You would expect impacts at the distance of Jupiter to be lower than near Earth, but I guess they can be higher if the impactor got a velocity boost by Jupiter slingshot effect.
The 40 billion years problem is 40 million years ago according to this report. That somewhat aligns with Saturn ring system ages said to be perhaps million years old according to some sources. It is believed that such an impact occurred around 40 million years ago. Ganymede orbits Jupiter, not Saturn.
I think the article meant 4 billion years old. I am not so sure that impacts necessarily explains Ganymede's internal differentiaton as opposed to Callisto's homogeny. Ganymede certainly formed closer to Jupiter than Callisto, where there would be a greater abundance of heavier elements. Ganymede certainly has more iron internaly than Callisto. There appears to have been enough iron to form an inner iron rich core and an outer iron sulphide outer core like the Earth and Mercury Ganymede is unique among the solar system moons to have a dual layered core.
This separation would have generated enough heat for the layers to form within Ganymede. Europa and Io are also very heavily differentiated, though they both appear to have singular layered cores, so this makes sense. Does not mean though Ganymede did not have enormous impacts though.
The sciencedaily. Asteroids are rocky and usually heavily cratered due to a long history of impacts with other asteroids and possibly comets. Old impact craters on asteroids have beem deformed and erased by newer impact craters. Alternatively, impact events can disintegrate asteroids into smaller pieces. This asteroid, Mathilde, is interesting because of the large size of the impact craters on its surface. Despite the obvious intensity of the impacts, the asteroid was not destroyed. Scientists believe the asteroid must be uncommonly dense to have withstood such bombardment.
This image mosaic of asteroid Mathilde is constructed from four images acquired by the NEAR spacecraft on June 27, The outer gas planets do not have solid surfaces, but their moons do. Most of these moons are rocky, icy worlds with a variety of surface features and compositions. How did Mercury get its name?
Who discovered Mercury? How many spacecraft have been to Mercury? How old is Mercury? What is Mercury made of? What does the Sun look like from Mercury? Discovered in by NASA's Voyager 1 spacecraft, Jupiter's rings were a surprise, as they are composed of small, dark particles and are difficult to see except when backlit by the Sun.
Data from the Galileo spacecraft indicate that Jupiter's ring system may be formed by dust kicked up as interplanetary meteoroids smash into the giant planet's small innermost moons.
Jupiter took shape when the rest of the solar system formed about 4. Jupiter took most of the mass left over after the formation of the Sun, ending up with more than twice the combined material of the other bodies in the solar system. In fact, Jupiter has the same ingredients as a star, but it did not grow massive enough to ignite. About 4 billion years ago, Jupiter settled into its current position in the outer solar system, where it is the fifth planet from the Sun. The composition of Jupiter is similar to that of the Sun — mostly hydrogen and helium.
Deep in the atmosphere, pressure and temperature increase, compressing the hydrogen gas into a liquid. This gives Jupiter the largest ocean in the solar system — an ocean made of hydrogen instead of water. Scientists think that, at depths perhaps halfway to the planet's center, the pressure becomes so great that electrons are squeezed off the hydrogen atoms, making the liquid electrically conducting like metal.
Jupiter's fast rotation is thought to drive electrical currents in this region, generating the planet's powerful magnetic field. It is still unclear if deeper down, Jupiter has a central core of solid material or if it may be a thick, super-hot and dense soup. It could be up to 90, degrees Fahrenheit 50, degrees Celsius down there, made mostly of iron and silicate minerals similar to quartz.
The planet is mostly swirling gases and liquids. The extreme pressures and temperatures deep inside the planet crush, melt, and vaporize spacecraft trying to fly into the planet. Jupiter's appearance is a tapestry of colorful cloud bands and spots. The gas planet likely has three distinct cloud layers in its "skies" that, taken together, span about 44 miles 71 kilometers. The top cloud is probably made of ammonia ice, while the middle layer is likely made of ammonium hydrosulfide crystals. The innermost layer may be made of water ice and vapor.
The vivid colors you see in thick bands across Jupiter may be plumes of sulfur and phosphorus-containing gases rising from the planet's warmer interior. Jupiter's fast rotation — spinning once every 10 hours — creates strong jet streams, separating its clouds into dark belts and bright zones across long stretches.
With no solid surface to slow them down, Jupiter's spots can persist for many years. Stormy Jupiter is swept by over a dozen prevailing winds, some reaching up to miles per hour kilometers per hour at the equator.
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