One of jupiters moons is as big as the planet mercury, if the moon is so big why is it a moon and not a planet
826306
Because although the moon is as big as a planet, it does not have the characteristics of a planet. Jupiter's moon is a moon because it displays characteristics of a moon, like orbiting Jupiter and being stuck into Juptier's gravational pull.
390184
Jupiter is the largest planet in the solar system. Its diameter is 88,846 miles (142,984 kilometers), more than 11 times that of Earth, and about one-tenth that of the sun. It would take more than 1,000 Earths to fill up the volume of the giant planet. When viewed from Earth, Jupiter appears brighter than most stars. It is usually the second brightest planet -- after Venus.\n\nJupiter is the fifth planet from the sun. Its mean (average) distance from the sun is about 483,780,000 miles (778,570,000 kilometers), more than five times Earth's distance. Ancient astronomers named Jupiter after the king of the Roman gods.\n\nAstronomers have studied Jupiter with telescopes based on Earth and aboard artificial satellites in orbit around Earth. In addition, the United States has sent six space probes (crewless exploratory craft) to Jupiter.\n\nAstronomers witnessed a spectacular event in July 1994, when 21 fragments of a comet named Shoemaker-Levy 9 crashed into Jupiter's atmosphere. The impacts caused tremendous explosions, some scattering debris over areas larger than the diameter of Earth.\n\nPhysical features of Jupiter\n\nJupiter is a giant ball of gas and liquid with little, if any, solid surface. Instead, the planet's surface is composed of dense red, brown, yellow, and white clouds. The clouds are arranged in light-colored areas called zones and darker regions called belts that circle the planet parallel to the equator.\n\nOrbit and rotation\n\nJupiter travels around the sun in a slightly elliptical (oval-shaped) orbit. The planet completes one orbit in 4,333 Earth days, or almost 12 Earth years.\n\nAs Jupiter orbits the sun, the planet rotates on its axis, an imaginary line through its center. The axis is tilted about 3¡. Scientists measure tilt relative to a line at a right angle to the orbital plane, an imaginary surface touching all points of the orbit.\n\nJupiter rotates faster than any other planet. It takes 9 hours 56 minutes to spin around once on its axis, compared with 24 hours for Earth. Scientists cannot measure the rotation of the interior of the giant planet directly, so they have calculated the speed from indirect measurements. They first calculated the speed using an average of the speeds of the visible clouds that move with interior currents, except for a more rapid zone near the equator.\n\nJupiter sends out radio waves strong enough to be picked up by radio telescopes on Earth. Scientists now measure these waves to calculate Jupiter's rotational speed. The strength of the waves varies under the influence of Jupiter's magnetic field in a pattern that repeats every 9 hours 56 minutes. Because the magnetic field originates in Jupiter's core, this variation shows how fast the plant's interior spins.\n\nJupiter's rapid rotation makes it bulge at the equator and flatten at the poles. The planet's diameter is about 7 percent larger at the equator than at the poles.\n\nMass and density\n\nJupiter is heavier than any other planet. Its mass (quantity of matter) is 318 times larger than that of Earth. Although Jupiter has a large mass, it has a relatively low density. Its density averages 1.33 grams per cubic centimeter, slightly more than the density of water. The density of Jupiter is about 1/4 that of Earth. Because of Jupiter's low density, astronomers believe that the planet consists primarily of hydrogen and helium, the lightest elements. Earth, on the other hand, is made up chiefly of metals and rock. Jupiter's mix of chemical elements resembles that of the sun, rather than that of Earth.\n\nJupiter may have a core made up of heavy elements. The core may be of about the same chemical composition as Earth, but 20 or 30 times more massive.\n\nThe force of gravity at the surface of Jupiter is up to 2.4 times stronger than on Earth. Thus, an object that weighs 100 pounds on Earth would weigh as much as 240 pounds on Jupiter.\n\nThe atmosphere of Jupiter is composed of abou
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in relation to the other planets in our solar system... our moon is bigger than pluto but smaller than the other planets.\n\nin relation to other moons of other planets in our solar system... it is the 5th largest out of all the other planetary satellites.\n\nthe exact figures are at the link below:\n-(this other link might help as well)
141708
Yes. It's actually in our own solar system.  Whether it is a planet or not is the real question.  It is really small.  While bigger than pluto, it is still smaller than the Earth's moon!
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We have 8 'planets' (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune).  We have several more 'dwarf planets.'  \n\nThe difference is that, during planet formation, a planet's gravity will pull in all the material around it, leaving a planet surrounded \nby empty space.  This is referred to as 'clearing the neighborhood.'  A dwarf planet's gravity is not sufficient to pull in all the material around it, so it does not clear its neighborhood.  \n\nPluto is now a dwarf planet, along with several asteroids and other celestial bodies.  In fact, Pluto is a binary planet, because it and it's moon, Charon, orbit each other (the center of Charon's orbit is not a point inside of Pluto, but rather a point between the two bodies).  So Pluto probably won't even be considered a dwarf planet for long.\n\nThis Xena, as you call it, is twice the size of Pluto.  That's what reignited this whole controversy.  It's real name is 2003UB313.  Xena was only given to it as a temporary name.
370080
Finally a good question.\n\nThe Moon's apparent size being very similar to the Sun's apparent size is a coincidence. But the Moon doesn't always cover the Sun during an eclipse, look up annular eclipse (the looks smaller), and when it does cover it, it is usually a bit larger.\n\nBut now let's talk about the main question.\n\nWe always see the same side of the Moon because its during its full rotation around the Earth it also makes a full rotation around its axis. This is not a coincidence. There are several satellites in the solar system whose rotation is synchronized with their rotation around a planet (eg. Io around Jupiter, Charon around Pluto but also Pluto around Charon :-) etc. ).\n\nThe Earth's gravitation decreases with the distance from its center. So the Moon's opposite side (which is further away from the Earth) is attracted less by the Earth than the side which is closer. This results in the Moon being a little bit deformed along the Earth-Moon line.\nThe Moon is a little bit shaped like an egg: if it would rotate faster, it would not be elongated towards the Earth anymore, and the Earth's gravitation would try to turn it back. This is very difficult to explain without the opportunity to draw figures ... but anyway, search for tidal locking on the net, I hope you'll find a good, illustrated explanation.\n\n\nEDIT: In one answer someone said that Mercury is in a similar relation with the Sun ... this is not exactly true, as the ratio of period of its rotation and the period of its orbiting is 3/2.\n\nMercury also has an elongated shape: due to this 3:2 resonance, at its perihelion, the axis of its elongation is always parallel with the Sun--Mercury axis.\n\nEDIT2: As I said, the apparent size of the Moon is just a concidence. Other planents do get total eclipses. What does a total eclipse mean? It means that a moon casts a shadow on the planet: http://www.c-science.com/txt/images/1999/990428unssx2.jpg\n\nThere is a nice program calles Celestia, which can show you the eclipses caused by various moons on various planets (3D animations): http://www.shatters.net/celestia/
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The earth would have more craters than the moon almost, had it not developed an atmosphere.  The atmosphere burns up anything trying to pass through it into a tiny meteorite.\n\nSame reason that mercury is battered with the asteroids.
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Jupiter is the fifth planet from the Sun and is the largest one in the solar system. If Jupiter were hollow, more than one thousand Earths could fit inside. It also contains more matter than all of the other planets combined. It has a mass of 1.9 x 1027 kg and is 142,800 kilometers (88,736 miles) across the equator. Jupiter possesses 28 known satellites, four of which - Callisto, Europa, Ganymede and Io - were observed by Galileo as long ago as 1610. Another 12 satellites have been recently discovered and given provisional designators until they are officially confirmed and named. There is a ring system, but it is very faint and is totally invisible from the Earth. (The rings were discovered in 1979 by Voyager 1.) The atmosphere is very deep, perhaps comprising the whole planet, and is somewhat like the Sun. It is composed mainly of hydrogen and helium, with small amounts of methane, ammonia, water vapor and other compounds. At great depths within Jupiter, the pressure is so great that the hydrogen atoms are broken up and the electrons are freed so that the resulting atoms consist of bare protons. This produces a state in which the hydrogen becomes metallic. \nColorful latitudinal bands, atmospheric clouds and storms illustrate Jupiter's dynamic weather systems. The cloud patterns change within hours or days. The Great Red Spot is a complex storm moving in a counter-clockwise direction. At the outer edge, material appears to rotate in four to six days; near the center, motions are small and nearly random in direction. An array of other smaller storms and eddies can be found through out the banded clouds. \n\nAuroral emissions, similar to Earth's northern lights, were observed in the polar regions of Jupiter. The auroral emissions appear to be related to material from Io that spirals along magnetic field lines to fall into Jupiter's atmosphere. Cloud-top lightning bolts, similar to superbolts in Earth's high atmosphere, were also observed.
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Mercury actually does have an atmosphere but the planet's small size makes it hard to retain.  It is not stable.
75743
Twertyto's answer is the best! When I was just learning about astronomy I asked the same question. Someone told me a very simple answer that just might work for you:  A planet reflects light and a star creates it. That sounds simple enough for simpler times! But now welcome to the 21st century!!!\nBrown dwarfs are kind of the "animal" that bridges these two seemingly different objects. Astronomy is having a hard (but fun) time right now trying to decide exactly what a planet is- from the very large to the very small. Is an object 75 times the size of Jupiter a planet? 79 times? 81 times? No one seems to know. Do we call them planets or officially name them Brown Dwarfs. On the other side of the issue, is Pluto a planet? They just discovered a larger than Pluto object and several almost-the-size-of-Pluto objects out past Pluto's orbit. Are all of these planets? If Pluto's not a planet, but now has been discovered to have at least 3 moons (two new one's were just discovered recently), then what do we call it? \nThis has been a surprisingly tough answer for Astronomers as well, so not only is it a great question, but you- and everyone else- might have to stick around for a while for the difinitive answer!!!
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Titan really isn't all that big.  It's not even the largest moon in the solar system!  Titan only has a radius of about 2575 miles, which is only .4 times the size of earth.  Jupiter and Saturn are much much much bigger so we can actually make out details in small telescopes, but considering the fact that Titan is just about 930 million miles away, its not surprising we can't make out much about Titan.\n\nAlso a problem with directly observing Titan is that it has such a thick atmosphere that we can't see the surface.  So we have to send things like Huygens to get underneath the clouds.
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I'll assume you meant "in the solar system"\n\n -  "pluto" isn't a planet! It's just a big block of dirty ice...\n\n -  The biggest planet is Jupiter, and is made of gas.\n\n -  The smallest would be mercury, which is right next to the sun.\n\n -  It would be hard to say which planet is "medem", since there are really big planets (the gas giants: Jupiter, Saturn, Uranus, and Neptune), and really small ones: (the inner planets: Mercury, Venus, the Earth and Moon, and Mars)
180202
Neither. It's the mass of the planet itself. Everything that has mass projects a gravitational field. The more massive an object is, the bigger its gravitational "pull". This is why objects like the Sun can support several large planets, while Pluto (which has a moon about a third the size of it) gets pulled around by its moon.
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A common confusion; Triton is the largest moon of Neptune, with a diameter of 2,700 kilometers (1,680 miles). It was discovered by William Lassell, a British astronomer, on October 10, 1846 scarcely a month after Neptune was discovered. \n\nTitan is the largest moon of Saturn. Discovered by Christiaan Huygens in 1655, Titan is larger than the Earth and the second largest moon in the solar system, rivalled only by Jupiter's moon Ganymede. \n\nI have seen photos of the surface of Titan and its sand and rocks are an orangey red colour. A probe (Huygens) landed there.
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32.675 AU for jupiter's circumference, and 2.406 AU for mercury.  Jupiter is the largest planet in our solar system.
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The inner planets are called the terrestrial planets and are defined by being small rocky bodies with small atmospheres if any at all.  The outer planets are called the jovian planets and are defined by being large in size with giant gas atmospheres.  Due to their mass they tend to have many moons and a ring system (all four do).  \n\nWhat mainly gives rise to this difference is twofold. \n1. Temperature\n2. Chemical differentiation\n\nSince the gas giants are so cold they are able to retain more of an atmosphere since the slower moving gases in them are less able to escape gravity.\nAlso, as the solar system formed heavy element "sank" to the inner portions of the solar disk while lighter elements were left behind to the outer regions to collect into the giant planets.\n\nInside the gas giants is a rocky type core but this is encased in the giant atmospheric envelope that surrounds them.\n\nThis is the short of it.
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Jupiter has 63 moons or "natural satellites" ... http://www.answers.com/jupiter's%20moons\n\nThey have ALL been named ...\n\nThe Voyager 1 mission discovered three inner moons in 1979, bringing the total then known to 16 (17 if one counted Themisto, which had been found but then lost in 1975). The total rested there until 1999. Since then, researchers using sensitive ground-based detectors have recovered Themisto and found a further 46 tiny moons in long, eccentric, generally retrograde orbits. They average 3 kilometres in diameter, and the largest is barely 9 km across. All of these moons are thought to be captured asteroidal or perhaps cometary bodies, possibly fragmented into several pieces, but very little is actually known about them. The total number of known moons of Jupiter now stands at 63, currently the most of any planet in the solar system. Many additional tiny moons may exist that have not yet been discovered.