Europe (moon)


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Europe
Jupiter's moon Europa, recorded from a distance of 677,000 km from the Galileo spacecraft on September 7, 1996
Jupiter's moon Europa, recorded from a distance of 677,000 km from the Galileo spacecraft on September 7, 1996
Central body Jupiter
Properties of the orbit
Major semi-axis 671,100 km
Periapsis 665,100 km
Apoapsis 677,100 km
eccentricity 0.009
Orbit inclination 0.470 °
Orbital time 3.551181 d
Mean orbital velocity 13.74 km / s
Physical Properties
Albedo 0.68
Apparent brightness 5.3 mag
Medium diameter 3121.6 km
Dimensions 4.80 × 10 22 kg
surface 30,600,000 km 2
Medium density 3.01 g / cm 3
Sidereal rotation 3.551 days
Axis inclination 0 °
Acceleration of gravity on the surface 1.32 m / s 2
Escape speed 2040 m / s
Surface temperature 50 - 102 - 125 K
discovery
Explorer

Galileo Galilei

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

Europa (also Jupiter II ) is the second innermost moon on the planet Jupiter . With a diameter of 3,121 km, it is the smallest of the four large moons of Jupiter and the sixth largest moon in the solar system .

Europe is an ice moon . Although the temperature on the surface of Europe reaches a maximum of −150  ° C , measurements of the external gravitational field and the detection of an induced magnetic field in the vicinity of Europe with the help of the Galileo probe suggest that there is a layer of water under the several kilometers thick water ice 100 km deep ocean of liquid water is located.

discovery

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

The moon was named after Europe , a lover of Zeus from Greek mythology . Although the name Europa was suggested by Simon Marius shortly after its discovery , it did not catch on for a long time. It was not used again until the middle of the 20th century. Previously, the Galilean moons were commonly referred to with Roman numerals and Europe was Jupiter II .

The Galilean moons are so bright that you can observe them with binoculars .

Orbit and rotation

Resonance relationships with information relating to Io

Europe orbits Jupiter in a right direction at an average distance of 670,900 kilometers in 3 days, 13 hours and 14.6 minutes. Their orbit is almost circular with a numerical eccentricity of 0.0101. Its orbit points closest to and farthest from Jupiter - Perijovum and Apojovum - each deviate from the major semi-axis by only 1.01% . The plane of the orbit is inclined only 0.470 ° to Jupiter's equatorial plane.

The orbital period of Europe has an orbital resonance of 2: 1 and 1: 2 to its inner and outer neighboring moon ; that is, during two orbits of Europe, Io circles Jupiter exactly four times and Ganymede exactly once.

Like the rest of the inner moons of Jupiter, Europe has a bound rotation ; H. she always turns the same side to the planet.

Structure and physical data

Europe has an average diameter of 3,121.6 kilometers and an average density of 3.01 g / cm³. Although it is clearly the smallest of the four Galilean moons, its mass is greater than that of all the smaller moons in the solar system combined.

The temperature on Europe's surface is only 110  K (about −160 ° C) at the equator and 50 K (about −220 ° C) at the poles.

surface

The currently highest resolution image of the European surface. The section shows an area of ​​1.8 km × 4.8 km. North is right.
The 26 km large impact crater Pwyll

The surface of Europe covers 30.6 million square kilometers, which is roughly the size of Africa. With an albedo of 0.64, it is one of the brightest surfaces of all known moons in the solar system: 64% of the incident sunlight is reflected . The surface is made up of ice . The reddish color is the result of deposited minerals. The surface is exceptionally flat. It is covered by furrows, which, however, are not very deep. Only a few structures that rise more than a few hundred meters above the surrounding area have been identified.

crater

Europe's surface has very few impact craters , which are also only of smaller size. Of the 41 named craters, Taliesin is the largest with a diameter of 50 kilometers. The second largest crater, Pwyll , is 26 kilometers in diameter. Pwyll is one of the geologically youngest structures in Europe. During the impact, light-colored material was ejected from the underground for hundreds of kilometers.

The low crater density is an indication that Europe's surface is geologically very young or renews itself regularly, so that only the impacts of comets and asteroids of the more recent geological past are documented. Calculations of the surface age based on the crater density showed a maximum age of approx. 90 million years. This means that Europe has one of the youngest surfaces among the solid celestial bodies in the solar system.

Furthermore, phyllosilicates on Europe could be detected on the basis of near-infrared images from the Galileo probe . It is believed that they came from an object that struck at a shallow angle, which meant that the impact energy of the impactor was relatively low, so that it could neither completely evaporate nor dig deep into the crust. This discovery is of particular importance because such objects often also carry organic compounds , so-called building blocks of life , with them.

Furrows and ditches

Europe's most striking feature is a network of criss-cross trenches and furrows, called lineae (singular: linea), which cover the entire surface. The lineae have a strong resemblance to cracks and faults on earthly ice fields. The larger ones are about 20 kilometers wide and have indistinct outer edges and an inner area made of light-colored material. The lineae could have been created by cryovolcanism (ice volcanism) or the eruption of geysers from warm water, which pushed the ice crust apart.

These lineae are also for the most part in different places than you would expect. This can possibly be explained by the fact that there is an ocean between the ice crust and the surface of the moon. This could have arisen because due to the eccentric orbit of the moon around Jupiter, its gravitational effect on Europe is constantly changing, so that it is constantly being deformed. Due to these tidal forces, Europe is warming and the ice is partially melting.

When Europe passed the greatest distance from Jupiter in its orbit, hydrogen and oxygen atoms were repeatedly detected over the South Pole. It is believed that they came from the splitting of water molecules released when crevices open and shoot water into space, which falls back to the surface after ascending to a height of 200 kilometers.

Further structures

The Terrain of Conamara Chaos

Another type of surface structure are circular and elliptical structures, called lenticulae ( Latin for lenses). Many are elevations ( English domes), other depressions or flat dark spots. The lenticulae were evidently formed by rising warmer ice, comparable to magma chambers in the earth's crust. The domes were pushed upwards, the flat, dark spots could be frozen meltwater . Chaotic zones, like Conamara Chaos , are shaped like a puzzle made of fragments surrounded by smooth ice. They look like icebergs in a frozen lake.

internal structure

Three-layer model of the inner structure of Europe: The core consists of liquid iron and is surrounded by a mighty mantle of silicate rocks. The outer layer consists of water and is divided into an "ocean" and an ice shell.

Ice crust and ocean

An area with lines, domes, and dark spots; the section is 140 × 130 km

The outer shell of Europe is made of water . Based on measurements of the gravitational field, their thickness between 80 and 170 kilometers was calculated. This outer shell, which can be understood as a crust in analogy to the structure of the earth's body , is differentiated into an outer layer of water ice and an inner layer of liquid water. The inner liquid water layer is commonly referred to as the ocean .

The exact ratio of ice to water in the outer shell is currently unknown. However, there are different hypotheses based on different approaches. Calculations based on evaluations of surface structures arrive at a thickness of the ice envelope of 2 to 18 kilometers. The magnetometric measurements of the Galileo probe suggest that the ocean must be at least a few kilometers thick in order to explain the measurements. On the basis of the same data, other authors conclude that the ocean has a maximum depth of 100 kilometers and the maximum thickness of the ice shell of 15 kilometers. Although Europe is significantly smaller than the earth, the amount of liquid water that occurs there would be more than twice that of the earth's oceans. From about three kilometers below the surface, there could also be bubbles of water trapped in the ice.

The relatively smooth surface of Europe and the structures recognizable on it are very reminiscent of ice fields in polar regions on earth. At the very low surface temperatures, water ice is as hard as rock. The largest visible craters have apparently been filled in with fresh ice and leveled. Detailed recordings show that parts of the ice crust have shifted against each other and broken, creating a pattern of ice fields. The movement of the crust is caused by tidal forces that raise and lower the surface by 30 m. The ice fields should have a certain, predictable pattern due to the bound rotation. Instead, further recordings show that only the geologically most recent areas show such a pattern. Other areas deviate from this pattern with age. This can be explained by the fact that Europe's surface is moving slightly faster than its inner mantle and core. The ice crust is mechanically decoupled from the interior of the moon by the ocean lying in between and is influenced by Jupiter's gravitational forces . Comparisons of images from the space probes Galileo and Voyager 2 show that Europe's ice crust would have to move completely around the moon in around 10,000 years.

Notes on plate tectonics

The images captured by the Voyager and Galileo probes also suggest that the surface of Europa is subject to subduction . Similar to plate tectonics on Earth, mighty ice sheets slowly slide over one another, whereby the plates pushed into the depths melt; In other places, new surface material is created for this. According to the proposed underlying model, Europe's ice sheet consists of two layers. The outer layer of solid ice "floats" on a layer of softer, convection ice. This is the first discovered case of plate tectonics on a celestial body other than Earth.

Sheath and core

Europe is regarded as a prime example of an ice moon , but the share of ice in the total volume of this Jupiter moon is relatively small and its structure corresponds more to that of the terrestrial (earth-like) planets : In the center there is a probably liquid iron or iron-iron sulfide core. This is surrounded by a mantle of silicate rock , which makes up the majority of the satellite's volume.

the atmosphere

Images from the Hubble Space Telescope indicated the existence of an extremely thin atmosphere of oxygen , with a pressure of 10 −11  bar . It is assumed that the oxygen is created by the action of solar radiation on the ice crust, whereby the water ice is split into oxygen and hydrogen . The volatile hydrogen escapes into space, the more massive oxygen is held in place by Europe's gravity .

Magnetic field

When the Galileo probe passed by, a weak magnetic field was measured (its strength corresponds to about ¼ of that of Ganymeds ). The magnetic field varies as Europe moves through Jupiter's extremely pronounced magnetosphere . Galileo's data suggest that there is an electrically conductive liquid beneath Europe's surface , such as an ocean of salt water. In addition, spectroscopic studies show that the reddish lines and structures on the surface are rich in salts such as magnesium oxide . The salt deposits may have been left behind when leaked salt water evaporated. Since the salts found are usually colorless, other elements such as iron or sulfur are likely to be responsible for the reddish color.

Speculations about life on Europe

Possible connections between Europe's underground ocean and the surface

The possible presence of liquid water has led to speculation as to whether forms of life can exist in Europe's oceans . Life forms have been discovered on earth that can survive under extreme conditions without the presence of sunlight, for example in hydrothermal springs ( black smokers ) or in the deep sea .

According to a report in the science magazine New Scientist , NASA scientists planning the canceled NASA mission Jupiter Icy Moons Orbiter , after evaluating previous missions in spring 2004, concluded that the moon Europe could be far more hostile to life than previously assumed.

Hydrogen peroxide and areas covered by concentrated sulfuric acid were detected on the surface . It is assumed here that the acid comes from the ocean assumed under the ice sheet. The concentration is explained by submarine volcanism , which can be responsible for the sulfur .

Europe is also in a very close position to Jupiter or, more precisely, to its radiation belt. This means that Europe is exposed to particularly high levels of exposure. There are also organisms on earth that do not seem to mind high radiation values, but for higher living beings or even humans they would make colonization extremely difficult or even impossible.

It is quite possible that the sulfur came from Jupiter's moon Io . There are now also indications that the presumed ocean below the surface of Europe has a significant salt concentration. Thus epsomite detected on the surface (a magnesium sulfate compound). Epsomit could have been created by reaction of the sulfur from Jupiter's moon Io with magnesium chloride under the influence of radiation. The magnesium chloride comes with high probability from the interior of Europe. Epsomit is much easier to detect in the infrared range than sodium or potassium chloride , which one would rather assume to be in Europe.

Spectroscopic investigations showed that larger amounts of sodium chloride can be found on the surface of Europe. It is not known whether it came from inside the moon.

To avoid contamination of Europe with terrestrial microorganisms , the Galileo space probe, which was the last to observe Europe, was allowed to burn up in Jupiter's atmosphere .

So far there is no evidence of life, but later missions should clarify this. It is thinking of an unmanned cryobot space probe that will land on the surface, melt through the ice crust and release a kind of “mini submarine” into Europe's ocean. Before this mission can even become a reality, a Europa Orbiter space probe could be launched in the 2020s to enter orbit around Europe and extensively study the moon. It is hoped that this will provide further knowledge about Europe and find suitable landing sites for later missions.

Exploration through probe missions

After the probes Pioneer 10 and Pioneer 11 flew past in 1973 and 1974, there were at least blurry photographs of Jupiter's largest moons. Voyager 1 and Voyager 2 provided much more accurate images and data when they passed by in 1979. In 1995, the Galileo probe began orbiting Jupiter for eight years. She also carried out detailed investigations and measurements on the Galilean moons , on which most of our current knowledge about these celestial bodies is based.

Scheduled missions

Artistic concept illustration: a cryobot (top left in the background) exposes a hydro robot.

The ESA space agency plans to launch the JUICE probe in 2022, which will investigate the Jupiter moons Ganymede , Callisto and Europe, with the focus on investigating the suspected oceans below the surface. Several Flybys are to take place in Europe as part of the mission around 2030. The NASA plans to Mission Europe Clipper with a start date in the 2020s. Over 40 flights past Europe are planned, through which detailed images of the lunar surface will be collected. This mission is also to investigate the moons Ganymede and Callisto by Flybys in addition to Europe. In the distant future, a melting probe to drill its way through the ice mantle could be sent to the moon Europa. Several scientific institutions such as the German Aerospace Center (DLR) are currently working on corresponding prototypes.

Europe in popular culture

The speculations generally made by scholars about life in Europe are taken up from time to time in works of pop culture. In the science fiction film 2010: The year in which we make contact from 1984 (screenplay: Arthur C. Clarke ) you can hear an off - screen voice representing an unspecified, highly developed extraterrestrial intelligence, the following Sentence say:

“All these worlds are yours - except Europe. Attempt no landing there. Use them together. Use them in peace. "

“All of these worlds are yours - except Europe. Don't try to land there. Use them together. Use them in peace. "

The science fiction film Europa Report from 2013 is about a manned space mission to Jupiter's moon Europa, during which the crew of the lander encounters large, complex and apparently dangerous creatures. They inhabit the ocean below the ice crust of Europe, which in the film is in places hardly thicker than the ice cover on a frozen lake in winter.

In the video game Barotrauma by the German game developer and publisher Daedalic , you explore the ocean of the moon with submarines.

literature

  • A Science Strategy for the Exploration of Europe. The National Academies, Space Studies Board, 1999 (English, nap.edu ).
  • Robert T. Pappalardo, William B. McKinnon, Krishan Khurana (Eds.): Europe. The University of Arizona Press, Tucson AZ 2009, ISBN 978-0-8165-2844-8 .

Web links

Commons : Europe  - collection of images, videos and audio files

Individual evidence

  1. a b NASA Jovian Satellites Fact Sheet , vestibules, orbital speed, surface and brightness calculated from it.
  2. ^ Europakrater in the Gazetteer of Planetary Nomenclature of the IAU (WGPSN) / USGS ; last accessed on December 31, 2017.
  3. SA Kattenhorn, LM Prockter: Subduction on Europe: The Case for Plate Tectonics in the Ice Shell. 45th Lunar and Planetary Science Conference, March 17-21, 2014, The Woodlands, Texas. Abstract # 1003 (PDF; 231 kB)
  4. ^ Clay-Like Minerals Found on Icy Crust of Europa . nasa.gov, December 11, 2013; accessed: January 9, 2014
  5. JPL: Hubble Sees Evidence of Water Vapor at Jupiter Moon , December 12, 2013, accessed January 15, 2014
  6. ^ A b J. D. Anderson, G. Schubert, RA Jacobson, EL Lau, WB Moore, WL Sjogren: Europa's Differentiated Internal Structure: Inferences from Four Galileo Encounters. In: Science . Volume 281, 1998, pp. 2019-2022, doi: 10.1126 / science.281.5385.2019
  7. ^ Nicole A. Spaun, James W. Head III: A model of Europa's crustal structure: Recent Galileo results and implications for an ocean. Journal of Geophysical Research: Planets. Volume 106, No. E4, 2001, pp. 7567-7576, doi: 10.1029 / 2000JE001270
  8. ^ Francis Nimmo, Michael Manga: Geodynamics of Europa's Icy Shell. In: Pappalardo et al. (Ed.): Europe. 2009 (see literature ), pp. 381–404
  9. Sascha Haupt: New knowledge about water on Jupiter's moon Europe. Article on Raumfahrer.net from November 16, 2011 contributions from BBC News and Nature
  10. Martin Vieweg: Icy candidate for extraterrestrial habitats. Retrieved September 6, 2019 . Article on Wissenschaft.de from November 17, 2011, based on Rolf Müller et al .: Nature, ( doi: 10.1038 / nature10608 )
  11. Kattenhorn, Simon; Prockter, Louise (2014): Evidence for subduction in the ice shell of Europa . Nature Geosciences 7 (9). doi: 10.1038 / ngeo2245
  12. ^ PH Figueredo, R. Greeley: Resurfacing history of Europa from pole-to-pole geological mapping . In: Icarus , 167 (2), 2004, p. 287, bibcode : 2004Icar..167..287F , doi: 10.1016 / j.icarus.2003.09.016
  13. ^ Preston Dyches, Dwayne Brown, Michael Buckley: Scientists Find Evidence of `` Diving '' Tectonic Plates on Europa . NASA September 8, 2014; Retrieved September 8, 2014.
  14. ^ Life could be tough on acid Europe. In: New Scientist . February 15, 2004, accessed October 10, 2014 .
  15. Stefan Deiters: Jupiter's moon Europe, ocean could be like earthly seas . Astronews.com, 6/8 March 2013; accessed March 12, 2013
  16. Stefan Deiters: Jupiter's moon Europe, the underground ocean even more terrestrial? . Astronews.com, June 19, 2019; accessed July 15, 2019
  17. ESA: JUICE - Science Objectives. Retrieved February 8, 2020 .
  18. ^ NASA: Europa Clipper - About the Mission. Retrieved February 8, 2020 .
  19. Europa Clipper: Development phase for Europa probe begins. In: www.astronews.com. Retrieved December 3, 2016 .
  20. Mission Europa Clipper - Search for life on Jupiter's ice moon . In: Deutschlandfunk . ( deutschlandfunk.de [accessed on December 3, 2016]).
  21. ^ Barotrauma. In: Barotrauma. Retrieved April 17, 2020 (American English).
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This version was added to the list of articles worth reading on January 16, 2006 .