to the enormous mass of the planet it only has 16 days orbital period. At the next inner moon III ( Ganymede ) it is 7.2 days.

history

Callisto's discovery is attributed to the Italian scholar Galileo Galilei , who pointed his simple telescope at Jupiter in 1610 . The four great moons Io , Europa , Ganymede and Callisto are also known as the Galilean moons .

The moon was named after the nymph Kallisto ( ancient Greek Καλλιστώ derived from καλλίστη KALLISTE "the fairest"), a lover of Zeus from the Greek mythology . According to legend, Callisto and her son Arkas were later turned into bears and transported to the starry sky. Callisto can therefore be seen twice in the sky, as the constellation Great Bear (Big Dipper) and as the moon of Jupiter.

Unlike the Earth's moon, Callisto, like all satellites in the solar system, has no official astronomical symbol or one that is commonly used.

The name Kallisto was suggested by Simon Marius shortly after its discovery, but it did not catch on for a long time. It was not used again until the middle of the 20th century. Previously, moons were usually only numbered with Roman numerals and Callisto was referred to as Jupiter's moon IV , since the numbering was originally based on the order in which the orbits were sized.

Orbit and rotation

Callisto orbits Jupiter at a mean distance of 1,882,700 km in 16 days, 16 hours and 32 minutes. Its orbit has an eccentricity of 0.007 and is inclined 0.51 ° to the equatorial plane of Jupiter.

As the outermost of the Galilean moons, Callisto is over 800,000 km away from the orbit of the nearest inward and slightly larger Ganymede. In relation to its orbital time, Callisto moves in a 3: 7 orbital resonance , in contrast to the 1: 2 resonances between the three adjacent inner large moons.

Callisto rotates exactly once during its orbit (16.689 days) and thus, like the Earth's moon and the inner moons of Jupiter, has a bound rotation .

Physical Properties

Callisto has a mean diameter of 4821 km and is almost as big as the planet Mercury (4878 km). At about 1.83 g / cm³, their density is somewhat smaller than that of Ganymede, but significantly smaller than that of the other two Galilean moons Europa and Io.

Compared to the three other Galilean moons, it has a darker surface with an albedo of 0.2 (only 20% of the incident sunlight is reflected ). Therefore it has the lowest brightness with 5.6 mag, less than the 35% smaller Europe . The surface temperature is on average −139 degrees Celsius.

Surface structures

The giant Valhalla crater, captured by Voyager 1 in 1979

Callisto has the second highest density of impact craters in the known solar system after Saturn's moon Phoebe . In addition to the craters, only a few concentric, ring-shaped elevations formed during the impacts shape the surface; larger mountain ranges are not available. From this one concludes that the surface of Callistus is mainly composed of water ice with only a small amount of rock. The ice crust has given way over geological time, leveling older craters and mountain ranges. The largest named and recognized crater Heimdall measures 210 km in diameter and is located in the north on the central meridian of the hemisphere facing Jupiter.

The region around the Asgard impact basin , recorded by the Galileo space probe

The most striking structures on Callisto are two huge impact basins, surrounded by concentric ring walls. Valhalla has a diameter of 600 km, a bright central region and rings that extend over 3000 km. The somewhat smaller Asgard basin extends over 1,600 km. One unusual structure is the Gipul Catena , a chain of impact craters that runs in a straight line across the surface. It was apparently caused by a celestial body that, like Comet Shoemaker-Levy 9 , was torn apart by the tidal forces of Jupiter before the impact . Similar catena structures can be found on the neighboring moon Ganymede, the largest of which, Enki Catena, consists of 13 craters and is 160 km long.

The age of the surface of Callistus is dated to 4 billion years. It has not undergone any major changes since the early days of the solar system, which means that the moon has not been geologically active since that time. Unlike the neighboring Ganymede with its striking surface, Callisto shows no signs of plate tectonics , although it is almost the same size. Their geological development was evidently much simpler and completed after a relatively short time, while more complex processes took place in the other Galilean moons.

Ice deposits and ocean

The visible surface lies on a layer of ice that is estimated to be 200 km thick. Underneath there is probably a 10 km deep ocean of liquid salt water, as indicated by magnetic measurements from the Galileo space probe . Another indication of liquid water is the fact that on the opposite side of the Valhalla crater there are no fractures and faults visible, as can be seen on massive bodies such as the Earth's moon or the planet Mercury . A layer of liquid water may have dampened the seismic shock waves before they moved through the interior of the moon.

internal structure

Inner structure of Callisto: The inside consists of ice and rock, above it a possible ocean, on the surface there is a layer of ice.

The inner Kallistos is made up of about 60% silicate rock and 40% water ice , whereby the silicate content increases with increasing depth. In terms of their composition, Callisto is similar to the Saturn moon Titan and the Neptune moon Triton . Despite their size, their mass is therefore just under a third of the mass of Mercury and is about 30% larger than the mass of the Earth's moon .

the atmosphere

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

Magnetic field

During its flyby, the Galileo probe measured a weak magnetic field at Callisto, the strength of which varies as the moon moves through the extremely strong magnetosphere of Jupiter. This suggests the presence of an electrically conductive liquid, such as salt water, beneath Callisto's ice crust.

Exploration through probe missions

Spacecraft exploration of Callisto began in 1973 and 1974 with the Jupiter flybys of Pioneer 10 and Pioneer 11 . In 1979, Voyager 1 and Voyager 2 were able to make more accurate observations of the moon for the first time. However, most of the knowledge about Callisto comes from Galileo - Orbiter, the 1995 reached the Jupiter system and several flybys fully introduced on Jupiter's moon during the next eight years.

For 2020, the space agencies NASA and ESA had proposed the joint Europa Jupiter System Mission Laplace , which provided for at least two orbiters, each of which would enter an orbit around Europa and Ganymede and would explore the entire Jupiter system with a revolutionary depth.

However, NASA, which wanted to build the Jupiter Europa Orbiter , withdrew from the project. Meanwhile, ESA is realizing the Jupiter Ganymede Orbiter with slightly modified mission planning as JUICE . JUICE is slated to enter orbit around Ganymede after arriving at Jupiter in 2030 and two flybys of Europe and 12 flybys of Kallisto in 2032. Since the NASA probe is no longer required, the two European flybys have been included in the mission plan for JUICE.

Possible manned missions

Since the 1980s at the latest, Kallisto has been a possible target for manned space travel after a manned flight to Mars , as it lies outside the radiation belt around Jupiter.

In 2003, NASA published a study entitled Revolutionary Concepts for Human Outer Planet Exploration (German about Revolutionary Concepts for the exploration of the outer planets by humans ), which discussed such a mission - starting from 2045 - in different variants. The reasons given for choosing Callisto as a destination were, on the one hand, the stable geology and the comparatively short distance to the earth. Furthermore, the ice on the surface can be used to produce water and fuel. Another advantage was the short distance to Europe , which enabled the crew to remotely control robots on this scientifically extremely interesting moon with low latency without being exposed to its radiation.

The study cites intensive exploration by unmanned probes from around 2025 as a prerequisite for carrying out the mission. Depending on the selected and available propulsion system, the actual mission would start with one to three spaceships, one for the crew and the rest for the ground station for water extraction ( in-situ resource utilization ) and a reactor for energy generation. The duration of the mission is between two and five years with a duration of 32 to 123 days on the moon, whereby there is no connection between the flight and the duration of stay due to the different drive technologies.

The study comes to the conclusion that a manned Callisto mission is basically possible from the year 2045 and names a number of technologies that would have to be developed by then. However, the authors point out that some of these technologies are also required for missions to the Earth's moon and Mars, or are at least beneficial.

Web links

Commons : Kallisto  - album with pictures, videos and audio files
  • Callisto in the Gazetteer of Planetary Nomenclature of the IAU / USGS.

Individual evidence

  1. a b Jovian Satellite Fact Sheet. At: NASA.gov. Vestibules, path speed, surface and brightness are calculated from this.
  2. Callisto in the Gazetteer of Planetary Nomenclature of the IAU (WGPSN) / USGS ; accessed on September 28, 2016.
  3. JUICE. Exploring the emergence of habitable worlds around gas giants. Assessment Study Report from December 2011 (Yellow Book), accessed on September 9, 2012 (PDF; 39.7 MB).
  4. James Oberg: Where are the Russians Headed Next? In Popular Mechanics , Oct 1982, p. 183.
  5. Patrick A. Troutman, Kristen Bethke, Fred Stillwagen, Darrell L. Caldwell Jr., Ram Manvi, Chris Strickland, Shawn A. Krizan: Revolutionary Concepts for Human Outer Planet Exploration (HOPE). (PDF; 4.5 MB). Published in February 2003.
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Ganymede Callisto
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