However, Europa's surface is not at all like anything in the inner solar system. Its surface is exceedingly smooth with few features more than a few hundred meters high.
There are very few craters on Europa; only three craters larger than 5 km in diameter have been found. From the observations of water ice absorption bands, and due to the near absence of impact craters, we have inferred that the surface is ice rich and also very young and active, perhaps only 30 million years old.
The precise age of Europa's surface is unknown. Voyager mapped only a fraction of the surface at high resolution. The amount of tidal deformation depends on whether there is an ocean just below the surface or if Europa is solid throughout. Thus, precise measurements of the shape of Europa may provide details about the structure of the subsurface ocean. The Europa Orbiter would also collect additional high resolution images and gravity observations of Europa. Jupiter is surrounded by very strong radiation belts that are dangerous to spacecraft.
The Galileo spacecraft dipped deep into the radiation belts for only a few days every few months. In contrast, the Europa Orbiter would be exposed to strong radiation for a much longer period of time.
Because of the high cost of designing a spacecraft to endure such radiation perhaps one billion dollars , the proposed mission is currently on hold. Titan 7.
With a radius of kilometers, it is the second largest moon in the entire Solar System and is larger than the planets Mercury and Pluto. Titan is the only satellite in the Solar System to have a significant atmosphere.
At the surface, the atmospheric pressure is 1. The atmosphere is composed primarily of nitrogen, as on Earth, and also includes some methane and possibly argon. Trace amounts of hydrogen and many organic molecules are also present. Some of these compounds form a thick haze layer in the upper atmosphere of Titan. At visible wavelengths, this haze makes it impossible to see down to the surface of Titan. Ultraviolet radiation from the Sun can break up methane molecules, and the resulting hydrogen atoms can be lost to space.
The remnants of the methane can form heavier organic compounds, such as ethane and acetylene. Over the age of the Solar System, an ocean of ethane several hundred meters thick might have formed, probably with some methane dissolved in it. The actual distribution of ethane, whether in a surface ocean or in subsurface cavities, is not known at present. Infrared images of Titan obtained by the Hubble Space Telescope show a pattern of bright and dark regions that some scientists think might be related to oceans and continents.
Radar observations of Titan also hint at the possibility of oceans and continents. The Cassini spacecraft was launched in October and will arrive at Saturn in July In the event that the probe lands in an ethane ocean, it is able to float.
Ice Rafts This Galileo image is 42 kilometers across and is illuminated from the right. Chaos Region This Galileo image is kilometers across and is illuminated from the left.
If it can be demonstrated that life formed independently in two places around the same star, it would then be reasonable to suspect that life springs up in the universe fairly easily once the necessary ingredients are present, and that life might be found throughout our galaxy and the universe.
If life were found at Europa, how might it change your view of the cosmos and our place in it? So if we replaced our Moon with Europa, it would appear roughly the same size in the sky as our Moon does, but brighter — much, much brighter.
Europa orbits Jupiter at about , miles , kilometers from the planet, which itself orbits the Sun at a distance of roughly million miles million kilometers , or 5. One AU is the distance from Earth to the Sun. Light from the Sun takes about 45 minutes to reach Europa. Because of the distance, sunlight is about 25 times fainter at Jupiter and Europa than at Earth.
Europa orbits Jupiter every 3. Jupiter takes about 4, Earth days or about 12 Earth years to orbit the Sun a Jovian year. Over time, the orbits of most large satellites or planets tend to become circular, but in the case of these three satellites, the resonance produces a forced eccentricity since the satellites line up with each other at the same points in their orbits over and over, giving each other a small gravitational tug that keeps their orbits from becoming circular.
If Europa's ocean exists, the tidal heating could also lead to volcanic or hydrothermal activity on the seafloor, supplying nutrients that could make the ocean suitable for living things.
Those four moons are likely about the same age as the rest of the solar system — about 4. Each planet in the inner solar system is less dense than their inner neighbor — Mars is less dense than Earth, which is less dense than Venus, which is less dense than Mercury. The Galilean moons follow the same principle, being less dense the farther they are from Jupiter.
The reduced density at greater distances is likely due to temperature: denser, rocky, and metal material condenses out first, close to Jupiter or the Sun, while lighter-weight icy material only condenses out at larger distances where it is colder.
Distance from Jupiter also determines how much tidal heating the Galilean satellites experience — Io, closest to Jupiter, is heated so much that it is the most volcanically active body in the solar system, and it likely long ago drove off any water it had when it formed. The features seen on Europa's surface document both internal and external processes shaping the icy crust.
Internal processes and the possible presence of liquid water beneath the ice are indicated by features such as "dark spots", lobe-shaped flow features, "puddles", "mottled terrain", knobs, pits, and the darker areas along ridges and triple bands.
Europa is subjected to constant tugging from the giant planet, Jupiter, as well as from its neighboring moons, Io and Ganymede. This causes "tidal" forces that affect Europa's interior and surface. Evidence for such forces includes ridges, fractures, wedge-shaped bands, and areas of "chaos. Impact craters document external effects on a planet's surface.
Although present on Europa, impact craters are relatively scarce compared to the number seen on Ganymede, Callisto, and on the surfaces of most other "rocky" planets and moons in our solar system. This scarcity of craters suggests that the surface of Europa is very young. These images have resolutions from 89 feet 27 meters to 4. This color image of the Jovian moon Europa was acquired by Voyager 2 during its close encounter on Monday morning, July 9,
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