Scientists think that many of Jupiter's moons started out as drifting chunks of rock that became ensnared by the planet's gravitational pull. Before wrapping things up, we should talk about lunar behavior. Many of the Jovian moons orbit in the same direction in which Jupiter spins. But there are those which go the opposite way — including nine of the new moons discovered by Sheppard and his colleagues.
With so many bodies revolving in different directions, collisions are inevitable. Moons that crash into one another might well be destroyed in the process. Just as Jupiter acquires new moons, it's finding ways to lose some of the older ones. According to the astronomer Neil F. Comins, if planet Earth had two moons instead of one, our nights would get brighter because there'd be twice as much sunlight reflecting off of lunar surfaces.
Also, we'd see significantly higher tides, rendering many coastal areas uninhabitable. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots.
Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. The Solar System. Four of the many moons orbiting Jupiter are shown. Why does this planet have so many moons? Various groupings of Jovian moons with the newly discovered ones shown in bold. The 'oddball,' called Valetudo after the Roman god Jupiter's great-granddaughter, has a prograde orbit that crosses the retrograde [opposite direction] orbits.
Now That's Interesting. Cite This! Try Our Sudoku Puzzles! Both missions provided more information on these satellites during a few brief hours of encounter than had been assembled in the years since their discovery. They are shown here in their correct positions relative to Jupiter, but are not to scale. The largest moon in the solar system, Ganymede, is larger than the planet Mercury. Amalthea, one of the small Jovian moons, is highly irregular in shape, and keeps its long axis pointed towards Jupiter as it rotates around the planet.
The red color may result from a coating of sulfur ejected by the active volcanism of Io, and "swept up" by Amalthea.
The Moons of Jupiter Jupiter has numerous moons, which make the Jovian system much like a miniature solar system. Williams The Galilean Satellites The four Galilean satellites of Jupiter were faint dots of light in astronomers' telescopes before the encounters of the Pioneer and Voyager spacecraft. The constant change in size and orientation of Io causes friction that creates enough internal heat for volcanic eruptions to occur. Ganymede, Europa and Io are all in orbital resonance with Jupiter.
Io completes exactly four orbits and Europa completes exactly two orbits in the same time it takes Ganymede to complete one orbit around Jupiter. During the course of their orbits, the three moons line up like in the picture seen to the left. Since they periodically line up in this fashion, the gravitational tugs the moons exert on each other stretch their orbits into elliptical shapes.
Europa's surface and crust are made almost entirely of water ice, and its bizarre, fractured appearance is proof enough that tidal heating has acted there. The icy surface is nearly devoid of impact craters and may be only a few million years old. Observations made by the Galileo spacecraft show that Europa has a metallic core and a rocky mantle. Surrounding the rocky interior appears to be an icy layer kilometers thick, the top few kilometers of which seem to be frozen solid.
The stretching and squeezing of tidal friction should provide enough heat to melt some of this into liquid water beneath a thin ice shell.
If it does, then Europa may have an ocean with more than twice as much liquid water as all of Earth's oceans combined. Close-up photos of the surface of Europa support the idea of a liquid ocean beneath the surface.
These photos, taken by the Galileo spacecraft, show what appears to be icebergs stuck in a layer of ice. Other evidence comes from double-ridged cracks on the surface.
Tidal flexing that allows water to well up and build ridges may create these cracks. The surface of Ganymede shares many similarities with Europa. Ganymede's surface is also made of water ice, but unlike Europa's surface, it shows signs of varying age. The darker regions are heavily cratered, suggesting they are billions of years old. The lighter regions show no signs of craters and it is thought that eruptions of water covered the surface before freezing over.
These areas are geologically younger than the darker regions.
0コメント