Europe (satellite)
Europa is the sixth natural satellite of Jupiter in increasing distance and the smallest of the four Galilean satellites. It was discovered in 1610 by Galileo and named by Europa, the mother of King Minos of Crete and lover of Zeus. Simon Marius suggested the name upon its discovery, but this name, as well as the name of the other Galilean satellites, did not come into common use until the mid-20th century. In much of the early astronomical literature it is referred to by its Roman numeral designation, Jupiter II, or as Jupiter's second satellite. In addition to having been observed by ground-based telescopes, several space probes (the first in the early 1970s) have examined it up close. It is the sixth largest satellite in the solar system.
Slightly smaller than the Moon, Europa is composed mainly of silicates, has a crust of water ice and a likely iron-nickel core. It has a tenuous atmosphere composed of oxygen, among other gases. Its surface is streaked with cracks and streaks, while craters are relatively rare. It has the smoothest surface of any known object in the solar system. This apparent youth and smoothness has given rise to the hypothesis that an ocean exists below the surface, which could serve as an abode for life. This hypothesis proposes that heat from tidal forces causes the ocean to remain liquid. and drive geologic activity just as plate tectonics would. On September 8, 2014, NASA reported that it had found evidence supporting early indications of plate tectonics in Europa's thick ice cap, the first sign of such geologic activity. on a world other than Earth. On 12 May 2015, several scientists announced that sea salt from the subsurface ocean may be coating some geological features on Europa, suggesting that the ocean is interacting with the sea floor. This may be important in determining whether the satellite could be suitable for life.
History
Europa was discovered by Galileo on January 7, 1610, the date he found next to Jupiter "three fixed stars, totally invisible due to their small size", as he noted in his diary. The following night he discovered a fourth star, and on subsequent nights he found that they orbited the planet, from which he deduced that they were satellites. They were Io, Europa, Ganymede and Callisto. Galileo initially called these moons "Medicean stars", in honor of his patron, Cosimo II de' Medici, but other astronomers did not like the proposal, who sought alternatives; Thus, the German Simon Marius, who claimed to have also discovered the moons even before Galileo, proposed names based on Greek mythology, which are known today. Galileo countered by proposing that they be called Jupiter I, II, III, and IV, names that were used until the early XX, when the names proposed by Marius were recovered. Jupiter's four moons are also known as the "Galilean satellites".
Orbit and rotation
Europa orbits Jupiter in just over three and a half days, with an orbital radius of about 670,900 kilometers. Its eccentricity (ε) is only 0.009, so its orbit is almost circular, and the orbital inclination with respect to Jupiter's equatorial plane is small, 0.470°. Like its fellow Galileans, Europa is tidally locked to Jupiter, with one hemisphere constantly facing Jupiter.
The slight eccentricity of Europa's orbit, maintained by gravitational perturbations from the other Galilean satellites, causes Europa to contract and stretch throughout its orbit. As Europa gets a little closer to Jupiter, Jupiter's gravitational pull increases, causing Europa to stretch out toward it. As Europa moves slightly away from Jupiter, the gravitational pull decreases, causing Europa to revert back to a more spherical shape, creating the tides in its ocean. Europa's orbital eccentricity is continually driven by its orbital resonance with Io. Thus, tidal flexing kneads Europa's interior and gives it a source of heat, possibly allowing its ocean to remain liquid. The ultimate source of this energy is Jupiter's rotation, which is drained by Io through Jupiter-raising tides and transferred to Europa and Ganymede by orbital resonance.
Physical characteristics
Internal structure
Europa's composition is similar to that of the inner planets, being composed mainly of siliceous rocks. It has an outer layer of water about 100 km thick (part as crustal ice, part as liquid ocean under the ice). Recent data on the magnetic field observed by the Galileo probe indicate that Europa creates a magnetic field due to interaction with Jupiter's magnetic field, suggesting the presence of a layer of fluid, probably a saltwater liquid ocean. It may also have a small metallic iron core.
This weak magnetic field (about 1/4 the strength of Ganymede's magnetic field and similar to Callisto's) varies periodically as it passes through Jupiter's strong magnetic field. On March 2, 1998 NASA announced, based on data sent by Galileo, the discovery of evidence that there is conductive material under the surface of Europa, most likely a salty ocean. Spectrographic evidence suggests that dark reddish areas and other features on Europa's surface appear to be rich in salts such as magnesium sulfate, probably deposited by water evaporating from the interior. Salts are usually colorless or white, so there must be another substance present that contributes to the reddish color; it is believed to be sulfur (perhaps from Io), or iron compounds.
In December 2013, the Hubble telescope detected water vapor fumaroles being shot from the surface, which confirmed certain related theories about the possible existence of water under the surface crust of the satellite. These observations were contrasted as a result of the review of the data collected by the Galileo probe in its closest approach, below 400 km, on December 16, 1997. In these measurements, sudden changes in the magnetic field values were observed, with decreases of up to 200 nT, and the plasma density, with a rapid increase up to 2000 cm-3. Using various models, it was deduced that these measurements could correspond to navigation through the fumarole of a geyser of liquid water under the surface.
Surface
The surface of Europa is very smooth. Few landforms greater than a few hundred meters in height have been observed. The significant crisscross markings on Europa's surface appear to be caused by differences in albedo, with little vertical relief. There are few craters on Europa, only three craters larger than 5 km in diameter: Pwyll, at 39 km in diameter, is the best known. Europa's albedo is one of the largest of all the moons. This could indicate a young and active surface; based on estimates of the frequency of comet bombardment Europa likely endures, its surface cannot be more than 30 million years old. The low relief and visible markings on Europa's surface resemble those of an icy ocean on Earth, and it is thought that beneath Europa's icy surface is a liquid ocean that is kept warm by heat generated by gravitational tides. from Jupiter. Europa's surface temperature is 110 K (-163 °C) at the equator and only 50 K (-223 °C) at the poles. The largest craters appear to be filled with new, flat ice; Based on this and the amount of heat generated on Europa by tidal forces, it is estimated that the solid ice crust is about 10-30 km thick, which may mean that the liquid ocean is 90 km deep. km.
The most striking feature of Europa's surface is a series of dark streaks that crisscross the entire surface of the moon. These veins resemble cracks in sea ice on Earth; close examination shows that the edges of Europa's crust on either side of the rifts are displaced from their original position. The largest bands are about 20 km across with fuzzy outer edges, regular striations, and a central band of lighter material, thought to have been caused by a series of volcanic eruptions of water or geysers as the crust opened up. and the warmer layers of the interior being exposed. The effect is similar to that observed on Earth in the mid-oceanic ridge or rift zone. These fractures are believed to have been caused in part by tidal forces exerted by Jupiter. Europa's surface is thought to shift up to 30 meters between high and low tide. Since Europa is tidally locked (at neap tide, like the Moon to Earth) with Jupiter and always maintains the same orientation toward the planet, the forces must follow a distinctive and predictable pattern. Only the most recent fractures in Europe appear to fit this predictable pattern; other fractures appear to have occurred in increasingly different orientations the older they are. This could be explained if Europa's surface had rotated slightly faster than its interior, an effect that is possible, given that the ocean decouples the moon's surface from its rocky mantle and the pulling effect of Jupiter's gravity on the outer crust. of the moon. Comparisons of Voyager and Galileo photos suggest that Europa's crust rotates at most once every 10 millennia relative to its interior.
Another feature present on the surface of Europa are "freckles" or lenticular, circular or elliptical surfaces. Many are vaults, others holes, and still others smooth dark spots; others have an uneven texture. The surfaces of the domes look like bits of the surrounding older plains that have been pushed up.
One hypothesis suggests that they formed from blocks of warmer ice that rose relative to cooler ice in the crust, similar to what occurs with magma chambers in the Earth's crust. The smooth dark spots they may have formed from liquid water that has escaped from the interior when the ice surface fractured. And the irregular freckles (called 'chaos' regions, for example Conamara) seem to have formed from many small fragments of crust on top of smooth dark patches, like icebergs in a frozen sea.
Another alternative hypothesis suggests that these lenticular surfaces are actually zones of chaos, and the so-called pits, blobs, and hills are the result of an early interpretation of the low resolution of Galileo's images. Which would imply that the ice is too thin to support the convective diapir model.
Atmosphere
Recent Hubble Space Telescope observations indicate that Europa has a very tenuous atmosphere (10−12 bar pressure at the surface) composed of oxygen. Of the moons in the solar system, only seven of them (Io, Callisto, Ganymede, Titan, Triton, Enceladus and Titania) are known to have atmospheres. Unlike the oxygen in Earth's atmosphere, that in Europa's atmosphere is almost certainly of non-biological origin. It is most likely generated by sunlight and charged particles colliding with Europa's icy surface., producing water vapor that is later split into hydrogen and oxygen. Hydrogen manages to escape Europa's gravity, but oxygen does not.
Life in Europe
It has been proposed that life may exist in this hypothetical ocean under the ice, perhaps supported in an environment similar to that existing in the depths of Earth's oceans near volcanic vents or in Lake Vostok on the Antarctica. There is no evidence to support this hypothesis; however, efforts have been made to avoid any possibility of contamination. The Galileo mission ended in September 2003 with the spacecraft's collision with Jupiter. If the ship had simply been abandoned, unsterilized, it could have collided with Europa in the future, contaminating it with terrestrial microorganisms. The introduction of these microorganisms would have made it nearly impossible to determine whether Europa had ever undergone its own biological evolution, independent of Earth.
In a recent study it has been estimated that Europe has a sufficient amount of liquid water and that it has a high concentration of oxygen, even higher than in our seas. Similar concentrations would be enough to support not only microorganisms, but more complex life forms.
According to Schulze-Makuch, there could be microorganisms that would be very similar to those on earth, grouped in some fumaroles that, according to the hypothesis, could exist at the bottom of the seas. However, since these fumaroles are few, the colonies of these microorganisms could not be many or very large, so in the event of complex life forms, they could not be greater than one gram in mass.
Due to its proximity to Jupiter, Europa suffers from powerful radiation of 5400 mSv/day, exposure enough to kill a person in one day.
Europe in fiction and cinema
- Europe plays an important role in Arthur C's film and book. Clarke 2010: Odyssey dos and its continuation. Very advanced forms of extraterrestrial life are interested in the primitive forms of life under the ice of Europe and through the monoliths transform Jupiter into a star (called Lucifer) to accelerate the evolution of the "Europeans". In 2061: Odyssey threeEurope has become a tropical ocean.
- In Greg Bear's novel The frige of God (1987), Europe is destroyed by aliens. Two large pieces of ice in Europe are thrown into collision with Mars.
- In the movie Europe Report (2013), the satellite is visited by the Europa One space mission in search of life.
- Europe is the stage of the video game prologue "Call of Duty: Infinite Warfare" in its campaign mode. Also in the multiplayer mode is a playable map described as a research center located above the icy surface of Europe.
- The 2D video game "Barotrauma" takes place in the ocean of Europe, where the player has encounters with different monsters.
- In the video game Destiny 2, Europe is the main location of the Expansion: Beyond the Light.
Exploration
The space exploration of Europe began with the flybys of the probes Pioneer 10 and 11 in 1973 and 1974 respectively. The photographs taken by these probes were of low quality compared to those of later missions. The two Voyagers crossed the Jupiter system in 1979 and provided more detailed images of its icy surface. Seeing them, many scientists conjectured the possible existence of a subsurface ocean. From 1995 to 2003, the Galileo probe orbited Jupiter. It is the most detailed reconnaissance of the Galilean satellites to date and included the Galileo Europa Mission and the Galileo Millennium Mission, with numerous close flybys of Europa. New Horizons imaged Europa as it passed through the Jovian system on its way to Pluto.
Future Missions
Conjectures of extraterrestrial life have endowed Europe with great interest and have led to constant political pressure to schedule new missions. The objectives of these missions range from examining the chemical composition of the satellite to searching for extraterrestrial life in the hypothetical internal ocean. Robotic missions will have to withstand the high radiation surrounding Europa and Jupiter. Europa receives about 5.4 Sv of radiation per day.
- The JUICE (Jupiter Icy Moons Explorer) of the European Space Agency (ESA), plans observation missions to Europe, whose launch is estimated for 2022.
- NASA has since 2013 its European Clipper program, planned for 2025, which consists of astrobiology missions to find life in Europe.
Gallery
| Images of chaotic land in Europe | |||||||||
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| Color Images of Europe | |||||||||
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| Different geographical accidents | |||||||||
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